waters form integral components of downstream food webs, providing
nursery habitat for breeding fish and amphibians, colonization
opportunities for stream invertebrates, and maturation habitat for
stream insects. Covered adjacent waters serve an important role in the
integrity of traditional navigable waters, interstate waters, and the
territorial seas by subsequently releasing (desynchronizing)
floodwaters and retaining large volumes of stormwater, sediment,
nutrients, and contaminants that could otherwise negatively impact the
condition or function of traditional navigable waters, interstate
waters, and the territorial seas.
    Floodplain areas connect aquatic environments through both surface
and shallow subsurface hydrologic flowpaths. Waters in these areas are
therefore uniquely situated in watersheds to receive and process water
that passes over densely vegetated areas and through subsurface zones
before reaching streams and rivers. When contaminants reach a
floodplain water, they can be sequestered in sediments, assimilated
into wetland plants and animals, transformed into less harmful and/or
mobile forms or compounds, or lost to the atmosphere. Wetlands located
in floodplains store large amounts of sediment and organic matter from
upstream and upland areas. In addition, the primary function of many
floodplain wetlands in the Western United States is sediment exchange,
which can transform materials and compounds temporarily on floodplains.
    Wetlands and other similar waters in floodplain areas act as
buffers that are among the most effective tools for mitigating nonpoint
source pollution. The literature shows that collectively, wetlands and
other similar waters improve water quality through assimilation,
transformation, or sequestration of nutrients, sediment, and other
pollutants--such as pesticides and metals--that can affect downstream
water quality. These pollutants enter floodplain wetlands from dry and
wet atmospheric deposition, runoff from upland agricultural and urban
areas, spray drift, subsurface water flows, outfalls, pipes, and
ditches.
    Floodplain waters, including wetlands, can reduce flood peaks by
storing and desynchronizing floodwaters. They can also maintain river
baseflows by recharging alluvial aquifers. Many studies have documented
the ability of floodplain wetlands to reduce flood pulses by storing
excess water from streams and rivers. One review of wetland studies
reported that floodplain wetlands reduced or delayed floods in 23 of 28
studies. For example, peak discharges between upstream and downstream
gaging stations on the Cache River in Arkansas were reduced 10-20
percent primarily due to floodplain water storage.
    Ecosystem function within a river system is driven by interactions
between the physical environment and the diverse biological communities
living within the river system. Wetlands in floodplains become
important seed sources for the river network, especially if
catastrophic flooding scours vegetation and seed banks in other parts
of the channel. Movements of organisms that connect aquatic habitats
and their populations, even across different watersheds, are important
for the survival of individuals, populations, and species, and for the
functioning of the river ecosystem. For example, lateral expansion and
contraction of the river in its floodplain results in an exchange of
matter and organisms, including fish populations that are adapted to
use floodplain habitat for feeding and spawning during high water. The
organisms that live within the hyporheic zone for these mid- and large-
sized river systems have a demonstrated connection outward to several
miles within the floodplain. General field practice observations
further indicate that covered adjacent waters with a close proximity
have a significant nexus with the downstream waters.
    Waters adjacent to impoundments and covered tributaries are
integrally linked to the chemical, physical, and biological functions
of the waters to which they are adjacent and, through those waters, are
integrally linked to the chemical, physical, and biological functions
of the downstream traditional navigable waters, interstate waters, or
the territorial seas. Thus, where waters are adjacent to impoundments
or covered tributaries, they also have a significant nexus to the
downstream traditional navigable waters, interstate waters, or the
territorial seas. The important functions that covered adjacent waters
perform that impact downstream traditional navigable waters, interstate
waters, and the territorial seas and their integrated behavior with the
tributary system demonstrate why all waters adjacent to traditional
navigable waters, interstate waters, or the territorial seas as well as
impoundments and covered tributaries, alone or in combination with
other

covered adjacent wetlands in a watershed have a significant nexus with
those downstream waters.
    Based on the science and their technical expertise and experience,
the agencies determine it is appropriate to protect all covered
adjacent waters because those waters are functioning as an integrated
system with the downstream traditional navigable waters, interstate
waters, or the territorial seas and significantly affect such
downstream waters. Consequently, these waters are ``adjacent'' and
therefore ``waters of the United States'' under the CWA. Covered
adjacent waters are ``waters of the United States'' without the need
for further analysis.
3. Case-Specific Significant Nexus Determinations
a. Two Exclusive Circumstances for Case-Specific Significant Nexus
Determinations
    The rule identifies two exclusive circumstances under which a
significant nexus determination is made on a case-specific basis to
determine whether the water is a ``water of the United States.'' First,
there are five subcategories of waters--Prairie potholes, Carolina and
Delmarva bays, pocosins, western vernal pools in California, and Texas
coastal prairie wetlands--that the agencies conclude must be analyzed
``in combination'' as ``similarly situated '' waters when making a
case-specific significant nexus analysis. Second, there are waters for
which the agencies have made no conclusions with respect to which
waters are ``similarly situated'' but for which a case-specific
significant nexus analyses may be undertaken. The rule establishes that
case-specific determinations may be made for waters located within the
100-year floodplain of a traditional navigable water, interstate water,
or the territorial seas, and for waters located within 4,000 feet from
the high tide line or the ordinary high water mark of traditional
navigable waters, interstate waters, the territorial seas,
impoundments, or tributaries.
b. Summary of Rationale for ``Similarly Situated'' Determinations
    Based on the agencies' expertise and experience and available
literature and data, the agencies have determined that waters in the
five subcategories of waters identified in paragraph (a)(7) are
similarly situated and must be combined with other waters in the same
subcategory located in the same watershed that drains to the nearest
traditional navigable water, interstate water, or the territorial seas.
See Technical Support Document. The scientific literature shows that
these subcategories of waters are frequently located together in a
complex or are otherwise closely co-located and perform similar
functions. The agencies specifically sought comment in the proposal on
options to address these five subcategories of waters, including
whether waters in these subcategories should be found ``similarly
situated'' by rule.
    Based on the body of scientific literature regarding the
subcategories of waters specified in paragraph (a)(7) and their
functions, the agencies determined that waters of the specified
subcategories are similarly situated because they perform similar
functions and they are located sufficiently close to each other to
function together in affecting downstream waters and therefore
reasonably be evaluated in combination with regard to their effects on
the integrity of traditional navigable waters, interstate waters, or
the territorial seas. The specified subcategories of waters perform
similar functions as waters of the same subcategory in the same single
point of entry watershed and collectively function together to affect a
traditional navigable water, interstate water, or the territorial seas.
Among the functions and relationships in the landscape the agencies
considered to conclude that the subcategories are each similarly
situated are the physical capacity of the waters to provide flood and
sediment retention. In determining that the waters in each of the five
subcategories are ``similarly situated,'' the agencies concluded that
these subcategories of waters are co-located to each other or similar
to the tributary system such that they have cumulative and additive
effects on pollutant removal through parallel, serial, or sequential
processing, such as the role of pocosins in maintaining water quality
in estuaries. The subcategories of waters are sufficiently near each
other or the tributary system to function as an integrated habitat that
can support the life-cycle of a species or more broadly provide habitat
to a large number of a single species.
    The SAB expressed support for the agencies' option in the preamble
of the proposed rule to identify certain subcategories of waters as
similarly situated and highlighted these same five subcategories. It
stated, ``[t]here is also adequate scientific evidence to support a
determination that certain subcategories and types of `other waters' in
particular regions of the United States (e.g., Carolina and Delmarva
Bays, Texas coastal prairie wetlands, prairie potholes, pocosins,
western vernal pools) are similarly situated (i.e., they have a similar
influence on the physical, chemical and biological integrity of
downstream waters and are similarly situated on the landscape) and thus
could be considered waters of the United States. Furthermore, as the
science continues to develop, other sets of wetlands may be identified
as `similarly situated.' '' SAB 2014b at 3.
    The agencies concluded that the specific subcategories of waters
listed in paragraph (a)(7) are similarly situated for purposes of a
case-specific significant nexus based on the following:
    (i) Prairie potholes are a complex of glacially formed wetlands,
usually occurring in depressions that lack permanent natural outlets
that are found in the central United States and Canada. In the United
States, they are found from central Iowa through western Minnesota,
Montana, eastern South Dakota, and North Dakota. Prairie potholes
demonstrate a wide range of hydrologic permanence; some hold permanent
standing water and others are wet only in years with high
precipitation. This in turn influences the diversity and structure of
their biological communities.
    Prairie potholes generally accumulate and retain water effectively
due to the low permeability of their underlying soil, which can
modulate flow characteristics of nearby streams and rivers. One of the
most noted hydrologic functions of Prairie potholes is water storage.
Because most of the water outflow in Prairie potholes is via
evapotranspiration, Prairie potholes can become water sinks, preventing
flow to downstream waters. Prairie potholes also can accumulate
chemicals in overland flow, thereby reducing chemical loading to other
bodies of water. When Prairie potholes are artificially connected to
streams and lakes through drainage, they become sources of water and
chemicals to downstream waters. Prairie potholes also support a
community of highly mobile organisms, from plants to invertebrates that
move among Prairie potholes and that can biologically connect the
entire complex to the river network.
    Prairie potholes can be highly connected to other Prairie potholes
via shallow subsurface connections and via surface hydrologic
connections during the wet season. They can also be connected to the
stream network via surface and shallow subsurface connections. Intense
precipitation events or high cumulative precipitation over one or more
seasons can result in temporary hydrologic connectivity between Prairie
potholes and from

Prairie potholes to the tributary system via ``fill-and-spill'' events.
    Their density across the landscape varies from region to region as
the result of several factors, including patterns of glacial movement,
topography, and climate. In some parts of the region, prairie pothole
density is very high. Though their density varies across the landscape,
Prairie potholes often act as a complex. They have similar functions
that can collectively impact downstream waters.
    Prairie potholes have been determined to be similarly situated
based on the characteristics of Prairie potholes, including their
density on the landscape, their interaction and formation as a complex
of wetlands and open waters, their connections to each other and the
tributary network, and their similar functions. In addition, their
chemical, physical, and biological connections to downstream waters and
the strength of their effects on the chemical, physical, or biological
integrity of a traditional navigable water, interstate water, or the
territorial seas support this determination that Prairie potholes are
similarly situated by rule.
    (ii) Carolina and Delmarva bays are ponded depressional wetlands
that occur along the Atlantic coastal plain from northern Florida to
New Jersey. Though Carolina and Delmarva bays are from the same
category of wetland and perform similar functions, they are located in
different parts of the Atlantic coastal plain and thus have unique
names. Carolina bays are most abundant in North Carolina and South
Carolina, while Carolina bays found in the Delmarva Peninsula are
commonly referred to as Delmarva bays or Delmarva potholes.
    Most bays receive water through precipitation, lose water through
evapotranspiration, and lack natural surface outlets. Both mineral-
based and peat-based bays have shown connections to shallow
groundwater. Bays typically are in proximity to each other or to
streams, providing for hydrologic connections to each other and to
downstream waters in large rain events via overland flow or shallow
subsurface connections. Some Delmarva bays have surface water
connections to the Chesapeake Bay. In addition, human channeling and
ditching of the bays are widespread and create surface connections to
other waters, including the tributary system and estuaries. These
ditches commonly connect the surface water of bays to other bays that
are lower on the landscape, and ultimately, to streams.
    The hydrology in bays allow for denitrification (chemical and
biological processes that remove nitrogen from water), which can reduce
the amount of nitrate in both groundwater and downstream surface
waters. Because bays are frequently connected chemically to downstream
waters through ditches, they can be sources of sediment and nutrients
to downstream waters. Where they are not connected via confined surface
connections, bays can act as sediment and nutrient sinks.
    Fish are reported in bays that are known to dry out, indirectly
demonstrating surficial connections. Amphibians and reptiles use bays
extensively for breeding and for rearing young. These animals can
disperse many feet on the landscape and can colonize, or serve as a
food source to, downstream waters. Similarly, bays foster abundant
insects that have the potential to become part of the downstream food
chain. Humans have ditched and channelized a high percentage of bays,
creating new surface connections to downstream waters and allowing
transfer of nutrients, sediment, and other pollutants, such as
methylmercury.
    Carolina and Delmarva bays can occur in high density on the
landscape and can act as a wetlands complex. Bays have similar
functions to other bays and cumulatively these functions can impact
downstream waters.
    The agencies conclude that Carolina and Delmarva bays are similarly
situated based on their close proximity to each other and the tributary
network, their hydrologic connections to each other and the tributary
network, their density on the landscape, and their similar functions.
    (iii) The word pocosin comes from the Algonquin Native American
word for ``swamp on a hill,'' and these evergreen shrub and tree-
dominated wetlands are found from Virginia to northern Florida, but
mainly in North Carolina. Typically, there is no standing water present
in these peat-accumulating wetlands, but a shallow water table leaves
the soil saturated for much of the year. They range in size from less
than an acre to several thousand acres. The slow movement of water
through the dense organic matter in pocosins removes excess nutrients
deposited by rainwater. The same organic matter also acidifies the
water. This water is slowly released to downstream waters and
estuaries, where it helps to maintain the proper salinity, nutrients,
and acidity.
    Because pocosins are the topographic high areas on the regional
landscape, they serve as the source of water for downstream waters.
Pocosins often have seasonal connections to drainageways leading to
estuaries or are adjoining other wetlands draining into perennial
streams or estuaries. Other pocosins have been ditched and are directly
connected to streams.
    The agencies conclude that pocosins are similarly situated based on
their close proximity to each other and the tributary network, their
hydrologic connections to each other and the tributary network, their
density on the landscape, and their similar functions.
    (iv) Western vernal pools are shallow, seasonal wetlands that
accumulate water during colder, wetter months and gradually dry up
during warmer, drier months. Western vernal pools are seasonal wetlands
from the Pacific Northwest to northern Baja California, Mexico
associated with topographic depressions, soils with poor drainage,
mild, wet winters and hot, dry summers. The agencies have determined
that California vernal pools are ``similarly situated.''
    Because their hydrology and ecology are so tightly coupled with the
local and regional geological processes that formed them, western
vernal pools in California typically occur within ``vernal pool
landscapes,'' or complexes of pools in which swales connect pools to
each other and to seasonal streams. Some common findings about the
hydrologic connectivity of western vernal pools include evidence for
temporary or permanent outlets, frequent filling and spilling of higher
pools into lower elevation swales and stream channels, and conditions
supporting subsurface flows through pools without perched aquifers to
nearby streams.
    Non-glaciated vernal pools in western states are reservoirs of
biodiversity and can be connected genetically to other locations and
aquatic habitats through wind- and animal-mediated dispersal. Animals
and other organisms can move between western vernal pool complexes and
streams. Insects and zooplankton can be flushed from vernal pools into
streams and other waters during periods of overflow, carried by animal
vectors (including humans), or dispersed by wind.
    The agencies conclude that western vernal pools in California are
similarly situated based on their close proximity to each other and the
tributary network, their interaction and arrangement as a complex of
wetlands, their hydrologic connections to each other and the tributary
network, their density on the landscape, and their similar functions.
    (v) Along the Gulf of Mexico from western Louisiana to south Texas,
freshwater wetlands occur as a mosaic

of depressions, ridges, intermound flats, and mima mounds. These
coastal prairie wetlands were formed thousands of years ago by ancient
rivers and bayous and once occupied almost a third of the landscape
around Galveston Bay, Texas. The term Texas coastal prairie wetlands is
not used uniformly in the scientific literature but encompasses Texas
prairie pothole (freshwater depressional wetlands) and marsh wetlands
that are described in some studies that occur on the Lissie and
Beaumont Geological Formations, and the Ingleside Sand.
    Texas coastal prairie wetlands are locally abundant and in close
proximity to other coastal prairie wetlands and function together
cumulatively. Collectively as a complex, Texas coastal prairie wetlands
can be geographically and hydrologically connected to each other via
swales and connected to downstream waters, contributing flow to those
downstream waters. Cumulatively, these wetlands can control nutrient
release levels and rates to downstream waters, as they capture, store,
transform, and pulse releases of nutrients to those waters.
    The agencies conclude that Texas coastal prairie wetlands are
similarly situated based on their close proximity to each other and the
tributary network, their hydrologic connections to each other and the
tributary network, their interaction and formation as a complex of
wetlands, their density on the landscape, and their similar functions.

IV. Definition of ``Waters of the United States''

A. Summary of the Rule

    The rule revises the existing definition of ``waters of the United
States'' consistent with the CWA, science, the agencies' technical
expertise and experience, and Supreme Court decisions. The final rule
establishes categories of waters that are jurisdictional and other
categories of waters that are excluded, as well as categories of waters
and wetlands that require a case-specific significant nexus evaluation
to determine if they are ``waters of the United States'' and covered by
the CWA. The rule also provides definitions for key terms used in the
regulation. The final rule retains much of the structure of the
agencies' longstanding definition of ``waters of the United States,''
and many of the existing provisions of that definition where revisions
are not required in light of Supreme Court decisions or other bases for
revision. All existing exclusions from the definition of ``waters of
the United States'' are retained, and several exclusions reflecting
longstanding agencies' practice are added to the regulation for the
first time.
    The agencies define ``waters of the United States'' in paragraph
(a) of the rule for all sections of the CWA to include the traditional
navigable waters (a)(1), interstate waters (a)(2), the territorial seas
(a)(3), impoundments of jurisdictional waters (a)(4), covered
tributaries (a)(5), and covered adjacent waters (a)(6). Waters in these
categories are jurisdictional ``waters of the United States'' by rule--
no additional analysis is required. This eliminates the need to make a
case-specific significant nexus determination for covered tributaries
or covered adjacent waters because the agencies determined that these
waters have a significant nexus to waters identified in (a)(1) through
(a)(3) of the rule and thus are ``waters of the United States.'' The
agencies emphasize that the finding of jurisdiction for these covered
tributaries and covered adjacent waters was not based on the mere
connection of a water body to downstream waters, but rather a
determination that the nexus, alone or in combination with other of
these covered tributaries or covered adjacent waters in the watershed,
is significant.
    The agencies exclude specified waters from the definition of
``waters of the United States'' in paragraph (b) of the rule. The rule
makes no substantive change to the existing exclusion for waste
treatment systems designed consistent with the requirements of the CWA
and makes no change to the existing exclusion for prior converted
cropland. The rule excludes for the first time certain waters and
features over which the agencies have generally not asserted CWA
jurisdiction, as well as groundwater, which the agencies have never
interpreted to be a ``water of the United States'' under the CWA.
Codifying these longstanding practices supports the agencies' goals of
providing greater clarity, certainty, and predictability for the
regulated public and regulators, and makes rule implementation clear
and practical.
    This final rule provides clear exclusions for certain types of
ditches. The final rule also expressly excludes stormwater control
features created in dry land and certain wastewater recycling
structures created in dry land. Waters and features that are excluded
under paragraph (b) of the rule cannot be determined to be
jurisdictional under any of the categories in the rule under paragraph
(a).
    In addition to waters that are categorically ``waters of the United
States'' or categorically excluded under paragraphs (a) and (b), the
rule identifies certain waters that can be ``waters of the United
States'' only where a case-specific determination has found a
significant nexus between the water and traditional navigable waters,
interstate waters, or the territorial seas. First, paragraph (a)(7) of
the rule specifies five types of waters (Prairie potholes, Delmarva and
Carolina bays, pocosins, western vernal pools in California, and Texas
coastal prairie wetlands) that the agencies have determined to be
``similarly situated,'' and thus are to be considered in combination in
a significant nexus analysis. Second, paragraph (a)(8) specifies that
waters located within the 100-year floodplain of a traditional
navigable water, interstate water, or the territorial seas, and waters
located within 4,000 feet from the high tide line or the ordinary high
water mark of traditional navigable waters, interstate waters, the
territorial seas, impoundments, or covered tributaries may be found to
have a significant nexus on a case-specific basis, but the agencies
have not made a determination that the waters are ``similarly
situated.'' As a result, a significant nexus analysis for these waters
will include a case-specific assessment of whether there are any
similarly situated waters, as well as whether the water, alone or in
combination with any waters determined to be similarly situated, has a
significant nexus to a traditional navigable water, interstate water,
or territorial sea. The rule outlines at (c)(5)(i)-(ix) functions
relevant to these case-specific significant nexus analyses.
    Paragraph (c) of the rule provides definitions for key terms used
in the regulation. Some of these are unchanged from the current
regulations, including the definitions for ``wetlands'' at (c)(4),
``ordinary high water mark'' at (c)(6) and ``high tide line'' at
(c)(7), although the latter two are existing, unchanged Corps'
definitions added to EPA's regulations for the first time. 33 CFR
328.3(d)-(e). The rule also defines for the first time ``tributary''
and ``tributaries'' at (c)(3), ``neighboring'' (an aspect of adjacency)
at (c)(2), and ``significant nexus'' at (c)(5).
    This rule is effective on August 28, 2015. Under existing Corps'
regulations and guidance, approved jurisdictional determinations
generally are valid for five years. The agencies will not reopen
existing approved jurisdictional determinations unless requested to do
so by the applicant or, consistent with existing Corps' guidance,
unless new information warrants revision of the determination before
the expiration period. Similarly, consistent with existing regulations
and guidance, approved jurisdictional determinations

associated with issued permits and authorizations are valid until the
expiration date of the permit or authorization.
    As a general matter, the agencies' actions are governed by the rule
in effect at the time the agency issues a jurisdictional determination
or permit authorization, not by the date of a permit application,
request for authorization, or request for a jurisdictional
determination. However, any jurisdictional determinations issued prior
to the effective date of the rule and jurisdictional determinations
associated with permit applications deemed by the Corps to have been
complete on the date this rule is published in the Federal Register,
including complete pre-construction notifications, will be made
consistent with the existing rule, unless the applicant requests that
its approved jurisdictional determination or permit authorization be
decided after the effective date of the new rule. Reliance on
preliminary jurisdictional determinations is also not affected by the
issuance of this rule. All other jurisdictional determinations and
requests for authorization requiring an approved jurisdictional
determination issued on or after the effective date of this rule will
be made consistent with this rule.
    It is important to emphasize that the agencies do not anticipate
being able to complete new jurisdictional determinations submitted
after this rule is published before it becomes effective. As a result,
requesters seeking jurisdictional determinations after the rule is
published should expect the determination will be made consistent with
this rule. The agencies recognize there are a number of requests for
permit applications and requests for jurisdictional determinations
pending at any time. The agencies expect only a small portion of those
pending actions will require additional information from or work by the
requester. As described in the Economic Analysis, the vast majority of
requests address streams and adjacent wetlands, and the agencies do not
expect new information or work will be needed to complete those
requests. If any additional information is needed to assess these
requests, the agencies will work proactively with permit applicants to
reduce potential short-term disruptions in the permit process that may
be associated with the rule.

B. Traditional Navigable Waters

    The existing regulations include within the definition of ``waters
of the United States'' all waters that are currently used, or were used
in the past, or may be susceptible to use in interstate or foreign
commerce, including all waters which are subject to the ebb and flow of
the tide. See, e.g., 33 CFR 328.3(a)(1); 40 CFR 230.3(s)(1); 40 CFR
122.2 (``waters of the U.S.''). This paragraph of the regulation
encompasses those waters that are often referred to as ``traditional
navigable waters.'' The rule does not make any changes to this
paragraph of the regulation.
    For purposes of CWA jurisdiction, waters will be considered
traditional navigable waters, and jurisdictional under (a)(1) of the
rule, if they:
     Are subject to section 9 or 10 of the Rivers and Harbors
Appropriations Act of 1899;
     Have been determined by a Federal court to be navigable-
in-fact under Federal law;
     Are waters currently being used for commercial navigation,
including commercial waterborne recreation (for example, boat rentals,
guided fishing trips, or water ski tournaments);
     Have historically been used for commercial navigation,
including commercial waterborne recreation; or
     Are susceptible to being used in the future for commercial
navigation, including commercial waterborne recreation.
    See Technical Support Document; ``U.S. Army Corps of Engineers
Jurisdictional Determination Form Instructional Guidebook Appendix D,
`Traditional Navigable Waters,''' available at: http://www.usace.army.mil/Portals/2/docs/civilworks/regulatory/cwa_guide/app_d_traditional_navigable_waters.pdf.
    The agencies received several comments on the scope of traditional
navigable waters. Some commenters observed that ``traditional navigable
waters'' as a jurisdictional category is not based in science. Several
commenters thought that the final rule should specify considerations to
be taken into account when determining if a water is susceptible to
being used in future commercial navigation. The agencies have not
revised the regulation to address susceptibility, but observe that case
law has provided a number of considerations and examples that are
described further in the Technical Support Document and are reflected
in longstanding agencies' practice.

C. Interstate Waters

    The existing regulations define ``waters of the United States'' to
include interstate waters, including interstate wetlands. The rule does
not change that provision of the regulations. Therefore, interstate
waters are ``waters of the United States'' even if they are not
navigable for purposes of Federal regulation under (a)(1) and do not
connect to such waters. Moreover, the rule protects impoundments of
interstate waters, tributaries to interstate waters, waters adjacent to
interstate waters, and waters adjacent to covered tributaries of
interstate waters because they have a significant nexus to interstate
waters. Protection of these waters is thus critical to protecting
interstate waters.
    The language of the CWA indicates that Congress intended the term
``navigable waters'' to include interstate waters without imposing a
requirement that they be traditional navigable waters themselves or be
connected to traditional navigable waters. The precursor statutes to
the CWA subjected interstate waters and their tributaries to Federal
jurisdiction. The text of the CWA, specifically CWA section 303, which
establishes ongoing requirements for interstate waters, in conjunction
with the definition of navigable waters, provides clear indication of
Congress' intent to protect interstate waters that were previously
subject to Federal regulation. Other provisions of the statute provide
additional textual evidence of the scope of the primary jurisdictional
term of the CWA.
    The agencies also have a longstanding regulatory interpretation
that interstate waters fall within the scope of CWA jurisdiction. The
agencies' interpretation was promulgated contemporaneously with the
passage of the CWA and is consistent with the statutory and legislative
history of the CWA. Furthermore, the Supreme Court has never addressed
the CWA's coverage of interstate waters, and it is not reasonable to
read its decisions in SWANCC and Rapanos to question the jurisdictional
status of interstate waters or to impose additional jurisdictional
requirements on interstate waters. The assertion of jurisdiction over
interstate waters is based on the statute and under predecessor
statutes where ``interstate waters'' were defined as all rivers, lakes,
and other waters that flow across, or form a part of, state boundaries.
Pub. L. 80-845, sec. 10, 62 Stat. 1155, at 1161 (1948). The agencies
will continue to implement the provision consistent with the intent of
Congress. For additional discussion of the agencies' interpretation of
the CWA with respect to interstate waters, see Appendix B of the
proposed rule and the Technical Support Document.
    It is reasonable to assert jurisdiction over tributaries, adjacent
waters, and waters that have a significant nexus to interstate waters
consistent with the framework set forth in Justice Kennedy's

opinion in Rapanos for establishing jurisdiction over waters with a
significant nexus to traditional navigable waters. Waters and wetlands
with a significant nexus to traditional navigable waters and interstate
waters have important beneficial effects on those waters, and by
recognizing that polluting or destroying waters with a significant
nexus can harm downstream jurisdictional waters. Traditional navigable
waters and interstate waters cannot be protected without also
protecting the waters that have a significant nexus to those waters as
identified in the rule. The rule thus defines ``waters of the United
States'' to include tributaries to interstate waters, waters adjacent
to interstate waters, waters adjacent to tributaries of interstate
waters, and other waters that have a significant nexus to interstate
waters.
    The agencies received a number of comments on interstate waters.
Some commenters asserted that interstate waters required a significant
nexus to a traditional navigable water in order to be jurisdictional
after Rapanos. The agencies disagree for the reasons described above,
in Appendix B to the proposed rule, and in the Technical Support
Document.

D. Territorial Seas

    The CWA and its existing regulations include ``the territorial
seas'' as a ``water of the United States.'' The rule makes no changes
to that provision of the regulation other than to change the ordering
to earlier in the regulation. The CWA defines ``navigable waters'' to
include ``the territorial seas'' at section 502(7). The CWA goes on to
define the ``territorial seas'' in section 502(8) as ``the belt of the
seas measured from the line of ordinary low water along that portion of
the coast which is in direct contact with the open sea and the line
marking the seaward limit of inland waters, and extending seaward a
distance of three miles.'' The territorial seas establish the seaward
limit of ``waters of the United States.'' The territorial seas are
clearly covered by the CWA (they are also traditional navigable
waters), and it is reasonable to protect their covered tributaries and
covered adjacent waters.
    Although some comments addressed the definition of ``territorial
seas'' provided in the CWA suggesting that the distance thresholds be
revised to reflect other resource statutes, the agencies do not have
authority to revise statutory language.

E. Impoundments

    The existing regulations provide that impoundments of ``waters of
the United States'' remain ``waters of the United States,'' and the
rule does not make any changes to the existing regulatory language.
    Impoundments are jurisdictional because an impoundment of a ``water
of the United States'' remains a ``water of the United States,'' and
because scientific literature demonstrates that impoundments continue
to significantly affect the chemical, physical, or biological integrity
of downstream traditional navigable waters, interstate waters, and the
territorial seas. See Technical Support Document. The Supreme Court has
confirmed that damming or impounding a ``water of the United States''
does not make the water non-jurisdictional. See S. D. Warren Co. v.
Maine Bd. of Envtl. Prot., 547 U.S. 370, 379 n.5 (2006) (``[N]or can we
agree that one can denationalize national waters by exerting private
control over them.''). Similarly, when presented with a tributary to
the Snake River which flows only about two months per year because of
an irrigation diversion structure installed upstream, the Ninth Circuit
noted ``it is doubtful that a mere man-made diversion would have turned
what was part of the waters of the United States into something else
and, thus, eliminated it from national concern.'' U.S. v. Moses, 496
F.3d 984, 988 (9th Cir. 2007), cert. denied, 554 U.S. 918 (2008). As a
matter of policy and law, impoundments do not de-federalize a water,
even where there is no longer flow below the impoundment. The agencies
have analyzed stream networks, above and below impoundments, for
connection to downstream traditional navigable waters, interstate
waters, or the territorial seas. Scientific literature, as well as the
agencies' scientific and technical expertise and experience confirm
that impoundments have chemical, physical, and biological effects on
downstream waters. See Technical Support Document.
    The agencies also note that an impoundment of a water that is not a
``water of the United States'' can become jurisdictional if, for
example, the impounded waters become navigable-in-fact and covered
under paragraph (a)(1) of the rule.
    By their nature, impoundments of jurisdictional waters would also
often meet the definition of ``adjacent waters,'' as they are typically
bordering or contiguous. Impoundments of ``waters of the United
States'' are per se jurisdictional under paragraph (a)(4) of the rule
without the need to determine if they are also adjacent under paragraph
(a)(6). However, as described in section IV.G below, ``adjacent
waters,'' as defined, have a significant nexus to traditional navigable
waters, interstate waters, or the territorial seas, which bolsters the
agencies' determination that impoundments of ``waters of the United
States'' remain ``waters of the United States.''
    Impoundments also may be one of the waters through which
tributaries indirectly contribute flow to a traditional navigable
water, interstate water, or territorial sea. As a matter of law and
science, an impoundment does not cut off a connection between upstream
tributaries and a downstream traditional navigable water, interstate
water, or territorial sea, so covered tributaries above the impoundment
are still considered a tributary to downstream traditional navigable
waters, interstate waters, or the territorial seas even where the flow
of water might be impeded due to the impoundment. See paragraph (a)(5).
    The agencies received comments on impoundments, which generally
explored the impacts of impoundments on connectivity to downstream
waters. For the reasons described above and in the Technical Support
Document, the agencies concluded that impoundments of ``waters of the
United States'' remain ``waters of the United States.''

F. Tributaries

    The existing definition of ``waters of the United States''
regulates all tributaries without qualification. The final rule
protects only waters that have a significant effect on the integrity of
traditional navigable waters, interstate waters, or the territorial
seas. The rule establishes a definition of ``tributary,'' and provides
that a water meeting the definition of tributary, unless it is excluded
under paragraph (b), is a ``water of the United States'' without the
need for a separate case-specific significant nexus evaluation. As
explained in Section III above, covered tributaries and the functions
they provide, alone or in combination with other tributaries in the
watershed, significantly affect the chemical, physical, and biological
integrity of traditional navigable waters, interstate waters, or the
territorial seas. See also Technical Support Document. This section
describes the provisions of the rule addressing tributaries and changes
made to the provisions in the proposed rule based on public comments.

1. What are the provisions in the rule?
    The rule defines ``tributary'' by emphasizing the physical
characteristics created by sufficient volume, frequency and duration of
flow, and that the water contributes flow, either directly or through
another water, to a traditional navigable water, interstate water, or
the territorial seas. This definition is based on the best available
science, intent of the CWA, and case law, and is consistent with
current practice. As mentioned above in Section III, the Science Report
concludes that ``[t]he scientific literature unequivocally demonstrates
that streams, individually or cumulatively, exert a strong influence on
the integrity of downstream waters.'' Science Report at ES-2.
    First, to meet the rule's definition of ``tributary,'' a water must
flow directly or through another water or waters to a traditional
navigable water, interstate water, or the territorial seas. Waters
through which a tributary may contribute flow indirectly include, for
example, impoundments, wetlands, lakes, and other tributaries. A
tributary may contribute flow through any number of downstream waters,
including non-jurisdictional features, such as a ditch excluded under
paragraph (b) of the rule, and jurisdictional waters that are not
tributaries, such as an adjacent wetland--but it must be part of a
tributary system that eventually flows to a traditional navigable
water, an interstate water, or the territorial seas. This limitation on
what constitutes a tributary for purposes of this rule is fundamental.
If a water is not part of the tributary system of a traditional
navigable water, interstate water, or the territorial seas, it does not
meet the definition of ``tributary'' and is not jurisdictional under
this provision of the rule. For example, an intermittent stream that
exists wholly within one state, is not itself a traditional navigable
water, and whose flows eventually ends without connecting to a
traditional navigable water, interstate water, or the territorial seas
is not a ``water of the United States'' as a ``tributary'' for purposes
of this rule. To determine whether a water meets this aspect of the
definition, the connection can be traced using direct observation, U.S.
Geological Survey (USGS) data, stream datasets such as the National
Hydrography Dataset, aerial photography or other reliable remote
sensing information, or other appropriate information.
    Under the rule, flow in the tributary may be perennial,
intermittent, or ephemeral. The agencies received comments suggesting
that the final rule provide definitions for the terms ephemeral flow,
intermittent flow, and perennial flow. The agencies considered the
request and determined that there was no need to include a definition
since they are commonly used scientific terms. Longstanding agencies'
practice considers perennial streams as those with flowing water year-
round during a typical year, with groundwater or contributions of flow
from higher in the stream or river network as primary sources of water
for stream flow. Intermittent streams are those that have both
precipitation and groundwater providing part of the stream's flow, and
flow continuously only during certain times of the year (e.g., during
certain seasons such as the rainy season). Ephemeral streams have
flowing water only in response to precipitation events in a typical
year, and are always above the water table. Precipitation can include
rainfall as well as snowmelt. Science shows that tributaries regardless
of flow duration are very effective at transporting pollutants
downstream, such as excess nutrients and sediment, which impact the
integrity and character of traditional navigable waters, interstate
waters, and the territorial seas. See Technical Support Document.
    Second, the rule requires two physical indicators of flow: There
must be a bed and banks and an indicator of ordinary high water mark.
This definition of ``tributary'' includes only those waters the
agencies have concluded are the type of waters that the CWA was
intended to protect and which either individually or in combination
with other covered tributaries in the watershed have a significant
nexus to a traditional navigable water, interstate water, or the
territorial seas. Thus, the agencies are not defining ``waters of the
United States'' to include all streams that might be considered
``tributaries'' in the general scientific literature. To provide
additional clarity and for ease of use for the public, the agencies are
including the Corps' existing definition of ordinary high water mark in
EPA's regulations as well. Under that existing Corps regulation,
ordinary high water mark indicators include characteristics such as
shelving, scour, changes in soil characteristics, and destruction of
terrestrial vegetation, among others.
    A bed and banks and other indicators of ordinary high water mark
are physical indicators of water flow and are only created by
sufficient and regular intervals of flow. These physical indicators can
be created by perennial, intermittent, and ephemeral flows. See
Technical Support Document. For purposes of the rule, ``bed and banks''
means the substrate and sides of a channel between which flow is
confined. The banks constitute a break in slope between the edge of the
bed and the surrounding terrain, and may vary from steep to gradual.
Existing Corps regulations define ordinary high water mark as the line
on the shore established by the fluctuations of water and indicated by
physical characteristics such as a clear, natural line impressed on the
banks, shelving, changes in the character of soil, destruction of
terrestrial vegetation, the presence of litter and debris, or other
appropriate means that consider the characteristics of the surrounding
areas. 33 CFR 328.3(e). That definition is not changed by the rule and
is added to EPA's regulations.
    Current Corps regulations and guidance identify bed and banks as
indicators of the ordinary high water mark. The definition of
``tributary'' in this rule requires the presence of a bed and banks and
an additional indicator of ordinary high water mark such as staining,
debris deposits, or other indicator identified in the rule or agency
guidance. In many tributaries, the bed is that part of the channel
below the ordinary high water mark, and the banks often extend above
the ordinary high water mark. For other tributaries, such as those that
are incised, changes in vegetation, changes in sediment
characteristics, staining, or other ordinary high water mark indicators
may be found within the banks. In concrete-lined channels, the concrete
acts as the bed and banks and can have other ordinary high water mark
indicators such as staining and debris deposits. Indicators of an
ordinary high water mark may vary from region to region across the
country. See Technical Support Document.
    Other evidence, besides direct field observation, may establish the
presence of bed and banks and another indicator of ordinary high water
mark. The agencies currently use many tools in identifying tributaries
and will continue to rely on their experience and expertise in
identifying the presence of a bed and banks and ordinary high water
mark. For example, several reliable, well-established remote sensing
sources of information or mapping can assist to establish the presence
of water that contributes flow to a traditional navigable water,
interstate water, or the territorial seas and provide evidence
regarding the presence of a bed and banks and another indicator of
ordinary high water mark. Among the types of remote sensing or mapping
information that can assist in establishing the presence of water are
USGS topographic

data, the USGS National Hydrography Dataset (NHD), Natural Resources
Conservation Service (NRCS) Soil Surveys, and State or local stream
maps, as well as the analysis of aerial photographs, and light
detection and ranging (also known as LIDAR) data, and desktop tools
that provide for the hydrologic estimation of a discharge sufficient to
create an ordinary high water mark, such as a regional regression
analysis or hydrologic modeling. These sources of information can
sometimes be used independently to infer the presence of a bed and
banks and another indicator of ordinary high water mark, or where they
correlate, can be used to reasonably conclude the presence of a bed and
banks and ordinary high water mark.
    Both the USGS topographic data and the NHD data assist to delineate
tributaries to traditional navigable waters, interstate waters, or the
territorial seas. Where one or both of these sources have indicated a
``blue line stream,'' there is an indication that the tributary could
exhibit a bed and banks and another indicator of ordinary high water
mark. Where this information is combined with stream order,\11\ more
certainty can result. For example, a water that is a second-order
stream will be more likely to exhibit a bed and banks and another
indicator of ordinary high water mark as compared to a first-order
stream. This information will vary in validity in different parts of
the country, so care will be taken to evaluate additional information
prior to reasonably concluding a bed and banks or other indicators of
ordinary high water mark are associated with the stream. This will be
particularly true for first-order streams and for many streams in the
arid portions of the country. Supporting information that can be used
to conclude the presence of a bed and banks and another indicator of
ordinary high water mark would be the presence of USGS stream data on
the NRCS county Soil Survey or local stream maps which are mapped
independently of the USGS, aerial photography interpretation, or
digital terrain depictions created from LIDAR. See Technical Support
Document.
---------------------------------------------------------------------------

    \11\ Stream order is a method for stream classification based on
relative position within a river network, when streams lacking
upstream tributaries (i.e., headwater streams) are first-order
streams and the junction of two streams of the same order results in
an increase in stream order (i.e., two first-order streams join to
form a second-order stream, and so on). When streams of different
orders join, the order of the larger stream is retained. See Science
Report and Technical Support Document.
---------------------------------------------------------------------------

    Tributaries are observable in aerial photography by their
topographic expression, characteristic linear and curvilinear patterns,
dark photographic tones, and the presence and pattern of riparian
vegetation. The characteristic linear and curvilinear patterns and dark
photographic tones observed on aerial photography can be caused by
shadow cast from the banks of an incised stream or from water in the
stream channel itself. In some cases stream channel morphology is
visible, providing evidence of scour, materials sorting, and
deposition, all characteristics of an ordinary high water mark. Visible
persistent water (e.g., multiple dates of aerial photography showing
visible water) provides strong evidence of the sufficient frequency and
duration of surface flow to create a bed and banks and other indicators
of ordinary high water mark. Visible indicators of running water such
as rapids, riffles, and pools all indicate the presence of a bed and
banks and other indicators of ordinary high water mark. Other physical
characteristics of an ordinary high water mark that may be visible on
aerial photography include the destruction of terrestrial vegetation
and the absence of vegetation in a channel. These indicators gleaned
from aerial photography interpretation can be correlated with the
presence of USGS streams data in reasonably concluding that a bed and
banks and another indicator of ordinary high water mark are present.
See Technical Support Document.
    Additional desktop tools can assist in the identification of bed
and banks and other indicators of ordinary high water mark. For
instance, field staff use other methods for estimating ordinary high
water mark, including, but not limited to, lake and stream gage data,
flood predictions, historic records of water flow, and statistical
evidence. Some desktop tools, such as a regional regression analysis
and the Hydrologic Modeling System (HEC-HMS), provide for the
hydrologic estimation of stream discharge sufficient to create an
ordinary high water mark in tributaries under regional conditions. Such
desktop tools are particularly useful for identifying presence of bed
and banks and another indicator of ordinary high water mark when
supported by additional remote sensing tools that indicate the presence
of such physical features.
    LIDAR is a powerful tool to analyze the characteristics of the land
surface, including tributary identification and characterization. LIDAR
data are becoming more and more widespread for engineering and land use
planning purposes. Where LIDAR data have been processed to create a
bare earth model, detailed depictions of the land surface are
available. Bare earth models reveal subtle elevation changes and can
clearly show a tributary's bed and banks and channel morphology. In
many cases LIDAR can help delineate tributaries that would exhibit a
bed and banks and another indicator of an ordinary high water mark in
greater detail than aerial photography interpretation alone can.
Visible linear and curvilinear incisions on a bare earth model are
strong evidence that a tributary with a bed and banks and another
indicator of an ordinary high water mark is present. LIDAR-indicated
tributaries can be correlated with aerial photography interpretation
and USGS stream data, to reasonably conclude the presence of a bed and
banks and another indicator of an ordinary high water mark in the
absence of a field visit. See Technical Support Document. The agencies
have been using such remote sensing and desktop tools to delineate
tributaries for many years where data from the field are unavailable or
a field visit is not possible.
    In addition, such desktop tools are critical in circumstances where
physical characteristics of bed and banks and another indicator of
ordinary high water mark are absent in the field, often due to
unpermitted alteration of streams. In such cases where physical
characteristics of bed and banks and another indicator of ordinary high
water mark no longer exist, they may be determined by using other
appropriate means that consider the characteristics of the surrounding
areas. Such reliable methods that can indicate prior existence of bed
and banks and other indicators of ordinary high water mark include, but
are not limited to, lake and stream gage data, elevation data, spillway
height, historic water flow records, flood predictions, statistical
evidence, the use of reference conditions, or through the remote
sensing and desktop tools described above.
    The upper limit of the tributary is the point where a bed and banks
and another indicator of ordinary high water mark cease to be
identifiable. The ordinary high water mark establishes the lateral
limits of a water, and its absence generally determines when a
tributary's channel or bed and banks has ended, representing the upper
limit of the tributary. However, a natural or constructed break in bed
and banks or other indicator of ordinary high water mark does not
constitute the upper limit of a tributary where bed and banks or other
indicator ordinary high water mark can be found farther upstream. Note
that waters, including wetlands, which are adjacent to a tributary at
the

upper limit of the channel are jurisdictional as ``adjacent waters.''
    The definition of ``tributary'' includes tributaries that flow
directly or indirectly through impoundments that are jurisdictional
under paragraph (a)(4) of the rule. Tributaries to impoundments of
``waters of the United States'' are jurisdictional for the same reasons
the impoundments themselves are jurisdictional. As discussed in section
IV. E., under case law, an impoundment of a ``water of the United
States'' remains a ``water of the United States,'' and scientific
literature demonstrates that impoundments continue to significantly
affect the chemical, physical, or biological integrity of downstream
waters traditional navigable waters, interstate waters, and the
territorial seas. Therefore, tributaries to such impoundments continue
to have a significant nexus, alone or in combination with other covered
tributaries in the watershed, to the downstream traditional navigable
water, interstate water, or the territorial seas.
    Waters that meet the rule definition of tributary remain
tributaries even if there is a manmade or natural break at some point
along the connection to the traditional navigable water, interstate
water, or the territorial seas. In many tributaries, there are often
natural or constructed breaks in the presence of a bed and banks or
ordinary high water mark while hydrologic connectivity remains. For
example, in some regions of the country where there is a very low
gradient, the banks of a tributary may be very low or may even
disappear at times. Many tributaries lose their ordinary high water
mark when adjacent wetlands are contiguous with the stream channel. The
definition of ``tributary'' addresses these circumstances and states
that waters that meet the definition of tributary remain tributaries
even if such breaks occur, so long as bed and banks and an ordinary
high water mark are present upstream of the break. Under the rule, when
a covered tributary flows through a wetland into another tributary
(sometimes called a ``run-of-stream'' wetland), the covered tributary
remains jurisdictional even though it lost its ordinary high water mark
through the wetland. By looking to the presence of a bed and banks and
an ordinary high water mark upstream, the rule ensures that a mere
break in the ordinary high water mark does not render tributaries with
a significant nexus to downstream waters not jurisdictional. Other
breaks that do not sever jurisdiction include constructed breaks such
as bridges, culverts, pipes, dams, or waste treatment systems, or
natural breaks such as debris piles, boulder fields, or a stream that
flows underground so long as a bed and banks and an ordinary high water
mark can be identified upstream of the break. Site specific conditions
will continue to determine the distance up valley that needs to be
evaluated to see if the break in bed and banks and ordinary high water
mark is temporary or the start of the stream system.
    The rule also clarifies that a water meets the definition of
tributary if the water contributes flow through an excluded feature
such as a ditch with ephemeral flow. While the water above and below
the excluded feature is jurisdictional if it meets the definition of
tributary, the excluded feature does not become jurisdictional. A water
also continues to meet the definition of tributary if at some point the
water contributes flow through a jurisdictional water that is not a
tributary, such as an adjacent wetland or impoundment.
    The agencies' longstanding interpretation of the CWA has included
tributaries that are natural, modified, or constructed waters. While
this rule at paragraph (b) excludes specific types of constructed
waters from jurisdiction, it continues to interpret constructed
tributaries as jurisdictional unless expressly excluded in paragraph
(b). Natural, modified, and constructed tributaries provide many of the
same functions, especially as conduits for the movement of water and
pollutants to other tributaries or directly to traditional navigable
waters, interstate waters, or the territorial seas. The discharge of a
pollutant into a tributary generally has the same effect downstream
whether the tributary waterway is natural, modified, or constructed.
See discussion in section III.C. above and the Technical Support
Document. Given the extensive human modification of watercourses and
hydrologic systems throughout the country, it is often difficult to
distinguish between natural watercourses and watercourses that are
wholly or partly modified or constructed. For example, tributaries that
have been channelized in concrete or otherwise have been modified may
still meet the definition of tributaries under the rule so long as they
have bed and banks and an ordinary high water mark, contribute flow to
a traditional navigable water, interstate water, or the territorial
seas, and are not excluded under paragraph (b). The important
consideration for a modified or constructed water is whether it meets
the definition of ``tributary'' and is not excluded under paragraph
(b).
    Ditches are one important example of constructed features that in
many instances can meet the definition of tributary. Ditches are
jurisdictional under the rule only if they both meet the definition of
``tributary'' and are not excluded under paragraph (b)(3) in the rule.
Not all ditches meet the definition of a tributary, and others--as
discussed in Section I--are expressly excluded from jurisdiction.
    Ditches protected by the rule must meet the definition of
tributary, having a bed and banks and ordinary high water mark, and
contributing flow directly or indirectly through another water to a
traditional navigable water, interstate water, or the territorial seas.
Jurisdictional ditches include ditches such as the following:
     Ditches with perennial flow,
     Ditches with intermittent flow that are a relocated
tributary, or are excavated in a tributary, or drain wetlands,
     Ditches, regardless of flow, that are excavated in or
relocate a tributary.
    The definition of tributary includes natural, undisturbed waters
and those that have been man-altered or constructed, but which science
shows function as a tributary. In addition, alteration or modification
of natural streams and rivers for purposes such as flood control,
erosion control, and other reasons does not convert the tributary to a
ditch. A stream or river that has been channelized or straightened
because its natural sinuosity has been altered, cutting off the
meanders, is not a ditch. A stream that has banks stabilized through
use of concrete or rip-rap (e.g., rocks or stones) is not a ditch. The
Los Angeles River, for example, is a ``water of the United States''
(and, indeed, a traditional navigable water) and remains a ``water of
the United States'' and is not excluded under paragraph (b)(3) even
where it has been ditched, channelized, or concreted.
    A ditch that relocates a stream is not an excluded ditch under
paragraph (b)(3), and a stream is relocated either when at least a
portion of its original channel has been physically moved, or when the
majority of its flow has been redirected. A ditch that is a relocated
stream is distinguishable from a ditch that withdraws water from a
stream without changing the stream's aquatic character. The latter type
of ditch is excluded from jurisdiction where it meets the listed
characteristics of excluded ditches under paragraph (b)(3). Agency
staff can determine historical presence of tributaries using a variety
of resources, such as historical maps, historic aerial photographs,
local surface water management plans, street

maintenance data, wetlands and conservation programs and plans, as well
as functional assessments and monitoring efforts. A ditch with
intermittent flow that drains a wetland and otherwise meets the
definition of ``tributary'' is a ``tributary'' and is not excluded
under paragraph (b)(3). See IV.I. below.
    Evidence, such as current or historic photographs, prior
delineations, or USGS, state and local topographic maps, may be used to
determine whether a ditch is an excluded ditch. Site characteristics
may also be present to inform the determination of whether the water
body is a ditch, such as shape, sinuosity, flow indications, etc., as
ditches are often created in a linear fashion with little sinuosity and
may or may not connect to another ``water of the United States.''
2. What changes did the Agencies make from the proposed rule based on
public comments?
    The rule's definition of ``tributary'' retains many elements from
the proposed rule, but reflects public comments in several important
ways. In particular, the rule emphasizes flow. The rule defines
``tributary'' by emphasizing physical characteristics created by water
flow and requiring that the water contributes flow, either directly or
through another water, to a traditional navigable water, interstate
water, or the territorial seas. The rule also is clearer regarding the
jurisdictional status of certain ditches, and clarifies that wetlands
and waters such as ponds and lakes that contribute flow to a
traditional navigable water, interstate water, or the territorial seas
but typically lack a bed and banks and ordinary high water mark are
considered ``adjacent'' but not a ``tributary.''
    A number of commenters suggested that the agencies should exclude
ephemeral streams from the definition of tributary, expressing concern
that ephemeral waters that flow very rarely would be considered a
jurisdictional tributary. The rule definition of ``tributary'' requires
that flow must be of sufficient volume, frequency, and duration to
create the physical characteristics of bed and banks and an ordinary
high water mark. If a water lacks sufficient flow to create such
characteristics, it is not considered a ``tributary'' under this rule.
While some commenters expressed concern that a feature that flowed very
rarely could meet the proposed definition of ``tributary,'' it is the
agencies' judgment that such a feature is not a tributary under the
rule because it would not form the physical indicators required under
the definitions of ``ordinary high water mark'' and ``tributary.''
    The rule includes ephemeral streams that meet the definition of
tributary as ``waters of the United States'' because the agencies
determined that such streams provide important functions for downstream
waters, and in combination with other covered tributaries in a
watershed significantly affect the chemical, physical, and biological
integrity of traditional navigable waters, interstate waters, and the
territorial seas. As noted by the SAB, and consistent with the
scientific literature, tributaries as a group exert strong influence on
the chemical, physical, and biological integrity of downstream waters,
even though the degree of connectivity is a function of variation in
the frequency, duration, magnitude, predictability, and consequences of
chemical, physical, and biological processes. See, e.g., SAB 2014b.
These significant effects on traditional navigable waters, interstate
waters, and the territorial seas occur even when the tributary is
small, intermittent, or ephemeral.
    In addition, the Science Report concludes that, ``[a]lthough less
abundant, the available evidence for connectivity and downstream
effects of ephemeral streams was strong and compelling, particularly in
context with the large body of evidence supporting the physical
connectivity and cumulative effects of channelized flows that form and
maintain stream networks.'' Science Report at 6-13. For example,
ephemeral headwater streams shape river channels in traditional
navigable or interstate waters by accumulating and gradually or
episodically releasing stored materials such as sediment and large
woody debris. These materials help structure traditional navigable and
interstate river channels by slowing the flow of water through channels
and providing substrate and habitat for aquatic organisms.
    Moreover, the agencies have historically considered ephemeral
tributaries to be ``waters of the United States.'' For example, for
many years EPA has reviewed and approved state water quality standards
for ephemeral waters under CWA section 303(c), several Corps'
Nationwide Permits under CWA section 404 address discharges of dredged
or fill material into ephemeral waters, and the agencies' definition of
``waters of the United States'' prior to this rule included all
tributaries without reference to flow regime.
    Numerous commenters asked that the final rule define ``bed and
banks,'' which are physical characteristics called for under the
definition of tributary. Such commenters emphasized the importance of a
definition of ``bed and banks,'' and some suggested definitional
language. To increase clarity, the preamble in IV.F.1. above includes a
definition of bed and banks adapted largely from longstanding agencies'
practice as well as comments. Several commenters suggested that the
rule should add a definition of ``ordinary high water mark.'' In
response and to increase clarity, the rule adds the Corps' existing
regulatory ordinary high water mark definition to EPA's regulations.
Corps technical manuals are available to help identify ordinary high
water mark, referenced above. Several commenters suggested that the
agencies not require a tributary to have both bed and banks and
ordinary high water mark, because bed and banks are themselves an
indicator of ordinary high water mark, and because ordinary high water
mark alone is an appropriate criterion for many streams in the arid
west where the characteristic of bed and banks is less common. The
agencies based their significant nexus determination for the covered
tributaries in part on the amount of flow indicated where a tributary
has both a bed banks and another indicator of ordinary high water mark,
so the rule continues to require both physical indicators with the
preamble at IV.F.1. above clarifying the means to conclude that those
indicators exist.
    Several commenters suggested that the rule exclude all constructed
waters from the definition of ``waters of the United States.'' While
the rule does exclude several types of constructed waters from
jurisdiction, it continues to consider constructed tributaries as
jurisdictional unless expressly excluded in paragraph (b) for the
reasons described in section IV.I. and the Technical Support Document.
    Many comments recommended that wetlands, ponds, and lakes that
contribute flow to a traditional navigable water, interstate water, or
the territorial seas but lack a bed and banks and ordinary high water
mark not be considered as tributaries, because of the importance of
those physical characteristics to the definition. Wetlands typically
lack bed and banks and ordinary high water mark, while lakes and ponds
typically have an ordinary high water mark and a bed but may lack
banks. The proposed rule expressly sought comment on whether such
waters should be considered as tributaries or as ``adjacent waters,''
recognizing that it might add an element of uncertainty to the
definition of

``tributary'' to include waters that lacked the physical features
called for in the definition. In addition, the SAB commented that
tributaries are not typically defined to include lentic systems (still
waters), and suggested that the agencies reconsider including ponds,
lakes, and wetlands as covered adjacent waters instead of tributaries.
SAB 2014b at 2. In response, the rule does not consider these waters to
be tributaries, but defines covered adjacent waters to include
wetlands, lakes, and ponds that connect segments of tributaries or are
at the head of the tributary system. See section G for further
discussion.

G. Adjacent Waters

    Section III above explains the basis for the agencies' conclusion
that covered adjacent waters have a significant nexus with
traditionally navigable waters, interstate waters, or the territorial
seas. The adjacency provision is based on the best available science,
intent of the CWA, and case law, and is consistent with the experience
of the agencies in making case-specific significant nexus
determinations. As discussed above in Section III, the SAB concludes,
``[t]he available science supports [the agencies'] proposal to include
adjacent waters and wetlands as waters of the United States.'' SAB
2014b at 2. This section describes the provisions of the rule governing
adjacent waters, changes made to the adjacent waters provision based on
comments on the proposed rule, and, finally, how science and the law
support the agencies' conclusions in the final rule.
1. What are the provisions of the rule?
    Under the rule, ``adjacent'' means bordering, contiguous, or
neighboring, including waters separated from other ``waters of the
United States'' by constructed dikes or barriers, natural river berms,
beach dunes, and the like. Waters adjacent to a traditional navigable
water, interstate water, territorial sea, impoundment, or tributary,
are ``waters of the United States.'' For purposes of adjacency, an
adjacent water includes wetlands within or abutting its ordinary high
water mark. Adjacency is not limited to waters located laterally to a
traditional navigable water, interstate water, the territorial seas, an
impoundment, or a tributary. Therefore, waters that connect segments of
a traditional navigable water, interstate water, the territorial seas,
an impoundment, or a tributary or are located at the head of a
traditional navigable water, interstate water, the territorial seas, an
impoundment, or a tributary may be determined to be bordering,
contiguous, or neighboring, and thus adjacent. ``Adjacent waters''
include wetlands, ponds, lakes, oxbows, impoundments, and similar water
features. ``Adjacent waters'' do not include any water excluded under
paragraph (b) of the rule. Note also that a water that does not meet
the definition of ``adjacent waters'' may be determined to be a ``water
of the United States'' on a case-specific basis under paragraph (a)(8)
of the rule.
    Within the definition of ``adjacent,'' the terms bordering and
contiguous are well understood, and for continuity and clarity the
agencies continue to interpret and implement those terms consistent
with the current policy and practice. Waters separated by a berm or
other similar feature remain ``adjacent'' under the definition.
    Some waters included under the definition of ``tributary'' in the
proposed rule, after consideration of public comment, are ``adjacent''
in the final rule. Specifically, waters that connect segments of, or
are at the head of, a traditional navigable water, interstate water,
the territorial seas, an impoundment, or a tributary are adjacent to
that water. For example, a pond that is the source water to a tributary
and borders the tributary at its uppermost reach is jurisdictional as
an adjacent water. Further, the rule states that an adjacent water
includes wetlands within or abutting its ordinary high water mark. This
language is designed to ensure that if there is a fringe wetland
abutting that pond that is the source water to a tributary, that
wetland is considered part of the pond under the rule and such pond as
a whole, including any abutting wetlands, is jurisdictional as an
adjacent water.
    For purposes of adjacency, including all three provisions of the
definition of ``neighboring,'' the entire water is adjacent if any part
of the water is bordering, contiguous or neighboring. Therefore, the
entire wetland is ``adjacent'' if any part of it is within the distance
thresholds established in the definition of ``neighboring.'' For
example, if a tributary has a 1,000 foot wide 100-year floodplain, then
a water that is located within 1,000 feet of the ordinary high water
mark of a covered tributary and extends to 2,000 feet is jurisdictional
in its entirety as ``neighboring.'' In addition, for purposes of
determining whether a water is ``adjacent'' artificial features (such
as roads) do not divide a water; rather, the water is treated as one
entire water.
    The definition of ``adjacent'' in the rule does not include those
waters in which established, normal farming, silviculture, and ranching
activities occur. Wetlands and farm ponds in which normal farming
activities occur, as those terms are used in section 404(f) of the
Clean Water Act and its implementing regulations, are not
jurisdictional under the Act as an ``adjacent'' water. Waters in which
normal farming, ranching, and silviculture activities occur instead
will continue to be subject to case-specific review, as they are today.
These waters may be determined to have a significant nexus on a case-
specific basis under paragraph (a)(7) or (a)(8). Recognizing the vital
role of farmers in providing the nation with food, fiber, and fuel, the
Clean Water Act in Section 404(f) exempts many normal farming
activities such as seeding, harvesting, cultivating, planting, soil and
water conservation practices, and other activities from the Section 404
permitting requirement. ``Normal'' farming, ranching, and silviculture
is clarified in the agencies' implementing regulations to mean
established and ongoing activities to distinguish from activities
needed to convert an area to farming, silviculture, or ranching and
activities that convert a water to a non-water. 40 CFR 232.3(c)(1). The
rule reflects this framework by clarifying the waters in which the
activities Congress exempted under Section 404(f) occur are not
jurisdictional as ``adjacent.'' It is important to recognize that
``tributaries,'' including those ditches that meet the tributary
definition, are not ``adjacent'' waters and are jurisdictional by rule.
    This provision interprets the intent of Congress and reflects the
intent of the agencies to minimize potential regulatory burdens on the
nation's agriculture community, and recognizes the work of farmers to
protect and conserve natural resources and water quality on
agricultural lands. While waters in which normal farming, silviculture,
or ranching practices occur may be determined to significantly affect
the chemical, physical, or biological integrity of downstream navigable
waters, the agencies believe that such determination should be made
based on a case-specific basis instead of by rule. The agencies also
recognize that waters in which normal farming, silviculture, or
ranching practices occur are often associated with modifications and
alterations including drainage, changes to vegetation, and other
disturbances the agencies believe should be specifically considered in
making a significant nexus determination.
    The rule establishes a definition of ``neighboring'' for purposes
of determining adjacency. In the rule, the

agencies identify three circumstances under which waters would be
``neighboring'' and therefore ``waters of the United States.''
    First, the term ``neighboring'' includes all waters located in
whole or in part within 100 feet of the ordinary high water mark of a
traditional navigable water, interstate water, the territorial seas, an
impoundment, or a covered tributary.
    Second, the term ``neighboring'' includes all waters within the
100-year floodplain of a traditional navigable water, interstate water,
the territorial seas, an impoundment, or a covered tributary that is
located in whole or in part within 1,500 feet of the ordinary high
water mark of that jurisdictional water. In this rule, the agencies
interpret ``100-year floodplain'' to mean ``the area that will be
inundated by the flood event having a one percent chance of being
equaled or exceeded in any given year.'' This is consistent with the
Federal Emergency Management Agency's (FEMA) definition of ``100-year
flood.'' If the 100-year floodplain is greater than 1,500 feet from the
ordinary high water mark, only those waters that are located in whole
or in part within 1,500 feet of the ordinary high water mark are
``neighboring.'' In addition, if the 100-year floodplain is less than
1,500 feet from the ordinary high water mark, only those waters located
in whole or in part within the floodplain are ``neighboring'' under
this provision.
    Third, the rule defines ``neighboring'' to include all waters
located in whole or in part within 1,500 feet of the high tide line of
a traditional navigable water or the territorial seas, and all waters
located within 1,500 feet of the ordinary high water mark of the Great
Lakes. This provision defines waters that begin within 1,500 feet of a
tidally-influence traditional navigable water or the territorial seas
and waters within 1,500 feet of the ordinary high water mark of the
Great Lakes as ``waters of the United States.'' To provide clarity for
this aspect of the definition, the agencies incorporated the Corps'
existing definition of high tide line into EPA's regulations at
paragraph (c)(7) in the rule.
    As noted above, the rule provides that with respect to the
boundaries for covered adjacent waters the entire water is
jurisdictional as long as the water is at least partially located
within the distance threshold, and the agencies interpret the rule to
apply to any single water or wetland that may straddle a distance
threshold. Low-centered polygonal tundra and patterned ground bogs
(also called strangmoor, string bogs, or patterned ground fens) are
considered a single water for purposes of the rule because their small,
intermingled wetland and non-wetland components are physically and
functionally integrated. These areas often have complex micro-
topography with repeated small changes in elevation occurring over
short distances. Science demonstrates that these wetlands function as a
single wetland matrix having clearly hydrophytic vegetation, hydric
soils, and wetland hydrology. As a result, the agencies will continue
to evaluate these wetlands as a single water under the rule. Where any
portion of these wetland types is bordering, contiguous or neighboring,
the entire wetland is a ``water of the United States.'' Similarly, for
purposes of a case-specific determination under paragraph (a)(8),
wetlands of these types constitute a single water when making a
significant nexus determination. Other wetlands may also have
intermingled wetland and non-wetland components that are so physically
and functionally integrated they can be considered a single water for
purposes of the rule. Groups of wetlands that are simply part of a
complex of wetlands would not be considered a single water for purposes
of the rule.
    The final rule also makes some ministerial changes to the
definition of ``adjacent.'' The existing regulation defined
``adjacent'' to mean ``bordering, contiguous, or neighboring,'' and had
a second sentence that clarified that wetlands separated by berms and
the like remain adjacent wetlands. The final rule combines those
sentences without changing the scope of adjacency.
    When determining the jurisdictional boundaries under the CWA for
``adjacent waters,'' the agencies will rely on published FEMA Flood
Zone Maps to identify the location and extent of the 100-year
floodplain. https://msc.fema.gov/portal. These maps are publicly
available and provide a readily accessible and transparent tool for the
public and agencies to use in locating the 100-year floodplain. It is
important to recognize, however, that much of the United States has not
been mapped by FEMA and, in some cases, a particular map may be out of
date and may not accurately represent existing circumstances on the
ground. The agencies will determine if a particular map is no longer
accurate based on factors, such as streams or rivers moving out of
their channels with associated changes in the location of the
floodplain. In the absence of applicable FEMA maps, or in circumstances
where an existing FEMA map is deemed by the agencies to be out of date,
the agencies will rely on other available tools to identify the 100-
year floodplain, including other Federal, State, or local floodplain
maps, Natural Resources Conservation Service (NRCS) Soil Surveys
(Flooding Frequency Classes), tidal gage data, and site-specific
modeling (e.g., Hydrologic Engineering Centers River System Analysis
System or HEC-RAS). http://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm and HEC-RAS and http://www.hec.usace.army.mil/software/hec-ras/. Additional supporting information can include historical
evidence, such as photographs, prior delineations, topographic maps,
and existing site characteristics. Because identifying the 100-year
floodplain is an important aspect of establishing jurisdiction under
the rule and the reliable and appropriate tools for identifying the
100-year floodplain may vary, the agencies will coordinate with other
federal and state agencies to develop additional information for EPA
and Corps field staff to further improve tools for identifying the 100-
year floodplain in a consistent, predictable, and scientifically valid
manner.
    When determining the outer distance threshold for an ``adjacent
water'' the line is drawn perpendicular to the ordinary high water mark
or high tide line of the traditional navigable water, interstate water,
the territorial seas, impoundment, or covered tributary and extended
landward from that point. If there are breaks in the ordinary high
water mark, the line should be extrapolated from the point where the
ordinary high water mark is observed on the downstream side to the
point where the ordinary high water mark is lost on the upstream side.
Therefore, waters may meet the definition of neighboring even where,
for example, a tributary temporarily flows underground.
    The agencies emphasize that they fully support efforts by States
and tribes to protect under their own laws any additional waters,
including locally special waters that may not be within the Federal
protections of the CWA as the agencies have interpreted its scope in
this rule. In promulgating the adjacent water boundaries, the agencies
have balanced protection and clarity, scientific uncertainties and
regulatory experience, and established boundaries that are, in their
judgment, reasonable and consistent with the statute and its goals and
objectives.
    If waters identified in this section are determined to be adjacent,
no case-specific significant nexus evaluation is required.

2. What changes did the agencies make from the proposed rule based on
public comments?
    In the proposal, the agencies sought comment on a number of ways to
address and clarify jurisdiction over ``adjacent waters,'' including
establishing a floodplain interval and providing clarity on reasonable
proximity as an important aspect of adjacency. In light of the
comments, the science, the agencies' experience, and the Supreme
Court's consistent recognition of the agencies' discretion to interpret
the bounds of CWA jurisdiction, the agencies have made some revisions
in the final rule designed to more clearly establish boundaries on the
scope of ``adjacent waters.''
    Under the proposal and the final rule, ``adjacent waters'' are
jurisdictional based on the conclusion that they have a significant
nexus to traditional navigable waters, interstate waters, or the
territorial seas, and there is no need for additional analysis. Some
commenters wanted a case-specific analysis for all ``adjacent waters''
as they believed that the waters would not individually have a
significant nexus to an adjacent ``water of the United States,'' while
others noted that their functional relationship to the downstream
traditional navigable waters, interstate waters, or the territorial
seas warranted the conclusion that they were all jurisdictional. Based
on a review of the science, the agencies' expertise and experience, and
the law, the agencies determined that ``adjacent waters,'' as defined,
alone or in combination with other covered ``adjacent waters'' in a
watershed have a significant nexus to a traditional navigable water,
interstate water or the territorial seas and therefore are ``waters of
the United States'' without the need for any additional analysis.
However, the rule also provides for case-specific analysis of some
waters that do not meet the definition of ``neighboring'' established
by the rule. See section IV.H.
    The proposal included wetlands, ponds, lakes, and impoundments that
contribute flow, directly or indirectly, to the downstream traditional
navigable waters, interstate waters, or the territorial seas in the
definition of ``tributary.'' Some commenters expressed concern that
since such waters generally do not have both an ordinary high water
mark and a bed and banks, the definition of tributary was contradictory
and confusing. The agencies sought comment on whether to treat these
waters as ``adjacent waters'' instead of tributaries, since they not
only contribute flow, but they also border or are contiguous to the
waters to which they contribute flow. The SAB in particular commented
that the agencies ``may want to consider whether flow-through lentic
systems should be included as ``adjacent waters'' and wetlands, rather
than as tributaries.'' SAB 2014b at 2. In light of the comments and to
provide additional clarity, the agencies revised the definitions of
``adjacent'' and ``tributary'' to include these waters as ``adjacent.''
    Under the existing rule, there is no definition for the term
``neighboring,'' and the public commented that not having a definition
created a lack of clarity and inconsistent field practices across the
nation. In the proposal, ``neighboring'' was defined to include waters
located within the riparian area or floodplain of a traditional
navigable water, interstate water, territorial sea, impoundment, or
tributary; waters with a shallow subsurface hydrologic connection to a
jurisdictional water; and waters with a confined surface hydrologic
connection to a jurisdictional water. Although the definitions were
scientifically-based for the terms ``riparian area'' and ``floodplain''
to define the lateral reach of the term ``neighboring,'' some
commenters indicated that the proposed definitions to clarify
neighboring were not clear. Those commenters requested that a specific
floodplain interval or other limitation should be established to more
clearly identify the outer limit of neighboring. Some commenters stated
that the proposed definition of ``neighboring'' was unclear, while
other commenters found the definition helped clarify CWA jurisdiction
and were supportive of including a broad definition, based on
ecological interconnectedness.
    Some commenters stated that the proposed definitions of ``riparian
area'' and ``floodplain'' were vague or ambiguous, broad or effectively
limitless, beyond the agencies' authority or difficult or impossible to
implement in the field. Other commenters were supportive of using the
riparian area as a basis for adjacency. Some commenters asked why the
agencies were proposing a new definition of ``floodplain'' that was
inconsistent with the definition used by other Federal agencies like
NRCS or FEMA. Some commenters suggested that if the agencies use
floodplains as a means to define ``neighboring,'' it should be limited
to the area inundated by the 2-year, 5-year, 10-year, or 20-year flood,
while other commenters supported the use of the 100-year floodplain as
a component of ``neighboring.'' Some commenters supported including all
wetlands and other waters in the 100-year floodplain as categorically
jurisdictional. Other commenters requested that floodplain size be
based on tributary size, while others suggested that it should be based
on soil and geologic features, and some suggested the use of the FEMA
flood zone maps. Some commenters stated that ``reasonable proximity''
was neither defined nor clarified adjacency, noting that adjacency
should not apply to waters separated from a ``water of the United
States'' by great distances.
    In response to comments and to provide greater clarity and
consistency, in the rule the agencies establish a definition of
neighboring which provides additional specificity requested by some
commenters, including establishing a floodplain interval and providing
specific boundaries from traditional navigable waters, interstate
waters, the territorial seas, impoundments, and tributaries. In the
proposal, the agencies requested comment on whether the rule should
provide greater specificity with regard to how the agencies will
determine if a water is located in the floodplain of a jurisdictional
water. 79 FR 22209. As recommended by the public and based on science,
the agencies' boundaries for ``neighboring'' are based largely on use
of the 100-year floodplain. The agencies concluded that the use of the
riparian area was unnecessarily complicated and that as a general
matter, waters in the riparian area will also be in the 100-year
floodplain. Further, should the riparian area on occasion extend beyond
the 100-year floodplain, the agencies have the ability to perform a
case-specific significant nexus analysis on a water out to 4,000 feet
from the ordinary high water mark or high tide line of a traditional
navigable water, interstate water, the territorial sea, impoundment, or
tributary. The agencies have drawn these lines based on their technical
expertise and experience in order to provide a rule that is practical
to understand and implement and protects those waters that
significantly affect the chemical, physical, or biological integrity of
traditional navigable waters, interstate waters, or the territorial
seas. Because science indicates that connectivity is on a gradient, the
agencies have also identified limited circumstances in which waters
that do not meet the definition of ``neighboring'' may be determined on
a case-specific basis to have a significant nexus. See section IV.I.
    First, the rule establishes as ``neighboring'' waters that occur
within 100 feet from traditional navigable

waters, interstate waters, the territorial seas, impoundments, and
tributaries.
    Second, the rule utilizes a specific floodplain and also
establishes maximum distances for purposes of ``neighboring.'' Studies
have found that waters within the floodplain are dynamically connected
and frequently interact with the downstream traditional navigable
water, interstate water, territorial sea, impoundment, or tributary.
Some commenters indicated that a specific floodplain or other
designation should be set to define the outer boundary of
``neighboring.'' Further, some commenters requested that the 100-year
floodplain designation be used to define the outer boundary of
adjacency because the public understands this concept. Several
commenters recommended that FEMA or NRCS maps be used to support the
analysis as these maps are easily accessible to the public. Because
FEMA maps exist for many areas of the country and the NRCS Soil Survey
maps do as well, the agencies decided that defining ``neighboring''
based in part on a particular floodplain or recurrence interval was a
reasonable means of ensuring the consistency and certainty that is
important to the public and for implementation of the CWA. In drawing
lines, the agencies chose the 100-year floodplain in part because FEMA
and NRCS together have generally mapped large portions of the United
States, and these maps are publicly available, well-known and well-
understood.
    Because the 100-year floodplain can be very wide in some areas of
the country, particularly near large rivers, the agencies chose to
provide increased clarity and certainty while ensuring that waters that
provide important functions significantly affecting the chemical,
physical, and biological integrity of the downstream traditional
navigable waters, interstate waters, or the territorial seas are
protected by establishing a 1,500 foot maximum distance for neighboring
waters in the rule. Waters within the 100-year floodplain to a maximum
of 1,500 feet of the ordinary high water mark are adjacent without
regard to the presence of berms or other barriers. However, because the
science demonstrates that floodplain waters provide important functions
for downstream waters, the agencies have established a provision under
paragraph (a)(8) for case-specific significant nexus evaluations of
waters located in the 100-year floodplain of a traditional navigable
water, interstate water, or the territorial seas beyond 1,500 feet.
    The rule also establishes a separate bright line for including as
jurisdictional those waters that occur within 1,500 feet of tidally-
influenced traditional navigable waters or the territorial seas.
    The proposal defined ``neighboring'' to include waters with a
surface connection to jurisdictional waters and some commenters
recommended eliminating surface hydrologic connectivity as a basis for
adjacency. The definition of neighboring does not include a provision
defining ``neighboring'' based on a surface hydrologic connection.
However, waters with confined surface hydrologic connections are
considered adjacent where they are bordering, contiguous, or
neighboring a traditional navigable water, interstate water, the
territorial seas, impoundment, or covered tributary. For example, a
water with a confined surface hydrologic connection to a traditional
navigable water that is 1,200 feet from the high tide line of that
water would meet the definition of neighboring and be considered an
adjacent water. In circumstances where a water does not meet the
definition of neighboring but is located within the 100-year floodplain
of a traditional navigable water, interstate water, or the territorial
seas, or within 4,000 feet of a jurisdictional water, a confined
surface hydrologic connection may be an important factor in evaluating
a case-specific significant nexus under paragraph (a)(8). See section
H. below.
    The proposal defined ``neighboring'' to include waters connected
with a shallow subsurface connection, and some commenters recommended
eliminating subsurface hydrologic connectivity as a basis for
adjacency. For example, some commenters asserted that, because the CWA
does not apply to groundwater, the agencies do not have the authority
to assert jurisdiction over waters connected to other ``waters of the
United States'' via a shallow subsurface hydrologic connection. Some
commenters were concerned that the distinction between ``groundwater''
and a ``shallow subsurface connection'' was unclear and questioned
whether using a shallow subsurface connection as a basis for adjacency
is contradictory to excluding groundwater--including groundwater
drained through subsurface drainage systems--as a ``water of the United
States.'' Some commenters supported use of shallow subsurface
connectivity for adjacency, since the significant nexus test would be
employed to make the determination of jurisdiction. Several commenters
suggested that the rule should protect groundwater and shallow
subsurface flow, due to its connectivity to other ``waters of the
United States'' and particularly since altering it could affect the
downstream waters. A few commenters simply requested clarifications
regarding issues such as how to determine whether a subsurface
connection exists; the meaning of ``shallow;'' distinguishing between
``shallow'' and ``deep;'' whether there were any boundaries on
adjacency via hydrologic connectivity; and determining whether the
connection was ``sufficient'' to establish adjacency. In order to
provide more certainty to the public, the rule does not include a
provision defining neighboring based on shallow subsurface flow, though
such flow may be an important factor in evaluating a water on a case-
specific basis under paragraph (a)(8), as appropriate.
    Some commenters expressed concern that the agencies' proposed
definition of ``neighboring,'' ``riparian area,'' and ``floodplain''
would mean that all land within the floodplain or riparian area would
become regulated. In fact, only waters, not land, in the floodplain or
riparian area would have been considered adjacent under the proposed
rule. Similarly, under the final rule, only waters, not land, are
adjacent. In response, the agencies have eliminated the definitions of
floodplain and riparian area and have provided a definition of
neighboring which is clear that only waters in specified circumstances
may be ``waters of the United States.''
    The agencies also eliminated a parenthetical from the existing
``adjacent wetlands'' regulatory provision. The phrase ``other than
waters that are themselves wetlands'' was intended to preclude
asserting CWA jurisdiction over wetlands that were simply adjacent to a
non-jurisdictional wetland. Such waters do not meet the definition of
``adjacent'' under the rule since waters must be adjacent to a
traditional navigable water, interstate water, the territorial seas,
impoundment, or covered tributary, so the phrase is unnecessary and
confusing. With this change, the agencies are protecting all waters
that meet the definition of ``adjacent'' as ``waters of the United
States,'' and eliminating confusion caused by the parenthetical. For
example, where the 100-year floodplain is greater than 1,500 feet, all
wetlands within 1,500 feet of the tributary's ordinary high water mark
are jurisdictional because they are ``neighboring'' to the tributary,
regardless of the wetlands' position relative to each other.
    Some commenters stated that the proposed rule was an expansion of
jurisdiction because it would change the

provision from ``adjacent wetlands'' to ``adjacent waters.'' The
agencies acknowledge that under the existing regulation, the adjacency
provision applied only to wetlands adjacent to ``waters of the United
States.'' However, also under the existing regulation, ``other waters''
(such as intrastate rivers, lakes and wetlands that are not otherwise
jurisdictional under other sections of the rule) could be determined to
be jurisdictional if the use, degradation or destruction of the water
could affect interstate or foreign commerce. This provision of the
existing regulation reflected the agencies' interpretation at the time
of the jurisdiction of the CWA to extend to the maximum extent
permissible under the Commerce Clause of the Constitution. Therefore,
while the language of the specific adjacency provision in the final
rule may have changed from wetlands to waters, that does not represent
an expansion of jurisdiction as a whole in comparison to the existing
regulation, since adjacent non-wetland waters would have been subject
to jurisdiction under the ``other waters'' provision. The final rule
does not protect all waters that were protected under the ``other
waters'' provision of the existing regulation, and therefore the
inclusion of adjacent ponds, for example, in the ``adjacent waters''
provision of the final rule does not reflect an overall expansion of
jurisdiction when compared to the existing regulation.
3. How do science and law support the rule?
    Based on a review of the scientific literature and the agencies'
expertise and experience the agencies determined that the categories of
waters discussed below are integrally linked to the chemical, physical,
or biological functions of waters to which they are adjacent and
downstream to the traditional navigable waters, interstate waters or
the territorial seas. Therefore, the agencies determined that the
waters defined as adjacent have a significant nexus with traditional
navigable waters, interstate waters or the territorial seas and are
thus ``waters of the United States.'' Additional information, including
citations, can be found in section III of the preamble, the Science
Report, and the Technical Support Document for the rule.
a. Waters that are Bordering or Contiguous
    As discussed in section III above, wetlands, ponds, lakes, oxbows,
impoundments, and similar water features that are bordering or
contiguous perform a myriad of critical chemical and biological
functions associated with the downstream traditional navigable waters,
interstate waters, or the territorial seas. Such waters are integrally
linked with the jurisdictional waters to which they are adjacent.
Because of their close physical proximity to nearby jurisdictional
waters, bordering or contiguous waters readily exchange their waters
through the saturated soils surrounding the traditional navigable
water, interstate water, the territorial seas, impoundment, or covered
tributary or through surface exchange. This commingling of waters
allows bordering or contiguous waters to both provide chemically
transformed waters to streams and to absorb excess stream flow, which
in turn can significantly affect downstream traditional navigable
waters, interstate waters, or the territorial seas. The close proximity
also allows for the direct exchange of biological materials, including
organic matter that serves as part of the food web of downstream
traditional navigable waters, interstate waters, or the territorial
seas. Waters that are bordering or contiguous are often located on the
floodplain or within the riparian area of the waters to which they are
adjacent. Bordering or contiguous waters include those that directly
abut a traditional navigable water, interstate water, the territorial
seas, impoundment, or covered tributary. The Science Report and the
Technical Support Document demonstrate that such waters are physically,
chemically, and biologically integrated with downstream traditional
navigable waters, interstate waters, or the territorial seas and
significantly affect their integrity.
b. Waters Separated From Other ``Waters of the United States'' by
Constructed Dikes or Barriers, Natural River Berms, Beach Dunes and the
Like
    Adjacent waters separated from a traditional navigable water,
interstate water, the territorial seas, impoundment, or covered
tributary by constructed dikes or barriers, natural river berms, beach
dunes, and the like continue to have a significant effect on downstream
traditional navigable waters, interstate waters, or the territorial
seas, either alone or in combination with other ``adjacent waters.''
Such waters continue to have a hydrologic connection to downstream
waters. This is because constructed dikes or barriers, natural river
berms, beach dunes, and the like typically do not block all water flow.
This hydrologic connection can occur via seepage, or the flow of water
through the soil pores, or via over-topping, where water from the
nearby traditional navigable water, interstate water, the territorial
seas, impoundment, or covered tributary periodically overtops the berm
or other similar feature. Berm-like landforms known as natural levees
occur naturally and do not isolate adjacent wetlands from the streams
that form them. Natural levees and the wetlands and waters behind them
are part of the floodplain. Natural levees are discontinuous, which
allows for a hydrologic connection to the stream or river via openings
in the levees and thus the periodic mixing of river water and
backwater. Man-made levees and similar structures also do not isolate
``adjacent waters.'' Waters, including wetlands, separated from a
jurisdictional water by a natural or man-made berm serve many of the
same functions as other ``adjacent waters.'' Furthermore, even in cases
where a hydrologic connection may not exist, there are other important
considerations, such as chemical and biological functions, that result
in a significant nexus between the adjacent wetlands or waters and the
nearby ``waters of the United States,'' and traditional navigable
waters, interstate waters, or the territorial seas. On this point,
Justice Kennedy stated: ``In many cases, moreover, filling in wetlands
separated from another water by a berm can mean that floodwater,
impurities, or runoff that would have been stored or contained in the
wetlands will instead flow out to major waterways. With these concerns
in mind, the Corps' definition of adjacency is a reasonable one, for it
may be the absence of an interchange of waters prior to the dredge and
fill activity that makes protection of the wetlands critical to the
statutory scheme.'' Rapanos at 775. For instance, covered adjacent
waters behind berms can still serve important water quality functions,
serving to filter pollutants and sediment before they reach downstream
waters. Wetlands and open waters behind berms, where the system is
extensive, can help reduce the impacts of storm surges caused by
hurricanes. Such ``adjacent waters,'' including wetlands, separated
from waters by berms and the like maintain ecological connection with
those waters. It is not the existence of the dike, levee, and the like
that makes these waters jurisdictional. Adjacent waters separated from
the tributary network by constructed dikes or barriers, natural river
berms, beach dunes, and the like continue to have a hydrologic
connection to downstream waters.

Waters behind berms and the like can significantly affect the chemical,
physical, and biologic integrity of traditional navigable waters,
interstate waters, or the territorial seas.
c. Waters Within 100 Feet
    All wetlands, ponds, lakes, oxbows, impoundments, and similar water
features that are located in whole or in part within 100 feet of the
ordinary high water mark of a jurisdictional water perform a myriad of
critical chemical, physical, and biological functions associated with
the downstream traditional navigable water, interstate water or the
territorial seas and therefore the agencies have determined that they
are ``neighboring'' and thus ``waters of the United States.'' Waters
within 100 feet of a jurisdictional water are often located within the
riparian area and are often connected via surface and shallow
subsurface hydrology to the water to which they are adjacent. While the
SAB was clear that distance is not the only factor that influences
connections and their effects downstream, due to their close proximity
to jurisdictional waters, waters within 100 feet are often located
within a landscape position that allows for them to receive and process
surface and shallow subsurface flows before they reach streams and
rivers. These waters individually and collectively affect the integrity
of downstream waters by acting primarily as sinks that retain
floodwaters, sediments, nutrients, and contaminants that could
otherwise negatively impact the condition or function of downstream
waters. Wetlands and open waters within close proximity of
jurisdictional waters improve water quality through assimilation,
transformation, or sequestration of nutrients, sediment, and other
pollutants that can affect the integrity of downstream traditional
navigable waters, interstate waters, or the territorial seas. These
waters, including wetlands, also provide important habitat for aquatic-
associated species to forage, breed, and rest.
    In order to provide greater clarity and consistency and based on a
review of the science and the agencies' expertise and experience, the
agencies identified a 100 foot threshold for neighboring waters to a
traditional navigable water, interstate water, territorial sea,
tributary, or impoundment. Further, the agencies determined that there
is a significant nexus with the downstream traditional navigable
waters, interstate waters, or the territorial seas, and these
``adjacent waters'' are ``waters of the United States.'' With respect
to provision of water quality benefits downstream, non-floodplain
waters within close proximity of the stream network often are able to
have more water quality benefits than those located at a distance from
the stream. Many studies indicate that the primary water quality and
habitat benefits will generally occur within a several hundred foot
zone of a water. In addition, the scientific literature indicates that
to be effective, contaminant removal needs to occur at a reasonable
distance prior to entry into the downstream traditional navigable
waters, interstate waters, or the territorial seas. Some studies also
indicate that fish, amphibians (e.g., frogs, toads), reptiles (e.g.,
turtles), and small mammals (e.g., otters, beavers, etc.) will use at
least a 100 foot zone for foraging, breeding, nesting, and other life
cycle needs.
    Based on a review of the scientific literature and the agencies'
expertise and experience, there is clear evidence that the identified
waters within 100 feet of the ordinary high water mark of a
jurisdictional water, even when located outside the floodplain, perform
critical processes and functions discussed in section III above. All
waters within 100 feet of a jurisdictional water significantly affect
the chemical, physical, or biological integrity of the waters to which
they are adjacent, and those waters in turn significantly affect the
chemical, physical, or biological integrity of the downstream
traditional navigable waters, interstate waters, or the territorial
seas. The agencies established a 100 foot threshold from the water's
lateral limit in the definition of neighboring because, based on the
agencies' expertise and experience implementing the CWA and in light of
the science, the agencies concluded this was a reasonable and practical
boundary within which to conclude the waters clearly significantly
affected the integrity of traditional navigable waters, interstate
waters, or the territorial seas, and these ``adjacent waters'' are
``waters of the United States.''
d. Floodplain Waters Within 1,500 Feet
    As discussed in section III above, wetlands and open waters that
are neighboring perform a myriad of critical chemical and biological
functions associated with the downstream traditional navigable waters,
interstate waters, or the territorial seas. The scientific literature
supports that wetlands and open waters in floodplains are chemically,
physically, and biologically connected to downstream traditional
navigable waters, interstate waters, or the territorial seas and
significantly affect the integrity of such waters. The Science Report
concludes that wetlands and open waters located in ``floodplains are
physically, chemically and biologically integrated with rivers via
functions that improve downstream water quality, including the
temporary storage and deposition of channel-forming sediment and woody
debris, temporary storage of local ground water that supports baseflow
in rivers, and transformation and transport of stored organic matter.''
Science Report at ES-2 to ES-3. Such waters act as the most effective
buffer to protect downstream waters from nonpoint source pollution
(such as nitrogen and phosphorus), provide habitat for breeding fish
and aquatic insects that also live in streams, and retain floodwaters,
sediment, nutrients, and contaminants that could otherwise negatively
impact the condition or function of downstream waters.
    For waters in the 100-year floodplain within 1,500 feet of the
ordinary high water mark of a traditional navigable water, interstate
water, the territorial seas, impoundment, or covered tributary, the
agencies determine there is a significant nexus with the downstream
traditional navigable waters, interstate waters, or the territorial
seas and these waters are critical to protect the downstream waters.
Based on a review of the scientific literature, the agencies' technical
expertise and experience, and the implementation value of drawing clear
lines, the rule establishes a boundary for floodplain waters to meet
the definition of ``neighboring'' and be ``waters of the United
States'' by rule. This boundary was established in order to protect
vitally important waters within a watershed while at the same time
providing a practical and implementable rule. The agencies are not
determining that waters in the floodplain farther than 1,500 feet from
the ordinary high water mark never have a significant nexus. Rather,
the agencies are using their technical expertise to promulgate a
practical rule that draws reasonable boundaries in order to protect the
waters that most clearly have a significant nexus while minimizing
uncertainty about the scope of ``waters of the United States.'' Because
waters beyond these boundaries may have a significant nexus, the rule
also establishes areas in which a case-specific significant nexus
determination must be made. See section IV.H.
e. Waters Within 1,500 Feet of Tidally-Influenced Traditional Navigable
Waters or the Territorial Seas or the Great Lakes
    Many tidally-influenced waters do not have floodplains, so the
agencies

include a separate provision within the definition of ``neighboring''
to protect the ``adjacent'' waters that have a significant nexus to
tidally-influenced traditional navigable waters or the territorial seas
or the Great Lakes. Under Riverside Bayview and Justice Kennedy's
opinion in Rapanos, waters adjacent to traditional navigable waters,
including the territorial seas, are ``waters of the United States.''
Because the connection to a tidally-influenced traditional navigable
water, the territorial seas, or the Great Lakes is so close, the rule
defines ``neighboring'' to include waters within 1,500 feet of the high
tide line or the ordinary high water mark of the Great Lakes. Wetlands,
ponds, lakes, oxbows, impoundments, and similar water features within
1,500 feet of these waters are physically connected to such waters by
surface and shallow subsurface flow. As demonstrated in section III
above, these waters perform a myriad of critical chemical and
biological functions associated with these nearby waters to which they
are adjacent.
    These waters in combination significantly affect the integrity of
the connected tidally influenced traditional navigable water or the
territorial seas or the Great Lakes by acting primarily as sinks that
retain floodwaters, sediments, nutrients, and contaminants that could
otherwise negatively impact the condition or function of those waters.
Like floodplain waters, the scientific literature supports that
wetlands and other similar waters within close proximity improve water
quality through assimilation, transformation, or sequestration of
nutrients, sediment, and other pollutants that can affect downstream
water quality. These waters also provide important habitat for aquatic-
associated species to forage, breed, and rest in.
    For example, wetlands dominated by grass-like vegetation that occur
in depressional areas between sand dunes or beach ridges along the
territorial seas and the Great Lakes shoreline are dependent upon these
waters for their water source. The waters, including wetlands,
generally form when water levels of the territorial seas fall or the
Great Lakes drop, creating swales that support a diverse mix of wetland
vegetation and many endangered and threatened species. Many studies
demonstrate that these waters have been shown to act in concert with
the rising and lowering of the tide, and that the critical functions
provided by these waters are similar and play an important role in
maintaining the chemical, physical, or biological integrity of the
nearby traditional navigable waters, interstate waters, or the
territorial seas because of the hydrological and ecological connections
to and interactions with those waters.
    Science demonstrates that distance is a factor in the connectivity
and the strength of connectivity of wetlands and open waters to
downstream waters. Thus, waters that are more distant generally have
less opportunity to be connected to downstream waters. Wetlands and
open waters closer to the stream network generally will have greater
hydrologic and biological connectivity than waters located farther from
the same network. For instance, waters that are more closely proximate
have a greater opportunity to contribute flow. Via their hydrologic
connectivity, they also have chemical connectivity to and effects on
these downstream waters and are more likely to impact water quality due
to their close distance. Waters more closely located to these waters
are also more likely to be biologically connected to such waters more
frequently and by more species, including amphibians and other aquatic
animals. Because tidally-influenced traditional navigable waters, the
territorial seas, and the Great Lakes are generally much larger in size
than other jurisdictional waters, the agencies believe that a 1,500
foot threshold is a reasonable distance to capture most wetlands and
open waters that are so closely linked to these waters that they can
properly be considered adjacent as neighboring waters.
    Based on a review of the scientific literature and the agencies'
expertise and experience, there is clear evidence waters within 1,500
feet of these waters, even when located outside the floodplain, perform
critical processes and functions discussed in section III above. The
agencies established a 1,500 foot threshold from the water's lateral
limit, which would be either the high tide line or the ordinary high
water mark, in the definition of neighboring because, based on the
agencies' expertise and experience implementing the CWA and in light of
the science, the agencies concluded this was a reasonable and practical
boundary within which to conclude the waters most clearly significantly
affected the integrity of the traditional navigable water or the
territorial seas, and these covered adjacent waters are ``waters of the
United States.'' Waters located within the 100-year floodplain of a
traditional navigable water, interstate water, or the territorial seas,
and waters located more than 1,500 feet and less than 4,000 feet from
the ordinary high water mark of a traditional navigable water,
interstate water, the territorial seas, an impoundment, or a tributary,
may still be determined to have a significant nexus on a case-specific
basis under paragraph (a)(8) of the rule and therefore be a ``water of
the United States.'' See section IV.H.

H. Case-Specific ``Waters of the United States''

    The rule establishes two exclusive circumstances under which case-
specific determinations will be made for whether a water has a
``significant nexus'' and is therefore a ``water of the United
States.'' The proposed rule included a broad provision that allowed for
a case-specific determination of significant nexus for any water that
was not categorically jurisdictional or excluded. Many commenters
expressed concern that such a broad opportunity for case-specific
``waters of the United States'' determinations would lead to too much
uncertainty about the jurisdictional status of waters in broad areas
throughout the country. The agencies have greatly reduced the extent of
waters subject to this individual review by carefully incorporating the
scientific literature and by utilizing agency expertise and experience
to draw boundaries. The rule provides for case-specific determinations
under more narrowly targeted circumstances based on the agencies'
assessment of the importance of certain specified waters to the
chemical, physical, and biological integrity of traditional navigable
waters, interstate waters, and the territorial seas.
    First, the rule identifies at paragraph (a)(7) five subcategories
of waters (Prairie potholes, Carolina and Delmarva bays, pocosins,
western vernal pools in California, and Texas coastal prairie wetlands)
that the agencies have determined are ``similarly situated'' for
purposes of a significant nexus determination. Second, the rule
identifies at paragraph (a)(8) specific circumstances under which
waters will be subject to a case-specific significant nexus
determination but for which the agencies have not made a ``similarly
situated'' determination: Waters within the 100-year floodplain of a
traditional navigable water, interstate water, or the territorial seas,
and waters within 4,000 feet of the high tide line or the ordinary high
water mark of a traditional navigable water, interstate water, the
territorial seas, impoundments, or tributaries, as defined. If any
water meets the definition of ``adjacent'' waters it is jurisdictional