underground. Tributaries may temporarily flow underground in regions
with karst geology or lava tubes, for example, maintaining similar flow
characteristics underground and at the downstream point where they
return to the surface. The agencies will also continue their familiar
practice that a discontinuity in the OHWM also does not typically sever
jurisdiction upstream where the OHWM has been removed by development,
agriculture, or other land uses. For example, tributaries can be
relocated below ground to allow reasonable development to occur. In
urban areas, surface waters are often rerouted through an artificial
tunnel system to facilitate development. See, e.g., Science Report at
3-3, and sections III.A and IV.A.ii of the Technical Support Document.
Underground streams are distinct from groundwater due to their very
direct hydrologic connection to the portions of the tributaries that
are or re-surface above ground. Typically, groundwater connections
would be much slower than connections via underground streams.
Tributaries that have been rerouted underground are contained within a
tunnel system or other similar channelized subsurface feature, while
naturally occurring subterranean streams flow within natural conduits
like karst formations or lava tubes. The agencies will look for
indicators of flow both above and below the discontinuity. For example,
a discontinuity in the OHWM may exist due to constructed breaks (e.g.,
culverts, pipes, or dams) \98\ or natural breaks (e.g., debris piles or
boulder fields). Site specific conditions will continue to determine
the distance up the tributary network that is evaluated to see if the
feature creates a temporary break or if it severs the upstream
connection and constitutes the start of the tributary system.
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    \98\ Under past practice, the agencies have sometimes
characterized bridges as artificial breaks, such as under the 2015
Clean Water Rule. See 80 FR 37106 (June 29, 2015). However, bridges
do not necessarily create discontinuity in the OHWM, and the
agencies recognize that tributaries flowing under bridges may still
show evidence of an OHWM and in such circumstances would continue to
be jurisdictional where they meet either the relatively permanent or
significant nexus standard.

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    Under this rule, swales and erosional features (e.g., gullies,
small washes) characterized by low volume, infrequent, or short
duration flow are not tributaries and are not jurisdictional. See
section IV.C.7 of this preamble. Because swales and erosional features
were considered to be generally non-jurisdictional features under pre-
2015 practice, the agencies have extensive experience differentiating
between these features and tributaries on the landscape. See Rapanos
Guidance at 11-12. Streams are waterbodies that are typically
characterized by the presence of a channel and an OHWM, and lakes and
ponds are waterbodies that are also typically characterized by the
presence of an OHWM, in the absence of adjacent wetlands. In contrast,
erosional features like gullies and rills are typically more deeply
incised than streams and lack an OHWM. Similarly, swales do not have an
OHWM and typically lack a more defined channel that a stream exhibits.
See section IV.C.7 of this preamble and section III.A.v of the
Technical Support Document for additional discussion on how to
distinguish between tributaries, erosional features, and swales; see
section IV.A.ii of the Technical Support Document for additional
discussion on how to identify tributaries based on an OHWM.
    A variety of field and remote tools can be used to determine
whether a water is a tributary.\99\ Due to limitations associated with
some remote tools, field verification for accuracy may be necessary
(e.g., due to scale or vegetation cover, not all tributaries may be
visible in satellite imagery and aerial photographs or mapped in the
NHD). Examples of field indicators will be discussed in more detail
below.
---------------------------------------------------------------------------

    \99\ Direct observation or various remote sensing resources such
as USGS stream gage data (available at https://waterdata.usgs.gov/nwis/rt), USGS topographic maps (available at https://www.usgs.gov/the-national-map-data-delivery/topographic-maps), high-resolution
elevation data and associated derivatives (e.g., slope or curvature
metrics), Federal Emergency Management Agency (FEMA) flood zone maps
(available at https://msc.fema.gov/portal/home), NRCS soil maps
(available at https://websoilsurvey.sc.egov.usda.gov/App/WebSoilSurvey.aspx), National Hydrography Dataset (NHD) data,
National Wetlands Inventory (NWI) data, maps and geospatial datasets
from Tribal, State, or local governments, and/or aerial or satellite
imagery can also be used. Tributaries are often observable in aerial
imagery and high-resolution satellite imagery by their topographic
expression, characteristic linear and curvilinear patterns, dark
photographic tones, or the presence of riparian vegetation. USGS
topographic maps often include different symbols to indicate mapped
hydrographic features (see ``Topographic Map Symbols,'' available at
https://pubs.usgs.gov/gip/TopographicMapSymbols/topomapsymbols.pdf).
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(2) Identifying Whether the Water Is Part of the Tributary System of a
Paragraph (a)(1) Water
    The next step in determining whether a waterbody is a tributary is
to identify whether the waterbody is part of the tributary system of a
paragraph (a)(1) water. The tributary must flow directly or indirectly
through another water or waters to a traditional navigable water, the
territorial seas, or interstate water. Waters through which a tributary
may flow indirectly include, for example, impoundments, wetlands,
lakes, ponds, and streams. A tributary may flow through a number of
downstream waters, including non-jurisdictional features, such as a
ditch excluded under paragraph (b) of this rule or an excluded waste
treatment system, and jurisdictional waters that are not tributaries,
such as an adjacent wetland. But, the tributary must be part of a
tributary system that eventually flows to a traditional navigable
water, the territorial seas, or an interstate water to be
jurisdictional. A tributary may flow through another stream that flows
infrequently, and only in direct response to precipitation, and the
presence of that stream is sufficient to demonstrate that the tributary
flows to a paragraph (a)(1) water. Tributaries are not required to have
a surface flowpath all the way down to the paragraph (a)(1) water. For
example, tributaries can contribute flow through certain natural and
artificial breaks (including certain non-jurisdictional features), some
of which may involve subsurface flow as described above in section
IV.C.4.b of this preamble.
    In evaluating the flowpath from a water feature, the agencies can
use USGS maps; NWI data; Tribal, State, and local knowledge or maps;
dye tests, tracers, or other on the ground tests; field observations;
aerial photography; or other remote sensing information. The agencies
can also use available models, including models developed by Federal,
Tribal, State, and local governments, academia, and the regulated
community.\100\ These tools could be used in conjunction with field
observations, data, and other desktop tools to evaluate whether a
tributary flows directly or indirectly to a paragraph (a)(1) water. For
tributaries to paragraph (a)(2) impoundments, a flowpath to the
impoundment and to a paragraph (a)(1) water can be identified using
these same tools.
---------------------------------------------------------------------------

    \100\ One such model includes the USGS StreamStats ``Flow
(Raindrop) Path'' GIS tool which allows the user to click a point on
a map, after which a flowpath is drawn to estimate where water may
flow from that point to the stream network, eventually making its
way to the ocean if the tributary network allows for it available at
https://streamstats.usgs.gov/ss/. The StreamStats tool may
potentially be used to identify the flowpath from the subject waters
to the downstream paragraph (a)(1) water using the ``Flow (Raindrop)
Path'' component of the tool.
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ii. Determining Whether a Tributary Meets the Relatively Permanent
Standard
    Under this rule, tributaries that meet the relatively permanent
standard are jurisdictional under the Clean Water Act as ``waters of
the United States.'' In implementing the relatively permanent standard,
the agencies draw key concepts from the 2020 NWPR's interpretation, but
modify that rule's approach to ensure the term can be practically
implemented. Specifically, under this rule the relatively permanent
standard encompasses surface waters that have flowing or standing water
year-round or continuously during certain times of the year. Relatively
permanent waters do not include surface waters with flowing or standing
water for only a short duration in direct response to precipitation.
The approach in this rule would encompass tributaries considered
relatively permanent under the 2020 NWPR, as well as those considered
relatively permanent under the Rapanos Guidance, providing continuity
in approach for the regulated community and other stakeholders.
Tributaries that do not meet the relatively permanent standard must be
assessed under the significant nexus standard. See section IV.C.4.c.iii
of this preamble.
    The agencies' interpretation of relatively permanent tributaries to
include surface waters that have flowing or standing water year-round
or continuously during certain times of the year is consistent with the
Rapanos plurality's interpretation of ``waters of the United States.''
The Rapanos plurality interpreted ``waters of the United States'' as
encompassing ``relatively permanent, standing or continuously flowing
bodies of water,'' including streams, rivers, oceans, lakes, and other
bodies of waters that form geographical features. 547 U.S. at 739, 742.
The plurality noted that its reference to ``relatively permanent''
waters did ``not necessarily exclude streams, rivers, or lakes that
might dry up in extraordinary circumstances, such as drought,'' or
``seasonal rivers, which contain continuous flow during some months of
the year but no flow during dry months.'' Id. at 732 n.5 (emphasis in
original); see also 85 FR 22289 (April 21, 2020) (citing the same
language from the plurality in support of the 2020 NWPR's
interpretation of relatively permanent waters).

    The agencies have decided to implement this approach because it is
consistent with the Rapanos plurality opinion, it reflects and
accommodates regional differences in hydrology and water management,
and it can be implemented using available, easily accessible tools. It
will therefore be a straightforward approach for the agencies and the
regulated community to implement. In addition, maintaining an
interpretation that encompasses the tributaries considered relatively
permanent under the pre-2015 regulatory regime and the 2020 NWPR
addresses the many comments from stakeholders emphasizing the need for
clarity and certainty in the scope of ``waters of the United States.''
    ``Flowing water'' under this rule is meant to encompass not just
streams and rivers, but also lakes, ponds, and impoundments that are
part of the tributary system, as such waters outlet to the tributary
network and contribute flow downstream at the outlet point. In
addition, ``flowing water'' under this rule is meant to encompass those
tributaries that are frozen for parts of the year. Such tributaries
typically have flowing water underneath the frozen surface.
    The phrase ``certain times of the year'' is intended to include
extended periods of standing or continuously flowing water occurring in
the same geographic feature year after year, except in times of
drought. The defining characteristic of relatively permanent waters
with flowing or standing water continuously during only certain times
of the year is a temporary lack of surface flow, which may lead to
isolated pools or dry channels during certain periods of the year. The
phrase ``direct response to precipitation'' is intended to distinguish
between episodic periods of flow associated with discrete precipitation
events versus continuous flow for extended periods of time.
    A number of commenters suggested that the agencies interpret
relatively permanent tributaries to include those that flow year-round
or at least seasonally (e.g., typically three months), consistent with
the approach in the Rapanos Guidance. This rule encompasses tributaries
that are ``relatively permanent'' under the Rapanos Guidance. However,
the agencies have decided not to use the term ``seasonal'' from the
Rapanos Guidance for several reasons. First, the agencies have
determined that directly describing the scenarios in which waters would
be ``relatively permanent'' is clearer than using the term
``seasonal,'' the meaning of which can vary and could be misunderstood
to establish a specific required flow duration. See section
IV.C.4.c.ii.1 of this preamble for further discussion of the challenges
of requiring a specific flow duration. Relatively permanent flow may
occur seasonally, but the phrase is also intended to encompass
tributaries in which extended periods of standing or continuously
flowing water are not linked to naturally recurring annual or seasonal
cycles. Specifically, relatively permanent waters may include
tributaries in which flow is driven more by various water management
regimes and practices, such as tributaries with extensive flow
alteration (e.g., diversions, bypass channels, water transfers) and
effluent-dependent streams. For example, in areas of the West where
water withdrawals or groundwater pumping can substantially modify flow
characteristics, onset and cessation of streamflow in some tributaries
may be more closely tied to changes in water use associated with
irrigation than with seasons of the year. In such flow-altered
tributaries, streamflow may change abruptly throughout the year due to
adjustments in facility operations or may vary from year to year due to
changes in water rights or water management regimes. In addition,
tributaries that typically flow throughout the spring may run dry in
years following a drought while storage reservoirs are being refilled.
When evaluating these types of artificially manipulated regimes, the
agencies may consider information about the regular manipulation
schedule and may potentially consider other remote resources or on-site
information to assess flow frequency.
    Other commenters recommended defining relatively permanent
tributaries using the 2020 NWPR's terms ``perennial'' and
``intermittent.'' Relatively permanent tributaries under this rule
encompass tributaries that were jurisdictional under the 2020 NWPR.
However, the agencies have decided to explain directly the way that the
relatively permanent standard should be implemented, rather than
defining the phrase with these terms. As evidenced by the variety of
comments proposing definitions for ``perennial'' and ``intermittent,''
adding these terms to this rule could cause confusion and uncertainty.
Moreover, many definitions of intermittent incorporate ``seasonal''
flow, a concept that the agencies decided not to employ in this rule
for the reasons discussed above. Other definitions of ``perennial'' and
``intermittent'' that commenters suggested would require specific
sources of flow, which the agencies also decided not to establish in
this rule because such requirements cannot readily apply to
hydrologically altered waters, and for the reasons discussed in section
IV.C.4.c.ii.2 of this preamble.
    While this rule implements the scope of relatively permanent
tributaries consistent with the approach in the 2020 NWPR, it does not
retain the 2020 NWPR's requirement that the tributaries contribute
surface water flow to a paragraph (a)(1) water in a ``typical year.''
See 85 FR 22251 (April 21, 2020). The 2020 NWPR defined a ``typical
year'' as when ``precipitation and other climatic variables are within
the normal periodic range (e.g., seasonally, annually) for the
geographic area of the applicable aquatic resource based on a rolling
thirty-year period.'' As discussed in section IV.B.3 of this preamble
and section II.B.iv.1 of the Technical Support Document, the typical
year analysis proved difficult to implement and yielded arbitrary and
potentially outdated results. Moreover, it is not required by the
plurality opinion in Rapanos, which simply required a ``connect[ion]''
to paragraph (a)(1) waters. See 547 U.S. at 742 (describing a
```wate[r] of the United States''' as ``i.e., a relatively permanent
body of water connected to traditional interstate navigable waters'').
This rule's requirement that jurisdictional tributaries flow directly
or indirectly to downstream paragraph (a)(1) waters or paragraph (a)(2)
impoundments implements the plurality's ``connect[ion]'' requirement.
See also section IV.C.4.b of this preamble.
(1) Duration and Timing of Flow for Relatively Permanent Tributaries
    Many commenters recommended that the agencies establish a
particular flow duration for relatively permanent waters. Suggestions
ranged from a minimum of three months to 290 days. The agencies decided
not to establish a minimum duration because flow duration varies
extensively by region. Establishing a uniform number equally applicable
to the deserts in the arid West, the Great Lakes region, and New
England forests would not be scientifically sound. The agencies instead
have chosen to establish a more flexible approach to implementing this
rule that accounts for specific conditions in each region. Moreover, it
would often be infeasible for the regulated community or agency staff
to determine whether a stream ordinarily flows or whether a lake
contains standing water, for example, 12 weeks as opposed to 11 weeks
per year. Even if this determination was possible, such a bright line
cutoff would not reflect

hydrological diversity among different regions and alterations in flow
characteristics. The agencies' conclusion that a minimum duration is
not feasible is consistent with the pre-2015 regulatory regime, which
did not establish a bright line cutoff (though provided three months as
an example of seasonal flow) and with the approach of the 2020 NWPR.
See 85 FR 22292 (April 21, 2020) (``The agencies are not providing a
specific duration (e.g., the number of days, weeks, or months) of
surface flow that constitutes intermittent flow, as the time period
that encompasses intermittent flow can vary widely across the country
based upon climate, hydrology, topography, soils, and other
conditions.'').
    Many factors, including climate, hydrology, topography, soils, and
other conditions, may affect the period in which relatively permanent
flow may occur for those relatively permanent waters that do not have
continuously flowing or standing water year-round. The factors which
affect streamflow and flow cessation are climatically and
geographically specific and therefore the periods during which a
tributary might have relatively permanent flow vary by region. Non-
relatively permanent tributaries are similarly diverse, and the
mechanisms which differentiate relatively permanent flow from non-
relatively permanent flow also vary by region.
    For example, in parts of the Southeastern United States,
precipitation is distributed somewhat uniformly throughout the year,
but increased evapotranspiration during the growing season can reduce
surficial ground water levels and reduce or remove surface flows late
in the growing season (e.g., late summer or early autumn).
Consequently, certain streams in the Southeast may flow primarily in
the winter or early spring. Non-relatively permanent tributaries in the
Southeast may often be characterized by the repeated sequence of
streamflow, flow cessation, and channel drying throughout the year,
where the onset of streamflow coincides with distinct rainfall events
and is driven primarily by storm runoff. Streamflow in these systems
may persist anywhere from a few hours to days at a time, where the
cessation of flow is most often associated with termination of overland
flow, hillslope runoff recession, and the depletion of water in
saturated soils. Although streamflow in these tributaries may occur
regularly, off and on, over the duration of a season or longer, they do
not exhibit continuously flowing water for an extended period at any
point during the year. In other areas of the United States, snowpack
melt drives streamflow more than rainfall, and relatively permanent
flow may therefore coincide with warming temperatures in the spring or
early summer.
    Many headwater streams in mountainous regions flow through channels
incised in bedrock with no groundwater interface with the bed of the
stream. Instead, these streams are often fed primarily by high
elevation snowpack melt. The same scenario may also exist in Northern
regions, where flows could be fed almost exclusively through melting
snowpack absent elevated groundwater tables. In these regions,
relatively permanent flows coincide with warming temperatures in the
spring or early summer and may persist well into the summer until there
are no longer enough inputs to sustain surface water, or later into
autumn when more permanent sources of meltwater (e.g., glaciers or
snowfields) begin to freeze. Non-relatively permanent flows in these
regions may occur in basins with thin layers of snow, where snow melts
rapidly at the onset of spring thaw, and the snowmelt produced is not
sufficient to sustain flows for an extended period and into the summer.
    To determine the flow characteristics of a tributary for purposes
of implementing this rule, the agencies will evaluate the entire reach
of the tributary that is of the same Strahler \101\ stream order (i.e.,
from the point of confluence, where two lower order streams meet to
form the tributary, downstream to the point such tributary enters a
higher order stream; see Technical Support Document section IV.A.ii.1).
The flow characteristics of lakes, ponds, and impoundments that are
part of the tributary network will be assessed in conjunction with the
stream they connect to. Consistent with the pre-2015 regulatory regime,
the agencies will assess the flow characteristics of a particular
tributary at the farthest downstream limit of such tributary (i.e., the
point the tributary enters a higher order stream). Rapanos Guidance at
6 n.24. Where data indicate the flow characteristics at the downstream
limit are not representative of the entire reach of the tributary, the
flow characteristics that best characterize the entire tributary reach
will be used.
---------------------------------------------------------------------------

    \101\ Strahler, A.N. 1957. ``Quantitative analysis of watershed
geomorphology.'' American Geophysical Union Transactions 38: 913-
920.
---------------------------------------------------------------------------

(2) Source of Flow for Relatively Permanent Tributaries
    Implementation of the relatively permanent standard for tributaries
in this rule does not require that relatively permanent flow come from
particular sources. This rule's approach is consistent with the
plurality opinion in Rapanos, which lays out the relatively permanent
standard and does not require that relatively permanent waters
originate from any particular source. See, e.g., 547 U.S. at 739. This
rule's approach is also science-based, as the source of a tributary's
flow does not influence its effect on downstream waters, including
paragraph (a)(1) waters. This rule's approach is similar to the
familiar approach taken in the Rapanos Guidance and the 2020 NWPR,
which also did not specify that relatively permanent flow come from
particular sources.
    Sources of flow in relatively permanent tributaries may include an
elevated groundwater table that provides baseflow to a channel bed.
Relatively permanent flow could also result from upstream contributions
of flow, effluent flow, or snowpack that melts slowly over time in
certain geographic regions or at high elevations. In addition, in
certain regions relatively permanent flow could result from a
concentrated period of back-to-back precipitation events that leads to
sustained flow through a combination of runoff and upstream
contributions of flow or an elevated groundwater table that provides
baseflow to the channel bed. In contrast, non-relatively permanent
tributaries may flow only during or shortly after individual
precipitation events (including rainfall or snowfall events). Non-
relatively permanent flow may occur simply because it is raining or has
very recently rained, or because a recent snow has melted.
    Streamflow that occurs during the monsoon season in certain parts
of the country (typically June through September in the arid West) may
be relatively permanent or non-relatively permanent, depending on the
conditions at the location. Many tributaries in the arid West are
dominated by coarse, alluvial sediments and exhibit high transmission
losses, resulting in streams that often dry rapidly following a storm
event (e.g., within minutes, hours, or days). These streams are not
relatively permanent under this rule. However, relatively permanent
flow may occur as a result of multiple back-to-back storm events
throughout a watershed, during which the combination of runoff and
upstream contributions of flow is high enough to exceed rates of
transmission loss for an extended period of time. Relatively permanent
flow may also follow one or more larger storm events, when

floodwaters locally recharge the riparian aquifer through bank
infiltration, which supplies sustained baseflow throughout the monsoon
season.
    Similar to the 2020 NWPR's approach, the agencies will consider
tributaries that flow in direct response to ``snowfall'' for only a
short duration during or shortly after that snowfall event to be non-
relatively permanent waters under this rule. Streams that flow as a
result of ``snowpack melt'' will be considered relatively permanent
waters under this rule, where snowpack is defined as ``layers of snow
that accumulate over extended periods of time in certain geographic
regions or at high elevation (e.g., in northern climes or mountainous
regions).'' See 85 FR 22275 (April 21, 2020). Tributaries that receive
effluent flow that is relatively permanent will also be assessed under
the relatively permanent standard.
(3) Tools Available To Determine Whether a Tributary Meets the
Relatively Permanent Standard
    Section IV.C.4.c.i of this preamble discusses how to determine if
features on the landscape are tributaries. Direct observations and
various remote tools and resources can be used to identify tributary
reaches based on stream order, and topographic characteristics can
assist in determining stream order. USGS topographic map blue line
symbology and contour line patterns can be used to interpret the
connectivity and contribution of flow within a river network, as well
as topography within an evaluation area. Elevation models, including
those based on light detection and ranging (LIDAR) derived data, may
also illustrate tributary connectivity and flow patterns, as well as
topography. In addition, aerial and satellite imagery along with maps
or geospatial mapping products (e.g., NHD, NWI, soil maps, and Tribal,
State, or local maps) can be used to help identify tributary reaches
based on stream order. In addition to remote tools and resources,
factors identified through field observations can be used to help
determine the extent of a tributary reach. For example, tributary
systems can be traversed to identify and characterize the branches of
the network that contribute flow to a particular evaluation area.
Certain geographic features (e.g., non-jurisdictional ditches, swales)
may also be found to contribute to a tributary's surface hydrology.
    Many available resources and tools can assist in determining
whether tributaries are relatively permanent. For instance, the
agencies have been working to develop regionalized streamflow duration
assessment methods (SDAMs, available at https://www.epa.gov/streamflow-duration-assessment), which are rapid field-based assessment methods
that can be used to classify streamflow duration and assist in
determining whether tributaries are ``relatively permanent.'' These
methods rely on physical and/or biological field indicators, such as
the presence of hydrophytic vegetation and benthic macroinvertebrates,
that can be collected or observed in a single site visit to determine
the flow duration of a tributary in a reliable and rapid way. EPA, the
Corps, and the State of Oregon developed a regionalized SDAM that has
been validated for use throughout the Pacific Northwest (available at
http://www.epa.gov/measurements/streamflow-duration-assessment-method-pacific-northwest). EPA and the Corps have also developed a beta SDAM
for the arid West (available at https://www.epa.gov/streamflow-duration-assessment/beta-streamflow-duration-assessment-method-arid-west) and the Western Mountains (available at https://www.epa.gov/streamflow-duration-assessment/beta-streamflow-duration-assessment-method-western-mountains). EPA and the Corps are working to develop
additional regionalized SDAMs in other parts of the country. Other
agencies have developed similar tools that may be useful in
implementing this rule.\102\ The agencies, co-regulators, and
stakeholders can use the regionalized field indicators from SDAMs to
quickly and easily identify tributaries that are relatively permanent
as interpreted by the agencies under this rule.
---------------------------------------------------------------------------

    \102\ E.g., the Streamflow Methodology for Identification of
Intermittent and Perennial Streams and Their Origins, developed by
the North Carolina Division of Water Quality, available at https://files.nc.gov/ncdeq/Water%20Quality/Surface%20Water%20Protection/401/Policies_Guides_Manuals/StreamID_v_4point11_Final_sept_01_2010.pdf.
---------------------------------------------------------------------------

    Remote or desktop tools can also help the agencies and the public
better understand streamflow and whether tributaries have continuously
flowing or standing water year-round or during certain times of the
year for more than for a short duration in direct response to
precipitation.\103\ Satellite imagery and aerial photographs showing
visible water on multiple dates can provide evidence as to whether
tributaries have relatively permanent flow. Aerial photographs may show
other indicators commonly used to identify the presence of an
OHWM.\104\ These indicators may include the destruction of terrestrial
vegetation, the absence of vegetation in a channel, and stream channel
morphology with evidence of scour, material sorting, and deposition.
These indicators from aerial photographs can be correlated to the
presence of USGS stream data to support an assessment of flow
characteristics for a tributary.
---------------------------------------------------------------------------

    \103\ These tools include local maps, StreamStats by the USGS
(available at https://streamstats.usgs.gov/ss/), Probability of
Streamflow Permanence (PROSPER) by the USGS, which provides
streamflow permanence probabilities during the summer for stream
reaches in the Pacific Northwest (available at https://www.usgs.gov/centers/wyoming-montana-water-science-center/science/probability-streamflow-permanence-prosper), and NRCS hydrologic tools and soil
maps. Other tools include regional desktop tools that provide for
the hydrologic estimation of a discharge sufficient to generate
intermittent or perennial flow (e.g., a regional regression analysis
or hydrologic modeling), or modeling tools using drainage area,
precipitation data, climate, topography, land use, vegetation cover,
geology, and/or other publicly available information. Some models
that are developed for use at the reach scale may be localized in
their geographic scope. NOAA national snow analyses maps can
facilitate the evaluation of seasonal flow from snowmelt (available
at https://www.nohrsc.noaa.gov/nsa/), as can NRCS sources (available
at https://www.wcc.nrcs.usda.gov/snow/), and hydrographs that may
indicate a large increase in stream discharge due to the late
spring/early summer thaws of melting snow.
    \104\ See definition of OHWM in section IV.C.8.d of this
preamble and https://www.erdc.usace.army.mil/Media/Fact-Sheets/Fact-Sheet-Article-View/Article/486085/ordinary-high-water-mark-ohwm-research-development-and-training/.
---------------------------------------------------------------------------

    In addition to satellite imagery and aerial photographs, desktop
tools, such as a regional regression analysis and the Hydrologic
Modeling System (HEC-HMS), provide for the hydrologic estimation of
stream discharge in tributaries under regional conditions. The
increasing availability of LIDAR-derived data can also be used to help
implement this rule.\105\ Potential LIDAR-indicated tributaries can be
correlated with aerial photography or high-resolution satellite imagery
interpretation and USGS stream gage data, to reasonably conclude the
presence of an OHWM and shed light on the flow characteristics.
---------------------------------------------------------------------------

    \105\ Where LIDAR data have been processed to create elevation
data such as a bare earth model, detailed depictions of the land
surface are available and subtle elevation changes can indicate a
tributary's bed and banks and channel morphology. Visible linear and
curvilinear incisions on a bare earth model can help identify the
flow characteristics of a water in greater detail than aerial
photography interpretation alone. Several tools (e.g., TauDEM,
Whitebox, GeoNet) can assist in developing potential stream networks
based on contributing areas, curvature, and flowpaths using GIS.
---------------------------------------------------------------------------

    Regional field observations can be used to verify desktop
assessments of the relative permanence of a tributary, when necessary.
Geomorphic indicators could include active/relict floodplains,
substrate sorting, clearly defined and continuous bed and banks,
depositional bars and benches, and recent alluvial deposits. Hydrologic
indicators might

include wrack/drift deposits, hydric soils, or water-stained leaves.
Biologic indicators could include aquatic mollusks, crayfish, benthic
macroinvertebrates, algae, and wetland or submerged aquatic plants. As
noted above, the agencies are developing SDAMs for use throughout the
country which evaluate and interpret these indicators and can show
whether tributaries have continuously flowing or standing water year-
round or during certain times of the year for more than a short
duration in direct response to precipitation. Ultimately, multiple
indicators, data points, and sources of information may be used to
determine whether a water, including a tributary, is relatively
permanent.
iii. Determining Whether a Tributary Meets the Significant Nexus
Standard
    In evaluating tributaries under the significant nexus standard, the
agencies will determine whether the tributaries, either alone or in
combination with similarly situated waters in the region, significantly
affect the chemical, physical, or biological integrity of paragraph
(a)(1) waters. See section IV.C.9 of this preamble for additional
discussion on the definition of ``significantly affect'' in this rule,
including the factors that will be evaluated and the functions that
will be assessed as part of a significant nexus analysis. The agencies
consider tributaries and their adjacent wetlands to be ``similarly
situated'' waters. The agencies consider similarly situated waters to
be ``in the region'' when they lie within the catchment area of the
tributary of interest. Identifying the catchment area for purposes of
this significant nexus analysis is described below. The agencies
developed this updated evaluation method from the current pre-2015
implementation approach informed by their experience, the best
available science, Supreme Court decisions, and public comments.
Accordingly, in implementing the significant nexus standard under this
rule, all tributaries and adjacent wetlands within the catchment area
of the tributary of interest will be analyzed as part of the
significant nexus analysis.\106\
---------------------------------------------------------------------------

    \106\ This implementation approach to the region for purposes of
the significant nexus standard is a change from the Rapanos
Guidance. See section IV.C.9.c of this preamble for additional
discussion on implementing the significant nexus analysis.
---------------------------------------------------------------------------

    For purposes of a significant nexus analysis, the agencies will
identify the ``region'' as the catchment that drains to and includes
the tributary of interest. A catchment is the area of the land surface
that drains to a specific location for a specific hydrologic feature.
Catchments will be delineated from the downstream-most point of the
tributary reach of interest and include the land uphill that drains to
that point. For example, if the tributary of interest is a second order
stream, the catchment would be delineated from the point that the
second order stream enters a third order stream. See discussion of
stream order in section IV.C.4.c.ii.1 of this preamble. Topography and
landscape position influence the size and configuration of a catchment.
    There are many existing spatial analysis tools that can be used to
delineate catchments quickly and reliably in most parts of the country.
USGS topographic maps can be manually interpreted to delineate
catchments based on the location of the outlet point (the downstream-
most point of the tributary of interest where the tributary enters a
higher order stream), using calculations informed by topographic
contours, the alignment of topographic high spots, and grouping of
lower, valley bottoms. Various GIS tools, web applications, and
automated modeling systems can also delineate catchments based on one
or more of the many factors that can influence drainage, including
surface topography, climate, land use, the presence of hydrologic
sinks, topology of sewer systems, and design of wastewater treatment
plant service areas.\107\
---------------------------------------------------------------------------

    \107\ NHDPlus provides delineated catchments for individual
stream segments by linking the mapped stream network to the
landscape. In addition, StreamStats by the USGS (available at
https://streamstats.usgs.gov/ss/) is a map-based web tool that can
delineate drainage areas for streams and estimate flow
characteristics for selected sites based on stream gage data, basin
characteristics, climate, etc. EPA's EnviroAtlas Interactive Map
(available at https://www.epa.gov/enviroatlas/enviroatlas-interactive-map) has a wide variety of tools that can help delineate
catchments, including a tool that illustrates how precipitation will
flow over the land surface, mapped elevation profiles for selected
tributaries, and designations of upstream and downstream watersheds
within a stream network.
---------------------------------------------------------------------------

    After identifying the catchment, the next step is to identify the
tributaries within the catchment under the agencies' longstanding
interpretation of tributary, see section IV.C.4.a of this preamble
above, and any of their adjacent wetlands within the catchment area.
See section IV.C.5 of this preamble for additional discussion on how to
identify adjacent wetlands. The agencies' longstanding practice in
conducting the significant nexus analysis is to assess a tributary in
combination with wetlands that meet the definition of ``adjacent''
under the regulations. Rapanos Guidance at 10. This approach to the
significant nexus analysis recognizes the ecological relationship
between the tributaries and their adjacent wetlands, and the role those
similarly situated waters have in influencing the chemical, physical,
or biological integrity of paragraph (a)(1) waters. See section
III.E.iii of the Technical Support Document. For purposes of this rule,
the agencies will therefore assess the tributaries and their adjacent
wetlands in a catchment. If the tributaries in the region, including
the tributary under assessment, have no adjacent wetlands, the agencies
consider only the factors and functions of the tributaries in
determining whether there is a significant effect on the chemical,
physical, or biological integrity of downstream paragraph (a)(1)
waters. If any of the tributaries in the region, including the
tributary under assessment, have adjacent wetlands, the agencies will
consider the factors and functions of the tributaries, including the
tributary under assessment, together with the functions performed by
the wetlands adjacent to the tributaries in the catchment, in
evaluating whether a significant nexus is present.
    In conducting a significant nexus analysis under this rule, the
agencies will evaluate available hydrologic information (e.g., gage
data, precipitation records, flood predictions, historic records of
water flow, statistical data, personal observations/records, etc.) and
physical indicators of flow including the presence and characteristics
of a reliable OHWM. To understand the chemical, physical, and
biological functions provided by tributaries and their adjacent
wetlands, and the effects those functions have on paragraph (a)(1)
waters, it is important to use relevant geographic water quality data
in conjunction with site-specific data from field sampling and
hydrologic modeling. See section IV.C.9.c of this preamble for
additional discussion on implementing the significant nexus analysis;
see also section IV.C.10 of this preamble.
5. Adjacent Wetlands
a. This Rule
    Consistent with the proposal, this rule retains the adjacent
wetlands provision of the 1986 regulations, with amendments to reflect
the agencies' interpretation of the statutory limits on the scope of
the ``waters of the United States'' informed by the law, the science,
and agency expertise. Aquatic resources that meet this rule's
definitions of ``wetlands'' and ``adjacent'' are assessed under this
provision where they are adjacent to traditional navigable waters, the
territorial seas, interstate waters,

impoundments of jurisdictional waters, and tributaries.
    As discussed further in section IV.C.8.a of this preamble, in this
rule the agencies are retaining their longstanding definition of
``wetlands'' from the 1986 regulations: ``Wetlands means those areas
that are inundated or saturated by surface or ground water at a
frequency and duration sufficient to support, and that under normal
circumstances do support, a prevalence of vegetation typically adapted
for life in saturated soil conditions. Wetlands generally include
swamps, marshes, bogs, and similar areas.''
    Additionally, as discussed further in section IV.C.8.b of this
preamble, in this rule the agencies are retaining their longstanding
definition of ``adjacent'' unchanged for most of the past 45 years,
which provides: ``Adjacent means bordering, contiguous, or neighboring.
Wetlands separated from other waters of the United States by man-made
dikes or barriers, natural river berms, beach dunes, and the like are
`adjacent wetlands.' '' Under this definition, adjacency is focused on
the distance between the wetland and the jurisdictional water. Whether
the distance between the wetland and the jurisdictional water qualifies
the wetland as bordering, contiguous, or neighboring (and therefore
``adjacent'') depends on the factual circumstances. The agencies have
three well-established criteria to determine adjacency; if any one of
the criteria is met, the wetland is ``adjacent,'' but may require
further analysis to determine if it is ``waters of the United States.''
See Rapanos Guidance at 5-8. First, there is an unbroken surface or
shallow subsurface connection to a jurisdictional water, which can be
established, for example, where the wetland directly abuts the
jurisdictional water or by a non-jurisdictional physical feature that
provides the direct connection between the wetland and a jurisdictional
water, such as a pipe, culvert, non-jurisdictional ditch, or flood
gate, that has at least periodic flow. Second, the wetland is
physically separated from a jurisdictional water by human-made dikes or
barriers, or natural landforms (e.g., river berms, beach dunes). Or
third, the wetland's proximity to a jurisdictional water is reasonably
close such that ``adjacent wetlands have significant effects on water
quality and the aquatic ecosystem.'' Riverside Bayview, 474 U.S. at 135
n.9. The agencies conclude that close proximity between an adjacent
wetland and a jurisdictional water means the wetland can modulate water
quantity or water quality in the jurisdictional water, and the
jurisdictional water can modulate water quantity or quality in the
wetland. See section IV.C.5.c of this preamble for further discussion
on the implementation of this provision and the three criteria. The
agencies have not established a specific distance limitation in the
rule beyond which wetlands are never adjacent because whether a wetland
is reasonably close such that the wetland can modulate water quantity
or quality in the jurisdictional water or the jurisdictional water can
modulate water quantity or quality in the wetland as part of the same
aquatic ecosystem, depends on regional variations in climate,
landscape, and geomorphology. But the agencies can state based on
nearly 45 years of implementation of this definition that in a
substantial number of cases, adjacent wetlands abut (touch) a
jurisdictional water. And, on the whole, nationwide, adjacent wetlands
are within a few hundred feet from jurisdictional waters (and in the
instances where the distance is greater than a few hundred feet,
adjacency is likely supported by a pipe, non-jurisdictional ditch,
karst geology, or some other feature that connects the wetland directly
to the jurisdictional water). Because of regional variability and its
effects on proximity for purposes of adjacency, wetlands in the arid
West--where rainfall is generally lower, evaporation rates are higher,
and riparian areas and floodplains do not extend far from the tributary
network--are likely to be much closer than a few hundred feet to be
considered adjacent under this rule. On the other hand, where the
jurisdictional water is wide, topography is flat lending to larger
floodplains and riparian areas, and rainfall is higher, wetlands are
more likely to be determined to be reasonably close where they are a
few hundred feet from that tributary because the site-specific
conditions contribute to the close relationship between the wetland and
the jurisdictional water, including any unbroken surface or shallow
subsurface hydrologic connections between the waters.
    While bright-line rules (for example, wetlands that are more than a
specific number of feet from a jurisdictional water are not
``adjacent'') are easiest to understand and implement, convenience is
not the only goal the agencies must consider in administering the Clean
Water Act. Because the relationship between a wetland and a proximate
jurisdictional water can depend upon a number of site-specific factors,
like climate, geomorphology, landscapes, hydrology, and size of the
jurisdictional water (e.g., the ocean compared to a headwater stream),
and because the central purpose of the Act is to protect the integrity
of the nation's waters, a more nuanced analysis is required. While
science says that all things being equal, distance, location in a
riparian area or floodplain, or discrete hydrologic connections are
more likely to strengthen the relationship between a wetland and a
nearby water, science does not provide bright lines on appropriate
distances to determine adjacency. In implementing this provision over
the years, the agencies have worked hard to balance the desire for
clarity and predictability with the agencies' scientific understanding
of the resources Congress has charged the agencies with protecting. The
agencies have carefully considered options for nationally applicable
bright lines with respect to adjacency, such as establishing that any
wetland within a certain number of feet from a jurisdictional tributary
is per se jurisdictional, in order to facilitate implementation of the
Clean Water Act and to minimize the burden on both landowners and the
agencies to evaluate the scope of ``waters of the United States.''
However, the United States is a vast country with many different types
of waters, watersheds, landscapes, and hydrology. In fact, in the 2015
Clean Water Rule the agencies sought to establish a distance-based
bright line for determining adjacency. As discussed in section IV.B.1
of this preamble, that rule was immediately challenged, and the
distance-based limitations were a substantial factor in many of the
challenges. As the Supreme Court itself has recognized, the scope of
Clean Water Act jurisdiction does not easily lend itself to bright
lines: ``In sum, we recognize that a more absolute position . . . may
be easier to administer. But, as we have said, those positions have
consequences that are inconsistent with major congressional objectives,
as revealed by the statute's language, structure, and purposes.'' Maui,
140 S. Ct. at 1477. Ultimately, for purposes of this rule, the agencies
concluded that there was not a reasoned basis, consistent with the text
of the statute, to establish such a regulatory bright line.
    The adjacent wetlands provision in the 1986 regulations defined
``waters of the United States'' to include wetlands adjacent to
traditional navigable waters, interstate waters, paragraph (a)(3)
``other waters,'' impoundments of ``waters of the United States,''
tributaries, and the territorial seas. This rule provides additional
constraints on jurisdiction relative to the 1986 regulatory text by

defining ``waters of the United States'' to include: (1) wetlands
adjacent to traditional navigable waters, the territorial seas, and
interstate waters; (2) wetlands adjacent to and with a continuous
surface connection to relatively permanent paragraph (a)(2)
impoundments or jurisdictional tributaries when the jurisdictional
tributaries meet the relatively permanent standard; and (3) wetlands
adjacent to paragraph (a)(2) impoundments or jurisdictional tributaries
when the wetlands meet the significant nexus standard. In other words,
for wetlands adjacent to waters that are not paragraph (a)(1) waters,
an additional showing of a continuous surface connection to a
relatively permanent water or of a significant nexus to a paragraph
(a)(1) water is required. The determination of whether a wetland is
``adjacent'' is distinct from whether an ``adjacent'' wetland meets the
relatively permanent standard; however, wetlands that have a continuous
surface connection to a relatively permanent water meet the definition
of ``adjacent'' and thus are a subset of adjacent wetlands. See section
IV.C.5.c of this preamble for further information related to
implementing the final rule's adjacent wetlands provision.
    Under this rule, the relatively permanent standard and the
significant nexus standard are independent jurisdictional standards.
Under the relatively permanent standard for adjacent wetlands, wetlands
meet the continuous surface connection requirement if they physically
abut, or touch, a relatively permanent paragraph (a)(2) impoundment or
a jurisdictional tributary when the jurisdictional tributary meets the
relatively permanent standard, or if the wetlands are connected to
these waters by a discrete feature like a non-jurisdictional ditch,
swale, pipe, or culvert. A natural berm, bank, dune, or similar natural
landform between an adjacent wetland and a relatively permanent water
does not sever a continuous surface connection to the extent it
provides evidence of a continuous surface connection. Again, the
determination of whether a wetland is ``adjacent'' under the rule is
distinct from whether an ``adjacent'' wetland has a continuous surface
connection. See section IV.C.5.c of this preamble, below, for further
discussion of implementation of the final rule's adjacent wetlands
provision.
    The agencies have amended the regulatory text from the proposed
rule to be clearer that a wetland adjacent to but lacking a continuous
surface connection to a tributary that is relatively permanent must be
assessed under the significant nexus standard. For example, if a
wetland is ``neighboring'' to a tributary that is relatively permanent,
and thus ``adjacent,'' but lacks a continuous surface connection to
that tributary, the wetland would need to be assessed under the
significant nexus standard in order to determine its jurisdictional
status. This is consistent with pre-2015 practice under the Rapanos
Guidance for wetlands adjacent to relatively permanent tributaries and
was the agencies' intent under the proposed rule language. See Rapanos
Guidance at 8; 86 FR 69423 (``Wetlands adjacent to relatively permanent
tributaries but that lack a continuous surface connection to such
waters would then be assessed under the significant nexus [standard],
along with the tributary.'').
    In addition, under this rule, wetlands adjacent only to paragraph
(a)(5) waters cannot be considered for jurisdiction under the paragraph
(a)(4) adjacent wetlands category, which represents a change from the
1986 regulations. Instead, such wetlands could be considered for
jurisdiction solely under paragraph (a)(5) of this rule.
    Further, in this rule, the agencies are deleting the parenthetical
from the 1986 regulations that limited the scope of jurisdictional
adjacent wetlands to wetlands adjacent to waters ``(other than waters
that are themselves wetlands)'' for the reasons discussed below.
b. Summary of the Agencies' Consideration of Public Comments and
Rationale for This Rule
    The agencies received numerous comments on the scope and
implementation of the adjacent wetlands provision.
i. Comments on the Adjacent Wetlands Provision
    The agencies received a wide range of comments on adjacent
wetlands. Some commenters stated that they agreed with the agencies'
approach in the proposed rule for adjacent wetlands, with several
adding that they believed the proposed rule's approach to adjacency was
consistent with prior practice, the relevant case law, the statute, the
Constitution, or congressional intent. Other commenters disagreed and
stated that the agencies' approach was not consistent with case law,
the statute, the Constitution, or congressional intent. Many of those
commenters stated that wetlands should only be jurisdictional if they
meet the relatively permanent standard. Other commenters requested
greater jurisdictional protections for wetlands due to the many
functions that they provide that benefit downstream waters, with some
commenters requesting that adjacent wetlands be treated as
categorically jurisdictional, similar to the 2015 Clean Water Rule.
    After careful consideration of public comments and for the reasons
described in this preamble, the agencies are promulgating the adjacent
wetlands provision of this rule with minimal changes to the proposed
rule. For wetlands adjacent to paragraph (a)(1) waters, adjacency alone
supports jurisdiction. For wetlands that are adjacent to waters that
are not paragraph (a)(1) waters, like tributaries, this rule
establishes an additional limitation on jurisdiction. In that case, the
adjacent wetlands are jurisdictional only if they meet either the
relatively permanent standard or the significant nexus standard. The
agencies agree with commenters who stated that the proposed rule's
approach to adjacent wetlands was generally consistent with prior
practice and consistent with the relevant case law, the statute, the
Constitution, and congressional intent, and thus disagree with
commenters who took the contrary view. This rule defines ``waters of
the United States'' to include adjacent wetlands and reflects the
agencies' interpretation of the statutory limits on the scope of the
``waters of the United States'' informed by the text of the relevant
provisions of the Clean Water Act and the statute as a whole, relevant
Supreme Court decisions, the scientific record, the agencies'
experience and technical expertise, and consideration of public
comments on the proposed rule. The agencies disagree with commenters
who stated that only adjacent wetlands that meet the relatively
permanent standard should be considered jurisdictional. As discussed
further in section IV.A.3.a.ii of this preamble, the agencies have
concluded that the relatively permanent standard is administratively
useful but is insufficient as the sole standard for geographic
jurisdiction under the Clean Water Act because it is inconsistent with
the Act's text and objective. Protecting only waters that meet the
relatively permanent standard also runs counter to the scientific
principles underlying protection of water quality. The agencies thus
are promulgating an approach to adjacent wetlands that includes, but
that is not limited to, the relatively permanent standard. The
ecological relationship between jurisdictional waters and their
adjacent wetlands is well documented in the scientific literature and
reflects their physical proximity as well as shared hydrological and
biological characteristics. The scientific literature

also supports the conclusion that adjacent wetlands, either alone or in
combination with similarly situated waters, provide many important
functions that can significantly affect the chemical, physical, and
biological integrity of paragraph (a)(1) waters. See Technical Support
Document section III.B. Section IV.A of this preamble provides
additional information about the legal basis for the agencies'
conclusions in this rule and the scientific support for the rule's
provisions regarding adjacent wetlands. The agencies are not making
additional categorical determinations of jurisdiction based on the
significant nexus standard, as described further in section IV.A of
this preamble. Even under the 2020 NWPR, which purported to enhance
clarity, a landowner could not tell simply by looking at their property
whether it contained ``waters of the United States'' because, in the
case of adjacent wetlands, it was necessary to determine (1) whether
the property contained a wetland as defined in the regulations, (2)
whether there was evidence of a continuous surface connection between
the wetland and a water that was part of the tributary network of a
traditional navigable water or the territorial seas, (3) whether there
was evidence that the continuous surface connection occurred in a
``typical year,'' as the rule defined that term, and (4) in the case of
a continuous surface connection based on inundation, whether the
inundation originated in the jurisdictional water (relevant to
adjacency under that rule) or the wetland (irrelevant to adjacency
under that rule).
    The challenge inherent in establishing bright lines to address the
complex and variable ways in which waters move in different regions
across the country is longstanding. As the Supreme Court itself has
recognized, the scope of Clean Water Act jurisdiction does not easily
lend itself to bright lines: ``In sum, we recognize that a more
absolute position . . . may be easier to administer. But, as we have
said, those positions have consequences that are inconsistent with
major congressional objectives, as revealed by the statute's language,
structure, and purposes.'' Maui, 140 S. Ct. at 1477. Further, as early
Supreme Court decisions recognized, the Clean Water Act replaced a
system whereby water quality protection had to be resolved through
litigation in which courts had to apply ``often vague and indeterminate
nuisance concepts and maxims of equity jurisprudence.'' City of
Milwaukee, 451 U.S. at 317. The Clean Water Act replaced this
unpredictable and inefficient approach with ``a comprehensive
regulatory program supervised by an expert administrative agency,''
id., including a ``uniform system of interstate water pollution
regulation,'' Arkansas v. Oklahoma, 503 U.S. 91, 110 (1992). Shrinking
Federal jurisdiction, as the 2020 NWPR did, for example, would place
many waters back within the ``vague and indeterminate'' legal regime
that the Supreme Court recognized the Clean Water Act was designed to
replace. See 451 U.S. at 317.
    The agencies also received a variety of comments critiquing or
supporting various past practice and rulemaking approaches to adjacency
including the pre-2015 regulatory regime, the 2015 Clean Water Rule,
and the 2020 NWPR. The agencies are retaining their longstanding
definition of adjacency and establishing an approach to adjacency that
is generally consistent with the pre-2015 regulatory regime, with some
changes to implementation discussed below. The agencies are rejecting
certain aspects of the 2020 NWPR's approach to adjacent wetlands for
the reasons discussed in this section and section IV.B.3 of this
preamble. The definition of ``adjacent wetlands'' in the 2020 NWPR
failed to advance the objective of the Clean Water Act. It also was
inconsistent with scientific information about the important effects of
wetlands that do not abut jurisdictional waters and that lack evidence
of specific surface water connections to such waters on the integrity
of paragraph (a)(1) waters. In addition, key elements of the 2020
NWPR's definition of ``adjacent wetlands'' were extremely difficult to
implement. These deficiencies are reflected in substantial losses of
Federal protections on the ground. See section IV.B.3 of this preamble.
The agencies are maintaining the approach of the pre-2015 regulatory
regime and the 2015 Clean Water Rule under which wetlands adjacent to
traditional navigable waters, the territorial seas, and interstate
waters are jurisdictional without need for further determinations, but
the agencies are not determining that any additional adjacent wetlands
are categorically jurisdictional in this rule. The agencies have
authority to determine which tributaries and their adjacent wetlands
are jurisdictional either through regulations or adjudication. See
Rapanos, 547 U.S. at 780-81 (Kennedy, J., concurring in the judgment);
see also NLRB v. Bell Aerospace Co., 416 U.S. 267, 294 (1974). With
respect to wetlands adjacent to waters other than paragraph (a)(1)
waters, the agencies have decided to proceed through case-specific
jurisdictional determinations under this rule, rather than through
categorical determinations by rule.
    The agencies will continue to assert jurisdiction over wetlands
adjacent to traditional navigable waters, the territorial seas, and
interstate waters without need for further assessment, as they did
under the 1986 regulations and the Rapanos Guidance. Indeed, in
Rapanos, at least five Justices agreed that wetlands adjacent to
traditional navigable waters are ``waters of the United States.'' See
Rapanos, 547 U.S. at 780 (Kennedy, J., concurring in the judgment)
(``As applied to wetlands adjacent to navigable-in-fact waters, the
Corps' conclusive standard for jurisdiction rests upon a reasonable
inference of ecologic interconnection, and the assertion of
jurisdiction for those wetlands is sustainable under the Act by showing
adjacency alone.''), id. at 810 (Stevens, J., dissenting) (``Given that
all four Justices who have joined this opinion would uphold the Corps'
jurisdiction in both of these cases--and in all other cases in which
either the plurality's or Justice Kennedy's test is satisfied--on
remand each of the judgments should be reinstated if either of those
tests is met.''); see also Riverside Bayview, 474 U.S. at 134 (``[T]he
Corps' ecological judgment about the relationship between waters and
their adjacent wetlands provides an adequate basis for a legal judgment
that adjacent wetlands may be defined as waters under the Act.'');
Rapanos Guidance at 5. Moreover, ample scientific information makes
clear that the health and productivity of rivers and lakes, including
paragraph (a)(1) waters, depends upon the functions provided by
upstream tributaries, adjacent wetlands, and paragraph (a)(5) waters.
Under this rule, the agencies also define ``waters of the United
States'' to include wetlands adjacent to the territorial seas without
need for further assessment, as they did under the 1986 regulations, as
the territorial seas are categorically protected under the Clean Water
Act. Additionally, under this rule the agencies continue to define
``waters of the United States'' to include wetlands adjacent to
interstate waters without need for further assessment since interstate
waters, like traditional navigable waters and the territorial seas, are
waters clearly protected by the Clean Water Act. See section IV.C.2 of
this preamble for further discussion of traditional navigable waters,
the territorial seas, and interstate waters.
    The agencies are retaining the 1986 regulations' coverage of
wetlands adjacent to paragraph (a)(2)

impoundments and wetlands adjacent to tributaries to paragraph (a)(2)
impoundments, updated to include the requirement that the wetlands also
meet either the relatively permanent or significant nexus standard. As
discussed above in section IV.C.3 of this preamble, the agencies'
longstanding interpretation of the Clean Water Act is that ``waters of
the United States'' remain ``waters of the United States'' even if
impounded. Since the impoundment does not ``denationalize'' the
``waters of the United States,'' see S.D. Warren, 547 U.S. at 379 n.5,
the agencies similarly interpret the Clean Water Act to continue to
protect wetlands adjacent to the paragraph (a)(2) impoundment and
adjacent to jurisdictional tributaries to the impoundment where those
wetlands meet the relatively permanent standard or the significant
nexus standard. See section IV.C.3 of this preamble for additional
discussion of impoundments under this rule.
    The agencies are also deleting the cross reference to paragraph
(a)(5) waters as waters to which wetlands may be adjacent to be
determined ``waters of the United States'' under the adjacent wetlands
category of this rule. This change reflects the agencies' consideration
of the jurisdictional concerns and limitations of the statute, informed
by SWANCC and Rapanos. The agencies have concluded that a provision
that authorizes consideration of jurisdiction over adjacent wetlands
that meet the relatively permanent or significant nexus standard when
assessed based simply on connections to paragraph (a)(5) waters would
have too tenuous a connection to paragraph (a)(1) waters. Rather, any
such wetlands that are adjacent only to paragraph (a)(5) waters would
be assessed themselves under paragraph (a)(5) of this rule to determine
if they meet the relatively permanent or significant nexus standard.
For example, a wetland adjacent to a lake that meets the significant
nexus standard under paragraph (a)(5) would itself need to be assessed
under paragraph (a)(5) to determine whether it significantly affects
the chemical, physical, or biological integrity of a paragraph (a)(1)
water. See section IV.C.6.c of this preamble for further discussion on
implementation of paragraph (a)(5) waters.
    The agencies have removed the parenthetical ``(other than waters
that are themselves wetlands)'' from the regulatory text because it has
caused confusion for the public and the regulated community and is
unnecessary. The parenthetical from the 1986 regulations limited the
scope of jurisdictional adjacent wetlands to wetlands adjacent to
waters ``(other than waters that are themselves wetlands).'' Under that
provision, a wetland was not jurisdictional simply because it was
adjacent to another adjacent wetland or to a wetland jurisdictional
under paragraph (a)(3) of the 1986 regulations. The provision has
created confusion under the pre-2015 regulatory regime, as some have
asserted that a wetland that is indeed adjacent to a jurisdictional
tributary, but that is separated from that tributary by another
adjacent wetland, should not be determined to be a jurisdictional
adjacent wetland because of that parenthetical. Several commenters
discussed the parenthetical in the 1986 regulation's ``adjacent
wetlands'' category. Most of those commenters were in favor of removing
the parenthetical, claiming that it created ``confusion'' and citing
concerns that the parenthetical could improperly limit jurisdiction of
wetlands. Other commenters voiced support for keeping the
parenthetical. Some even suggested that the parenthetical flatly
excluded all wetlands that are adjacent to other wetlands, regardless
of any other considerations. These interpretations are inconsistent
with the agencies' intent and longstanding interpretation of the
parenthetical. See Universal Welding & Fabrication, Inc. v. U.S. Army
Corps of Eng'rs, 708 Fed. Appx. 301, 303 (9th Cir. 2017) (observing
that ``[d]espite the subject wetland's adjacency to another wetland,
the Corps determined that its regulatory authority was not precluded by
the parenthetical language within [section] 328.3(a)(7), which it
interpreted as prohibiting the exercise of jurisdiction over a wetland
only if based upon that wetland's adjacency to another wetland'' and
holding that the Corps' interpretation is ``the most reasonable reading
of the regulation's text''). Therefore, to streamline the regulation
and provide additional clarity, the agencies have deleted the text of
the parenthetical in this rule. In addition, wetlands adjacent to
interstate wetlands or wetlands adjacent to tidal wetlands (which are
traditional navigable waters) are jurisdictional under this rule,
consistent with the 1986 regulations and longstanding practice.
ii. Comments on the Interpretation and Implementation of the Adjacent
Wetlands Provision
    The agencies will continue to implement a number of longstanding
interpretations of ``adjacent'' based on scientific principles and
practical administration of the definition with this rule. As stated
previously, the agencies consider wetlands ``adjacent'' if one of the
following three criteria is satisfied. First, there is an unbroken
surface or shallow subsurface connection to jurisdictional waters. All
wetlands that directly abut jurisdictional waters have an unbroken
surface or shallow subsurface connection because they physically touch
the jurisdictional water. Wetlands that do not directly abut a
jurisdictional water may have an unbroken surface or shallow subsurface
connection to jurisdictional waters. Water does not need to be
continuously present in the surface or shallow subsurface connection.
Second, they are physically separated from jurisdictional waters by
human-made dikes or barriers, or natural landforms (e.g., river berms,
beach dunes). Or third, their proximity to a jurisdictional water is
reasonably close. Wetlands that meet one of these three criteria are
considered bordering, contiguous, or neighboring for purposes of this
rule.
    Several commenters provided input on these three criteria. Some
commenters stated that shallow subsurface hydrologic connections are
appropriate to consider for adjacency, while others stated that such
connections should not be considered. Several commenters stated that
there are regional differences in proximity relevant to adjacency. Some
commenters stated that wetlands should be considered adjacent even if
they are separated by human-made dikes or barriers, natural river
berms, beach dunes and the like, while other commenters did not support
that view.
    The agencies agree with commenters who stated that shallow
subsurface connections can be relevant to adjacency and will continue
to use the criteria from pre-2015 practice that an unbroken shallow
subsurface connection between a wetland and another water can
demonstrate adjacency.
    While this rule does not explicitly identify regional factors that
influence what is ``reasonably close'' for purposes of adjacency, the
agencies recognize there may be site-specific factors (e.g.,
topography) that influence what is ``reasonably close.'' This rule does
not establish specific distance limitations for adjacency, which helps
ensure that site-specific and regional factors can be considered when a
wetland is being evaluated (see section IV.C.5.c of this preamble,
below).
    The agencies agree with commenters who supported the 1986
regulation's definition of ``adjacent'' to include wetlands even if
they are separated by

natural landforms or human-made barriers for the reasons discussed in
sections IV.A.2.b.ii (explaining that the agencies' longstanding
definition of ``adjacent,'' which includes such wetlands, is a
reasonable foundation for this rule), and IV.C.8.b of this preamble,
and section III.B.ii of the Technical Support Document.
c. Implementation
    Under this provision of the rule, wetlands adjacent to traditional
navigable waters, the territorial seas, or interstate waters are
jurisdictional and do not need further analysis to determine if they
are ``waters of the United States.'' Further, wetlands adjacent to
paragraph (a)(2) impoundments and to jurisdictional tributaries are
assessed for jurisdiction under the relatively permanent standard or
significant nexus standard. Wetlands adjacent to but lacking a
continuous surface connection with tributaries that are relatively
permanent must be assessed under the significant nexus standard.
i. Determining the Presence of an Adjacent Wetland
    Before determining if a wetland is jurisdictional, the agencies
first determine if the wetland in question meets the definition of
``wetlands'' under this rule (see section IV.C.8.a of this preamble).
    In identifying wetlands, the agencies will ordinarily consider all
wetlands within a wetland mosaic collectively. The agencies have long
considered wetland mosaics to be delineated as one wetland. Wetland
mosaics are landscapes where wetland and non-wetland components are too
closely associated to be easily delineated or mapped separately, and
the wetlands in the mosaic generally act as a single ecological unit.
In certain regions where wetland mosaics are common, Corps regional
wetland delineation manuals address how to delineate such wetlands.
Longstanding practice is that wetlands in the mosaic are not
individually delineated, but that the agencies consider the entire
mosaic and estimate percent wetland in the mosaic. See Technical
Support Document section IV.A.iii. These longstanding implementation
approaches for purposes of jurisdictional determinations are supported
by the science (see Technical Support Document section IV.A.iii) and
the technical expertise the agencies have developed through years of
performing these assessments.
    Once a feature is identified as a wetland, if the wetland itself is
not jurisdictional under paragraph (a)(1) of this rule as a traditional
navigable water (such as a tidal wetland) or an interstate water, the
agencies assess whether it is adjacent to a traditional navigable
water, territorial sea, interstate water, paragraph (a)(2) impoundment,
or jurisdictional tributary. Wetlands are ``adjacent'' if they are
``bordering, contiguous, or neighboring.'' The agencies consider the
entire wetland to be ``adjacent'' if any part of the wetland is
``adjacent.''
    Under this rule's definition and consistent with the agencies'
longstanding definition, adjacency is focused on the distance between
the wetland and the jurisdictional water. Whether the distance between
the wetland and the jurisdictional water qualifies the wetland as
bordering, contiguous, or neighboring (and therefore ``adjacent'')
depends on the factual circumstances, so the agencies will assess
adjacency using the three criteria noted above in section IV.C.5.a of
this preamble. This section of the preamble explains each of the
criteria in further detail. These criteria are consistent with the text
of the regulation, the underlying scientific rationale for defining
``waters of the United States'' to include adjacent wetlands, and pre-
2015 practice. See Rapanos Guidance at 5-6.
    The longstanding definition, by its terms, does not require flow
from the wetland to the jurisdictional water or from the jurisdictional
water to the wetland (although such flow in either direction can be
relevant to the determination of adjacency). The Supreme Court in
Riverside Bayview in deferring to the Corps' ecological judgment about
the relationship between waters and their adjacent wetlands as an
``adequate basis for a legal judgment that adjacent wetlands may be
defined as waters under the Act,'' rejected an argument that such
wetlands had to be the result of flow in a particular direction to be
adjacent: ``This holds true even for wetlands that are not the result
of flooding or permeation by water having its source in adjacent bodies
of open water. The Corps has concluded that wetlands may affect the
water quality of adjacent lakes, rivers, and streams even when the
waters of those bodies do not actually inundate the wetlands. For
example, wetlands that are not flooded by adjacent waters may still
tend to drain into those waters. In such circumstances, the Corps has
concluded that wetlands may serve to filter and purify water draining
into adjacent bodies of water, and to slow the flow of surface runoff
into lakes, rivers, and streams and thus prevent flooding and erosion.
In addition, adjacent wetlands may `serve significant natural
biological functions, including food chain production, general habitat,
and nesting, spawning, rearing and resting sites for aquatic . . .
species.' '' 447 U.S at 134 (citing 33 CFR 320.4(b)(2)(iv), (v), (vii)
(1985)).
    Wetlands with an unbroken surface or shallow subsurface connection
to jurisdictional waters are adjacent, including those wetlands that
directly abut a jurisdictional water (i.e., they are not separated by
uplands, a berm, dike, or similar barrier from the OHWM of the water to
which they are adjacent). All wetlands that directly abut
jurisdictional waters have an unbroken surface or shallow subsurface
connection because they physically touch the jurisdictional water. An
unbroken surface or shallow subsurface connection to jurisdictional
waters can also be established by a non-jurisdictional physical feature
or discrete conveyance that supports at least periodic flow between the
wetland and a jurisdictional water, such as a pipe, culvert, non-
jurisdictional ditch, or flood gate. Water does not have to be
continuously present in this hydrologic connection and the flow between
the wetland and the jurisdictional water may move in either or both
directions.
    A shallow subsurface hydrologic connection is predominantly lateral
water flow through a shallow subsurface layer. Such flows may be found,
for example, in wetlands on slopes, where water seeps through surface
soils to downstream waters, in soils with a restrictive horizon, in the
hyporheic zone, or in karst systems. A shallow subsurface connection
also exists, for example, when the adjacent wetland and the water to
which it is adjacent are in contact with the same shallow aquifer or
with the same shallow water table which fluctuates within the soil
profile, sometimes rising to or near the ground surface. Shallow
subsurface connections can also be maintained as water moves through
karst topography, and through confined human-made subsurface conveyance
systems such as drain tiles and storm sewers. Shallow subsurface
connections may be found below the ordinary root zone (below 12
inches), where other wetland delineation factors may not be present. A
variety of factors may reflect the presence of a shallow subsurface
connection, including position of the wetland in the landscape (for
example, on a slope above the jurisdictional waters), stream
hydrographs, soil surveys (for example, exhibiting indicators of high
transmissivity over an impermeable

layer), and information indicating that the water table in the stream
is lower than the shallow subsurface. The agencies may also utilize
direct observations in the field or tracer studies to demonstrate
shallow subsurface flow. Shallow subsurface connections convey water
quickly through the soil and impact surface water directly within hours
or days rather than the months or years it may take long pathways to
reach surface waters. However, neither shallow subsurface connections
nor any type of groundwater, shallow or deep, are themselves ``waters
of the United States.'' Some examples of wetlands that are adjacent
under the final rule due to an unbroken surface or shallow subsurface
connection include wetlands that are connected to a tributary via karst
topography, which provide a direct subsurface hydrologic connection
between the wetlands and the tributary and that is traceable via a dye
test, even if those wetlands are more than several hundred feet from
the tributary; and wetlands within a couple of hundred feet of a
tributary, where the subsurface hydrologic connection is demonstrated
via soil maps which demonstrate continuous hydric soils with indicators
of high transmissivity over an impermeable layer between the tributary
and the proximate wetlands. See Technical Support Document section
III.B.ii for additional information on surface and shallow subsurface
hydrologic connections.
    If a wetland is separated from a jurisdictional water by man-made
dikes or barriers, natural river berms, beach dunes, and the like, then
the wetlands are adjacent under this rule, consistent with the 1986
regulations. No additional identification of a hydrologic connection
between the wetland and the jurisdictional water is required for such
wetlands to be considered adjacent. For example, a wetland that is
separated from a jurisdictional tributary simply by a 40-foot road
meets the longstanding definition of adjacent. It is also important to
note that natural river berms are formed by sediment deposits
accumulating at or near stream banks during flood events. Such berms
vary in height from inches to feet, and also can be quite wide. With
respect to beach dunes and similar natural landforms, more than one
dune may exist between an adjacent wetland and jurisdictional water
(including primary and secondary dunes), because beach dunes typically
function as an interdunal system (particularly on barrier islands). For
example, interdunal wetlands which are located between dune ridges
would be adjacent.
    In some cases, a wetland may be separated from a jurisdictional
water by more than one human-made dike or barrier or multiple types of
barriers and landforms (e.g., a wetland separated by a human-made
barrier and a natural river berm). The agencies will assess such
wetlands consistent with the other adjacency criteria previously
described (i.e., by identifying the presence of an unbroken surface or
shallow subsurface connection or determining that their proximity to a
jurisdictional water is reasonably close).
    For purposes of determining whether a wetland is ``adjacent,''
artificial structures do not divide a wetland if a hydrologic
connection is maintained between the divided portions of the wetland.
Rather, the wetland is treated as one wetland. For example, if a
wetland is divided by a road, a culvert could maintain a hydrologic
connection. The agencies may also consider if a subsurface hydrologic
connection is maintained, using indicators such as hydric soils, the
permeability of the artificial structure, and/or the permeability of
the soils below the artificial structure.
    Wetlands are also adjacent when their proximity to a jurisdictional
water is reasonably close. The Supreme Court in Riverside Bayview
deferred to the Corps' judgment that adjacent wetlands ``that form the
border of or are in reasonable proximity to'' other ``waters of the
United States'' ``may be defined as waters under the Act.'' Riverside
Bayview, 474 U.S. at 134. Where the wetland is reasonably close to the
jurisdictional water, the agencies have concluded that ``adjacent
wetlands have significant effects on water quality and the aquatic
ecosystem.'' Id. at 135 n.9. The close proximity between an adjacent
wetland and a jurisdictional water means the wetland can modulate water
quantity and water quality in the jurisdictional water, and the
jurisdictional water can modulate water quantity and water quality in
the wetland. For example, wetlands typically help to store floodwaters,
pollutants, and sediments that could otherwise reach the jurisdictional
water to which they are adjacent. They can also provide flow
contributions to the jurisdictional waters to which they are adjacent
during high hydroperiods, where water spills from the wetland to the
nearby jurisdictional water, and such contributions of flow are
facilitated by the wetland's close proximity to the jurisdictional
water. The proximate jurisdictional waters can serve as important
sources of water for adjacent wetlands, for example, through
overtopping events where flow from the jurisdictional waters is stored
in the wetlands. While under this rule the agencies are not
establishing distance limits for adjacency, the agencies recognize that
as the distance between the wetland and jurisdictional water increases,
the reasonableness of the connection between the waters will generally
decrease, particularly in the absence of the type of surface or shallow
subsurface connections described above, and a finding of adjacency is
less likely. The distance between a jurisdictional water and its
adjacent wetlands may vary by region, as well as based on site-specific
factors within regions. In practice, under this criterion, the agencies
have found that adjacent wetlands are on the whole, nationwide, within
a few hundred feet of jurisdictional waters. This can vary from site to
site and region to region due to differences in climate, geomorphology,
landscape setting, hydrology, soils, vegetation, elevation, size of the
jurisdictional water, and other site-specific variables.
    Field data, including visual observations, can assist with
determining if a wetland is adjacent. In addition, a variety of remote
tools can help to assess adjacency, including maps, high-resolution
elevation data, aerial photographs, and high-resolution satellite
imagery. For example, visual observation, NWI and USGS topographic
maps, elevation data, and NHD data may identify a physical barrier or
illustrate the location of the traditional navigable water, territorial
sea, interstate water, paragraph (a)(2) impoundment, or jurisdictional
tributary; the wetland's proximity to the jurisdictional water; and the
nature of topographic relief between the two aquatic resources. Visual
observations, aerial photographs, or high-resolution satellite imagery
may illustrate hydrophytic vegetation from the boundary (e.g., OHWM for
non-tidal waters or high tide line for tidal waters) of the traditional
navigable water, the territorial seas, the interstate water, the
paragraph (a)(2) impoundment, or the jurisdictional tributary to the
wetland boundary, or the presence of water or soil saturation. Soil
samples or NRCS soil maps may identify the presence of hydric soil
types, soil saturation, or potential surface or subsurface hydrologic
connections. Additionally, methods that overlay depressions on the
landscape with hydric soils and hydrophytic vegetation can be used to
identify likely wetlands and hydrologic connections. Field work can
help

confirm the presence and location of the OHWM or high tide line of the
jurisdictional water and can provide additional information about the
wetland's potential adjacency to that water.\108\
---------------------------------------------------------------------------

    \108\ Field work may include, e.g., traversing the landscape
from the traditional navigable water, territorial sea, interstate
water, paragraph (a)(2) impoundment, or jurisdictional tributary to
the wetland and examining topographic and geomorphic
characteristics, as well as hydrologic and biologic indicators.
---------------------------------------------------------------------------

ii. Determining Whether an Adjacent Wetland Meets the Relatively
Permanent Standard
    Wetlands that are adjacent to paragraph (a)(1) waters are
jurisdictional without the need for further analysis. Wetlands adjacent
to paragraph (a)(2) impoundments and wetlands adjacent to
jurisdictional tributaries must meet a second requirement to be
jurisdictional as ``waters of the United States'' under this rule--they
must satisfy either the relatively permanent standard or the
significant nexus standard.
    Under this rule, adjacent wetlands meet the relatively permanent
standard if they have a continuous surface connection to a relatively
permanent paragraph (a)(2) impoundment or a jurisdictional tributary
when the jurisdictional tributary meets the relatively permanent
standard. As discussed previously in this section of this preamble,
wetlands that have a continuous surface connection to such waters are a
subset of adjacent wetlands. Wetlands that do not have a continuous
surface connection but are adjacent to paragraph (a)(2) impoundments or
jurisdictional tributaries will be evaluated for jurisdiction under the
significant nexus standard. See also section IV.C.5.c.iii of this
preamble.
    A continuous surface connection does not require a constant
hydrologic connection. Rather, the agencies will identify a continuous
surface connection consistent with the Rapanos plurality opinion, which
indicates that the continuous surface connection requirement is a
``physical-connection requirement.'' 547 U.S. at 751 n.13; see also
Rapanos Guidance at 7. Wetlands meet the continuous surface connection
requirement if they physically abut or touch a relatively permanent
paragraph (a)(2) impoundment or a jurisdictional tributary when the
jurisdictional tributary meets the relatively permanent standard.
Wetlands also meet the continuous surface connection requirement if
they are connected to relatively permanent waters by a discrete feature
like a non-jurisdictional ditch, swale, pipe, or culvert. This is
because a ditch or other such feature can serve as a physical
connection that maintains a continuous surface connection between an
adjacent wetland and a relatively permanent water. This approach to the
continuous surface connection is supported by the scientific
literature, case law, and the agencies' technical expertise and
experience. As the Court of Appeals for the Sixth Circuit has
explained, ``it does not make a difference whether the channel by which
water flows from a wetland to a navigable-in-fact waterway or its
tributary was manmade or formed naturally.'' United States v. Cundiff,
555 F.3d 200, 213 (6th Cir. 2009) (``Cundiff'') (holding wetlands were
jurisdictional under the Rapanos plurality where plaintiff created a
continuous surface connection by digging ditches to enhance the acid
mine drainage into the creeks and away from his wetlands).
    Similarly, a natural berm, bank, dune, or similar natural landform
between an adjacent wetland and a relatively permanent water does not
sever a continuous surface connection to the extent it provides
evidence of a continuous surface connection. This approach is
consistent with the agencies' interpretation in the 2020 NWPR that
natural berms and similar natural landforms ``are indicators of a
direct hydrologic surface connection as they are formed through
repeated hydrologic events.'' 85 FR 22311 (April 21, 2020). As the 2020
NWPR explained, ``a natural river berm can be created by repeated
flooding and sedimentation events when a river overtops its banks and
deposits sediment between the river and a wetland.'' Id. (citing
Science Report at A-7). The 2020 NWPR noted that the adjacent wetland
could have been formed at the same time as or after the formation of
the natural river berm due to repeated flooding and the impeded return
flow created by the berm. Natural banks can also provide evidence of a
continuous surface connection because the processes that result in
their formation can also be representative of the interconnected
relationship between the wetlands and the relatively permanent water.
Adjacent wetlands may be separated by a bank from a relatively
permanent water due to an elevation difference between the bank and the
water (e.g., when the stream is incised). The surface water flow of a
tributary over time can erode a channel, which creates a bank
separating the tributary from the adjacent wetland. See 85 FR 22311
(April 21, 2020). In addition, the presence of a beaver dam between a
wetland and a relatively permanent water can be evidence of a
continuous surface connection between the two features, even if the dam
itself blocks surface hydrologic flow for periods of time. Beach dunes
may also separate adjacent wetlands and relatively permanent waters.
Beach dunes are sometimes formed through wind erosion which results in
the sand surface interacting with the water table, providing enough
hydrology to create wetlands. Beach dunes may also be formed when water
levels drop in lakes or from historic glacial retreat. Many interdunal
wetlands have seasonally variable hydroperiods where they may be dry
during periods of low rainfall. All of these processes and the
resulting natural berm, bank, dune, or similar natural landform
indicate that the wetlands are integrated and ``inseparably bound up''
with the relatively permanent waters. See 85 FR 22280 (April 21, 2020)
(citing Rapanos, 547 U.S. at 732 (Scalia, J., plurality opinion)). The
agencies recognize that not all natural berms, banks, dunes, and
similar natural landforms demonstrate evidence of a continuous surface
connection. For example, an adjacent wetland may be separated from a
relatively permanent water by a relict landform like a natural berm
that no longer interacts hydrologically with the tributary network.
Such relict barriers do not demonstrate evidence of a continuous
surface connection and may in fact sever the continuous surface
connection.
    While natural barriers may at times occur within a floodplain, the
existence of a floodplain (and other land masses similar to a
floodplain, such as a riparian area or fluvial terrace) generally is
not sufficient to indicate a continuous surface connection. Wetlands
separated from jurisdictional waters by cliffs, bluffs, or canyon walls
also typically do not have a continuous surface connection, and thus
would be assessed under the significant nexus standard. However, if
these cliffs, bluffs, or canyon walls have gaps or built structures
(e.g., culverts, pipes, or waterfalls) that provide for a continuous
surface connection between the adjacent wetlands and the relatively
permanent water, this type of connection would satisfy the physical
connection requirement for a continuous surface connection. The same is
true for dikes or other artificial barriers with gaps or structural
components that allow for a continuous surface connection. For example,
an upland levee that separates an adjacent wetland from a tributary
that is relatively permanent may have gaps along the length of the
levee that

provide for a physical connection between the wetlands and the
tributary that satisfies the requirement for a continuous surface
connection.
    Some commenters asserted that the agencies' use of the relatively
permanent standard in the proposed rule is inconsistent with the
Rapanos plurality opinion because it does not require a continuous
hydrologic connection for adjacent wetlands to be jurisdictional, with
one commenter referencing the agencies' statement in the proposed rule
that a continuous surface connection ``does not require surface water
to be continuously present between the wetland and the tributary.''
Another commenter asserted that the proposed rule's approach to
adjacent wetlands is inconsistent with the Rapanos plurality opinion
because it allows for the continuous surface connection requirement to
be satisfied by physical connections such as non-jurisdictional ditches
with an irregular flow surface connection requirement. The agencies
disagree that the approach in this rule is inconsistent with the
plurality opinion. The plurality opinion indicates that ``continuous
surface connection'' is a ``physical connection requirement.'' Rapanos,
547 U.S. at 751 n.13 (referring to ``our physical-connection
requirement'' and later stating that Riverside Bayview does not reject
``the physical-connection requirement''). This approach to the
continuous surface connection requirement is consistent with the
Rapanos Guidance. Rapanos Guidance at 7 & n.28. A continuous surface
connection is not the same as a continuous surface water connection, by
its terms and in effect. Therefore, because the plurality opinion
requires only a ``continuous surface connection,'' the relatively
permanent standard in this rule, consistent with the plurality opinion,
does not require surface water to be continuously present between the
wetland and the tributary. The agencies also disagree that it is
inconsistent with the plurality opinion for adjacent wetlands to be
considered to meet the continuous surface connection requirement if
they are connected to relatively permanent waters by a discrete feature
like a non-jurisdictional ditch, swale, pipe, or culvert. This is
because a ditch or other such feature can serve as a physical
connection that maintains a continuous surface connection between an
adjacent wetland and a relatively permanent water. This approach to the
continuous surface connection is supported by the scientific
literature, case law, and the agencies' technical expertise and
experience. See Cundiff, 555 F.3d at 213.
    The agencies agree with commenters who stated that a continuous
surface connection does not require the continuous presence of surface
water between the adjacent wetland and relatively permanent paragraph
(a)(2) impoundment or jurisdictional tributary when the jurisdictional
tributary meets the relatively permanent standard, and the agencies
continue this longstanding approach in this rule. The agencies'
approach is consistent with science, as well as the longstanding
regulatory definition of ``wetlands,'' which does not require such
aquatic resources to contain surface water. See 33 CFR 328.3(b)(2014)
and 40 CFR 232.2 (2014)(defining wetlands as ``areas that are inundated
or saturated by surface or ground water at a frequency and duration
sufficient to support a prevalence of vegetation typically adapted for
life in saturated soil conditions'' (emphasis added)); see also
Technical Support Document section III.B. Since wetlands frequently do
not contain surface water, a requirement for continuous surface water
between a relatively permanent water and adjacent wetlands would be
illogical as a scientific and practical matter.
    The agencies have a variety of tools for determining whether
adjacent wetlands have a continuous surface connection to relatively
permanent waters, or if they are separated from them by natural
landforms or artificial barriers, including the same tools used to
establish adjacency. Visual observations, high-resolution satellite
imagery, NRCS soil maps, USGS topographic maps, and NHD data may show
soil saturation, surface flow patterns and infrastructure crossings
(e.g., roads) that can be used to indicate possible culvert locations.
Visual observations, high-resolution satellite imagery, elevation data
such as LIDAR-based topographic models, and USGS topographic maps may
identify the presence of swales that are located between a wetland and
a relatively permanent water. Similar tools (described below) and
visual observations can be used to identify the potential presence of
natural landforms that can maintain a continuous surface connection and
the potential presence of breaks that may sever a continuous surface
connection. Distinguishing between landforms like upland breaks and
natural berms can be facilitated by assessing their linear extent and
continuity, or observations on how they hydrologically interact with an
associated relatively permanent water.
    To assess whether wetlands are separated from relatively permanent
waters by natural landforms or artificial barriers, the agencies can
rely upon a variety of tools. For example, USGS topographic maps may
show topographic highs between the wetland and relatively permanent
water, or simple indices can be calculated based on topography to
indicate where these separations occur and their linear extent. FEMA
flood zone or other floodplain maps may indicate constricted
floodplains along the length of the tributary channel with physical
separation of flood waters. High-resolution elevation data can
illustrate topographic highs between a wetland and tributary channel
that extend along the length of a tributary's channel. Aerial
photographs or high-resolution satellite imagery may illustrate upland
vegetation along the tributary channel between the wetland and
tributary channel, or bright soil signatures indicative of higher
ground. NRCS soil maps may identify mapped linear, upland soil types
along the tributary channel. Field work may help to confirm the
presence and location of the OHWM of a tributary that is relatively
permanent. In addition, field work may confirm whether there is a
continuous physical connection between the wetland and the tributary,
or identify breaks that may sever the continuous surface
connection.\109\
---------------------------------------------------------------------------

    \109\ Field work may include, e.g., traversing the landscape
from the tributary to the wetland and examining topographic and
geomorphic characteristics, the linear extent of those features, as
well as hydrologic and biologic indicators.
---------------------------------------------------------------------------

iii. Determining Whether an Adjacent Wetland Meets the Significant
Nexus Standard
    The agencies note again that the determination of adjacency and the
determination of a significant nexus are different and that there are
two key differences. First, adjacency is about the relationship between
a wetland and a jurisdictional water and is based on reasonable
proximity, whereas significant nexus is about the functions provided by
an adjacent wetland to a paragraph (a)(1) water-the significant nexus
assessment is not to the jurisdictional water to which the wetland is
adjacent (if the jurisdictional water is a paragraph (a)(1) water, it
is jurisdictional without a case-specific significant nexus
assessment). Second, a wetland must meet the adjacency standard on its
own, whereas a significant nexus assessment is based on whether an
adjacent wetland alone or in combination with other similarly situated
waters significantly affects the

integrity of a paragraph (a)(1) water. Once a wetland has been
determined to be ``adjacent,'' if the adjacent wetland does not meet
the relatively permanent standard, the agencies will conduct a
significant nexus analysis to assess if the wetland is jurisdictional.
    Under the regulations, the adjacent wetlands which do not meet the
relatively permanent standard and for which a significant nexus
analysis must be conducted are: (1) adjacent wetlands that lack a
continuous surface connection to a relatively permanent paragraph
(a)(2) impoundment or a jurisdictional tributary when the
jurisdictional tributary meets the relatively permanent standard, and
(2) wetlands adjacent to a paragraph (a)(2) impoundment or a tributary
when the paragraph (a)(2) impoundment or the tributary is not
relatively permanent. In evaluating such adjacent wetlands under the
significant nexus standard, the agencies will determine whether the
wetlands, either alone or in combination with similarly situated waters
in the region, significantly affect the chemical, physical, or
biological integrity of paragraph (a)(1) waters. See section IV.C.9 of
this preamble for additional discussion on the definition of
``significantly affect'' in this rule, including the factors that will
be evaluated and the functions that will be assessed as part of a
significant nexus analysis. The agencies consider tributaries and their
adjacent wetlands to be ``similarly situated'' waters. The agencies
consider similarly situated waters to be ``in the region'' when they
lie within the catchment area of the tributary of interest. Therefore,
in implementing the significant nexus standard under this rule, all
tributaries and adjacent wetlands within the catchment area of the
tributary of interest will be analyzed as part of the significant nexus
analysis.
    For a significant nexus analysis, the region would be the catchment
that drains to and includes the tributary to which the wetland in
question is adjacent. A catchment is the area of the land surface that
drains to a specific location for a specific hydrologic feature, such
as a tributary. Catchments will be delineated from the downstream-most
point of the tributary reach to which the wetland is adjacent and
include the land uphill that drains to that point, as discussed in
further detail in section IV.C.4.c of this preamble and its
subsections.
    After identifying the catchment, the next step is to identify the
tributaries within the catchment under the agencies' longstanding
interpretation of tributary, see section IV.C.4.a of this preamble, and
their adjacent wetlands within the catchment area, see section
IV.C.5.c.i of this preamble. When evaluating whether an adjacent
wetland meets the significant nexus standard, the agencies will
consider the factors in the final rule, along with the functions of the
tributaries in the catchment together with the functions performed by
the wetlands adjacent to the tributaries in the catchment, including
the subject wetland, in relation to the chemical, physical, or
biological integrity of the paragraph (a)(1) water. This approach to
the significant nexus analysis recognizes the ecological relationship
between wetlands and the tributaries to which they are adjacent, and
the role those similarly situated waters have in influencing the
chemical, physical, or biological integrity of paragraph (a)(1) waters.
See Technical Support Document section III.E.
    Section IV.C.9.c of this preamble discusses a variety of tools and
sources of information that can be used to assess significant effects
on the chemical, physical, and biological integrity of paragraph (a)(1)
waters. Remote tools, field indicators and observational methods, and
datasets can all assist in determining whether adjacent wetlands meet
the significant nexus standard. In addition, a variety of modeling
approaches can be used to quantify the connectivity and cumulative
effects of wetlands, including non-floodplain wetlands, on other
waters, as discussed further in section IV.A.v of the Technical Support
Document.\110\
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    \110\ Some examples include the Soil and Water Assessment Tool
(SWAT, available at https://swat.tamu.edu/), the Hydrologic
Simulation Program in Fortran (available at https://www.epa.gov/ceam/hydrological-simulation-program-fortran-hspf), and DRAINMOD for
Watersheds (DRAINWAT, available at https://www.bae.ncsu.edu/agricultural-water-management/drainmod/). Other examples of models
applicable to identifying effects of wetlands on downstream waters
include the USGS hydrologic model MODFLOW (available at https://www.usgs.gov/mission-areas/water-resources/science/modflow-and-related-programs?qt-science_center_objects=0#qt-science_center_objects) and the USGS flow simulation model VS2DI
(available at https://www.usgs.gov/software/vs2di-version-13).
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6. Waters Not Identified in Paragraphs (a)(1) Through (4)
a. This Rule
    Paragraph (a)(5) of this rule defines ``waters of the United
States'' to include ``intrastate lakes and ponds, streams, or wetlands
not identified in paragraphs (a)(1) through (4)'' that meet either the
relatively permanent standard or the significant nexus standard. Waters
in this category in the 1986 regulations were sometimes referred to as
``(a)(3) waters'' or ``other waters.'' With this rule, the agencies
have made important changes to the 1986 regulations to reflect the
agencies' construction of the statutory limits on the scope of ``waters
of the United States'' informed by the relevant provisions of the Clean
Water Act and the statute as a whole, the scientific record, relevant
Supreme Court precedent, and the agencies' experience and technical
expertise after more than 45 years of implementing the longstanding
pre-2015 regulations defining ``waters of the United States.'' Of
particular importance, the agencies have replaced the broad Commerce
Clause basis for jurisdiction from the 1986 regulations for waters not
identified in other provisions of the definition with the relatively
permanent standard and the significant nexus standard. Because the
relatively permanent standard and the significant nexus standard
require connections to a paragraph (a)(1) water, and the significant
nexus standard further requires that waters significantly affect
paragraph (a)(1) waters, this provision of the rule is substantially
narrower than the 1986 regulations. The 1986 regulations, for example,
authorized the assertion of jurisdiction over waters from which fish or
shellfish are or could be taken and sold in interstate or foreign
commerce.
    The agencies are including a provision for intrastate lakes and
ponds, streams, or wetlands not identified in paragraphs (a)(1) through
(4) of the rule because such waters can provide functions that restore
and maintain the chemical, physical, and biological integrity of
traditional navigable waters, the territorial seas, and interstate
waters. See section IV.A.2.c.iii of this preamble. For example, a large
lake that is very close to a tributary or paragraph (a)(1) water, but
that is not part of the tributary system, would be non-jurisdictional
if the agencies did not include the category for assessing such waters
under paragraph (a)(5) in this rule, even if that lake provides many
functions that significantly affect a traditional navigable water.
    The agencies have streamlined and clarified the provision for
paragraph (a)(5) waters as compared to the 1986 regulations. The
agencies have added the requirement that these waters must meet either
the relatively permanent standard or significant nexus standard to be
``waters of the United States.'' In addition, the agencies have deleted
the non-exclusive list of ``other waters'' that was featured in
paragraph (a)(3) of the 1986 regulations. Under the final rule's new
paragraph (a)(5) provision, only ``intrastate lakes and ponds, streams,
or wetlands not identified in paragraphs

(a)(1) through (4)'' can be assessed for jurisdiction under the
relatively permanent standard or significant nexus standard. As
discussed further below, however, the agencies have concluded that the
more specific water types previously listed in paragraph (a)(3) of the
1986 regulations nonetheless generally fall within one of the four
water types listed in paragraph (a)(5) of this rule.
    Finally, the agencies have moved the provision for paragraph (a)(5)
waters to the end of the section of the regulation which defines the
categories of jurisdictional waters, since paragraph (a)(5) waters are
those that are not covered by the preceding categories. As a result,
``other waters'' are now in paragraph (a)(5) of this rule. In light of
these changes to the regulatory text, the agencies refer to these
waters as ``those not identified in paragraphs (a)(1) through (4)'' or
``paragraph (a)(5) waters'' for purposes of this rule.
    Waters assessed under paragraph (a)(5) meet the relatively
permanent standard if they are relatively permanent, standing or
continuously flowing bodies of water with a continuous surface
connection to a paragraph (a)(1) water or a tributary that is
relatively permanent. The agencies will assess waters under paragraph
(a)(5) to determine if they are relatively permanent using a similar
approach to the one described for tributaries in section IV.C.4 of this
preamble, and the agencies will assess a continuous surface connection
between waters assessed under paragraph (a)(5) and a paragraph (a)(1)
water or a tributary that is relatively permanent using the approach
described for adjacent wetlands in section IV.C.5 of this preamble.
Waters assessed under paragraph (a)(5) meet the significant nexus
standard if they significantly affect the chemical, physical, or
biological integrity of a traditional navigable water, the territorial
seas, or an interstate water. See section IV.C.6.c of this preamble for
further discussion on implementation of these standards for waters
assessed under paragraph (a)(5). The agencies also note that the
characteristics of a water considered for jurisdiction under paragraph
(a)(5) can change over time such that it meets the requirements for
consideration under another category of ``waters of the United
States.'' For example, a river that does not drain to a paragraph
(a)(1) water could potentially become a traditional navigable water,
for instance, if it is impounded and becomes a navigable-in-fact
reservoir. Such water would then be assessed as a traditional navigable
water under paragraph (a)(1)(i) of the final rule. Similarly, a wetland
that historically was not adjacent can become an adjacent wetland, for
example, if a ditch is constructed that connects the wetland to a
jurisdictional tributary. Such a wetland would then be considered under
paragraph (a)(4) of the final rule due to the unbroken surface
connection to a jurisdictional water via the ditch.
b. Summary of the Agencies' Consideration of Public Comments and
Rationale for This Rule
    The agencies received numerous comments on whether to include a
category for waters that do not fall within one of the more specific
categories in the definition of ``waters of the United States'' and the
standard upon which to base jurisdiction over such waters, as well as
on implementation of this provision of the rule.
i. Comments on the Provision for Waters That Do Not Fall Within One of
the More Specific Categories
    Some commenters expressed general support for including a category
for waters that do not fall within one of the more specific categories
in this rule, while others opposed including such a category. Many
commenters requested clarification of the category for waters that do
not fall within one of the more specific categories. Many commenters
addressed the agencies' legal authority to assert jurisdiction over
waters that do not fall within one of the more specific categories.
Some commenters asserted that following the Supreme Court's decisions
in SWANCC and Rapanos, the agencies lack authority to assert
jurisdiction over such waters. Other commenters stated that the
proposed rule's approach to such waters is legally defensible. Several
commenters further stated that the proposed rule does not go far enough
in protecting waters that do not fall within one of the more specific
categories and asserted that broader protection would be consistent
with Rapanos, SWANCC, and Maui.
    The agencies disagree that the agencies lack authority to assert
jurisdiction over waters that do not fall within one of the more
specific categories. The agencies' regulations have long had provisions
for case-specific determinations of jurisdiction over waters that did
not fall within the other jurisdictional categories. See section
IV.A.2.b of this preamble. Such waters under this rule can be assessed
under paragraph (a)(5), and they are only jurisdictional if they meet
the relatively permanent standard or significant nexus standard. The
agencies have thus established limits on the scope of these waters
consistent with the law, the science, and agency expertise. See section
IV.A of this preamble. In addition, the agencies have carefully
considered the limitations on their authority under the Clean Water
Act, especially concerning paragraph (a)(5) waters. The agencies have
made a number of changes to the 1986 regulations that collectively
ensure the definition of ``waters of the United States'' remains well
within statutory and constitutional limits. Those changes include
replacing the broad Commerce Clause basis for jurisdiction over
paragraph (a)(5) waters with the narrower relatively permanent and
significant nexus standards, eliminating jurisdiction over tributaries
and adjacent wetlands based on their connection to paragraph (a)(5)
waters, and eliminating jurisdiction by rule over impoundments of
paragraph (a)(5) waters. See sections IV.A.3.a.i, IV.C.3, IV.C.4, and
IV.C.5 of this preamble. In addition, as discussed further in the
implementation section below, the agencies are intending to continue a
thoughtful, careful approach to implementation and coordination for
paragraph (a)(5) waters.
    The agencies also received numerous comments on the standard to be
used for determining jurisdiction over waters that do not fall within
one of the more specific categories. Some commenters supported the
proposed rule's requirement that such waters meet either the relatively
permanent standard or the significant nexus standard. However, other
commenters did not support this approach. One commenter recommended
that the agencies not apply the relatively permanent standard to waters
that do not fall within one of the more specific categories because it
would be duplicative. Specifically, the commenter asserted that waters
that meet the relatively permanent standard as described in the
proposed rule would always meet the jurisdictional criteria for another
rule category. A few commenters disagreed with applying the significant
nexus standard to waters that do not fall within one of the more
specific categories, asserting that it goes beyond the scope of
jurisdiction contemplated by Justice Kennedy in Rapanos. Many other
commenters opposed the proposed rule's removal of the interstate and
foreign commerce jurisdictional basis for protecting waters that do not
fall within one of the more specific categories. Commenters expressed
that this basis would protect many important waterways which provide
valuable public health,

agricultural, recreational, drinking water, ecological, and economic
services important to local, regional, and national interests.
    Under the 1986 regulations, ``other waters'' (such as intrastate
rivers, lakes, and wetlands that were 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 rule amends the 1986
regulations to delete all the provisions referring to authority over
activities that ``could affect interstate or foreign commerce'' and
replaces them with the relatively permanent and significant nexus
standards. Thus, this rule would provide for case-specific analysis of
waters not addressed by any other provision of the definition to
determine whether they are ``waters of the United States'' under the
relatively permanent or significant nexus standards.
    The text of the 1986 regulations reflected the agencies'
interpretation at the time, based primarily on the legislative history
of the Clean Water Act, that the jurisdiction of the Act extended to
the maximum extent permissible under the Commerce Clause of the
Constitution. While SWANCC did not invalidate the 1986 regulations'
``other waters'' provision or any other parts of the 1986 regulations'
definition of ``waters of the United States,'' the Court cautioned that
that it ``assum[es] that Congress does not casually authorize
administrative agencies to interpret a statute to push the limit of
congressional authority.'' 531 U.S. at 172-73. Therefore, the agencies
conclude that asserting jurisdiction over non-navigable, intrastate
waters based solely on whether the use, degradation, or destruction of
the water could affect interstate or foreign commerce pushes the limit
of the Clean Water Act where those waters do not significantly affect
paragraph (a)(1) waters. This rule thus replaces the interstate
commerce test with the relatively permanent and significant nexus
standards. As discussed in section IV.A of this preamble, the agencies
have concluded that the significant nexus standard is consistent with
the statutory text and legislative history, advances the objective of
the Clean Water Act, is informed by the scientific record and Supreme
Court case law, and appropriately considers the policies of the Act.
The relatively permanent standard is included in the rule because it
provides important efficiencies and additional clarity for regulators
and the public by more readily identifying a subset of waters that will
virtually always significantly affect paragraph (a)(1) waters. Thus,
this rule gives effect to the Clean Water Act's broad terms and
environmentally protective aim as well as its limitations.
    Accordingly, waters that do not fall within one of the more
specific categories identified in paragraphs (a)(1) through (4) of this
rule may still be jurisdictional. This is consistent with the text of
the statute, relevant Supreme Court case law, and the science. See
section IV.A of this preamble and Technical Support Document section
III.D. The Rapanos plurality concluded, ``relatively permanent,
standing or continuously flowing bodies of water,'' 547 U.S. at 739,
that are connected to traditional navigable waters, id. at 742, and
waters with a ``continuous surface connection'' to such water bodies,
id. (Scalia, J., plurality opinion), are ``waters of the United
States'' under the relatively permanent standard. Without paragraph
(a)(5), a relatively permanent lake that is not a tributary and is not
a wetland, but which nonetheless has a continuous surface connection to
a traditional navigable water, could not be evaluated for jurisdiction.
Justice Kennedy concluded that SWANCC held that ``to constitute `
``navigable waters'' ' under the Act, a water or wetland must possess a
`significant nexus' to waters that are or were navigable in fact or
that could reasonably be so made.'' Id. at 759 (citing SWANCC, 531 U.S.
at 167, 172). Many lakes and ponds that are not part of the tributary
system and that do not qualify as a paragraph (a)(1) water can only be
assessed under paragraph (a)(5) of this rule. There is no basis in the
statute or the science for excluding a lake or pond from the definition
of ``waters of the United States'' that is situated on the landscape in
a similar manner as an adjacent wetland, solely because it is a lake
and not a wetland.
    Multiple commenters stated that the proposed rule's inclusion of
waters that do not fall within one of the more specific categories
would impermissibly assert jurisdiction over a wide range of features
that are far from traditional navigable waters and that have only minor
volumes of flow. A few commenters suggested that although the proposed
rule recognizes the importance of the strength of connection,
particularly the distance of such waters to navigable waters, it
suggests that the agencies may rely too much on scientific principles
when making jurisdictional determinations in a manner that improperly
expands the scope of the agencies' authority. Another commenter
asserted that the agencies should not consider water functions that
indicate isolation between water features as a basis for finding a
significant nexus for waters that do not fall within one of the more
specific categories.
    The agencies disagree that this rule's category for waters that do
not fall within one of the more specific categories, paragraph (a)(5),
improperly expands the scope of their authority. The agencies have not
only narrowed this category from the 1986 regulations by replacing the
broad Commerce Clause provisions with the relatively permanent standard
and the significant nexus standard, but they have also made additional
changes from the 1986 regulations in order to ensure that they are not
pushing the outer limits of the authority granted to them by Congress
under the Clean Water Act. See section IV.A.3.a.i of this preamble.
Impoundments of waters jurisdictional under paragraph (a)(5) no longer
remain jurisdictional by rule. Tributaries to waters jurisdictional
under paragraph (a)(5) are not tributaries under paragraph (a)(3) of
this rule and must themselves be assessed under paragraph (a)(5).
Wetlands adjacent to waters jurisdictional under paragraph (a)(5) are
not adjacent wetlands under paragraph (a)(4) of this rule and must
themselves be assessed under paragraph (a)(5). In addition, as
discussed further below, the agencies have established enhanced
coordination procedures for waters assessed under the significant nexus
standard under paragraph (a)(5) in order to ensure that such