information about the federalism consultation can be found in section
V.E of this preamble and the Summary

Report of Federalism Consultation, available in the docket for this
rule.
    The agencies initiated a Tribal consultation and coordination
process during development of the proposed rule which was conducted
over a 66-day period from July 30, 2021, until October 4, 2021,
including two consultation kick-off webinars. The agencies received
consultation comment letters from 27 Tribes and three Tribal
organizations and held three leader-to-leader consultation meetings and
four staff-level meetings with Tribes at their request. On October 7,
13, 27, and 28, 2021, the agencies hosted virtual dialogues with Tribes
focused on implementation of prior ``waters of the United States''
regulatory regimes. Additional information about Tribal consultation
and engagement can be found in section V.F of this preamble and the
Summary of Tribal Consultation and Coordination, which is available in
the docket for this rule.
    The agencies signed a proposed rule defining ``waters of the United
States'' on November 18, 2021. On December 7, 2021, the agencies
published the proposed rulemaking in the Federal Register, 86 FR 69372,
which initiated a 60-day public comment period that lasted through
February 7, 2022. EPA and Army held three virtual public hearings on
January 11, 13, and 18, 2022. The Office of Advocacy of the U.S. Small
Business Administration hosted EPA and Army staff in January 2022 to
discuss the proposed rule with small entities at its Small Business
Environmental Roundtables. The agencies met with small agricultural
interests and their representatives for a roundtable on January 7,
2022, and met with other small entities on January 10, 2022. The
agencies also engaged with State and local governments during the
public comment period, including through two virtual roundtables on
January 24 and 27, 2022. The agencies continued to engage with Tribes
during the public comment period. On January 20, 2022, the agencies
hosted a Tribal virtual roundtable.
    In developing this rule, the agencies reviewed and considered
approximately 114,000 comments received on the proposed rulemaking from
a broad spectrum of interested parties. Commenters provided a wide
range of feedback on the proposal, including: the legal basis for the
proposed rule; the agencies' proposed treatment of categories of
jurisdictional waters and those features that would not be
jurisdictional; the Economic Analysis and Technical Support Document
for the proposed rule; and the need for a clear and implementable rule
that is easy for the public to understand. The agencies discuss
comments received and their responses in the applicable sections of the
preamble to this rule. A complete response to comments document is
available in the docket for this rule (Docket ID No. EPA-HQ-OW-2021-
0602).
    The agencies also engaged with EPA's Science Advisory Board (SAB)
on several occasions during the development of this rule. The SAB was
established in 1978 by the Environmental Research, Development, and
Demonstration Authorization Act (ERDDAA), to provide independent
scientific and technical advice to the EPA Administrator on the
technical basis for agency positions and regulations.
    On January 28, 2022, during the public comment period, the agencies
met with the SAB Work Group for Review of Science Supporting EPA
Decisions to explain the proposed rule, including its basis, and to
address the SAB Work Group's initial questions. On February 7, 2022,
the SAB Work Group signed a memorandum recommending that the Chartered
SAB should review the adequacy of the science supporting the proposed
rule. SAB Memorandum: Recommendations of the SAB Work Group for Review
of Science Supporting EPA Decisions Regarding Two Planned EPA
Regulatory Actions (February 7, 2022). On March 7, 2022, during the
public meeting of the Chartered SAB, the Chartered SAB unanimously
voted to review the scientific and technical basis of the proposed
rule. The SAB formed a Work Group of its chartered members which issued
a draft review on May 9, 2022, and the Chartered SAB held public
meetings on the matter on May 31 and June 2, 2022. The SAB issued their
final review on July 5, 2022 (EPA-SAB-22-005, hereinafter, ``2022 SAB
Review''). All materials related to the SAB's review are available in
the docket for this rule and on the SAB's website.
    The SAB's review of the proposed rule was overall supportive of the
science underpinning the proposed rule, including the Technical Support
Document, and the discussion of shallow subsurface flow. The SAB made
some recommendations on the discussion of climate change. The SAB's
review was also generally favorable towards the approaches taken in the
Economic Analysis supporting the proposed rule. The SAB made
recommendations for improvement of the Economic Analysis, particularly
regarding the environmental federalism approach and the continued non-
monetization of certain benefits. The SAB indicated that the agencies'
plans for expanding the environmental justice analysis for this rule
were appropriate and provided recommendations for improving and
clarifying the analysis. A memorandum summarizing the agencies'
interactions with the SAB and the SAB's review of the proposed rule is
available in the docket for this rule.

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

A. Basis for This Rule

    In this rule, the agencies are exercising their authority to
interpret ``waters of the United States'' to mean the waters defined by
the familiar 1986 regulations, with amendments to reflect the agencies'
determination 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, 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.'' \43\ The agencies construe the term ``waters of the United
States'' to mean: (1) traditional navigable waters, the territorial
seas, and interstate waters (``paragraph (a)(1) waters''); (2)
impoundments of ``waters of the United States'' (``paragraph (a)(2)
impoundments''); (3) tributaries to traditional navigable waters, the
territorial seas, interstate waters, or paragraph (a)(2) impoundments
when the tributaries meet either the relatively permanent standard or
the significant nexus standard (``jurisdictional tributaries''); (4)
wetlands adjacent to paragraph (a)(1) waters; 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
wetlands adjacent to paragraph (a)(2) impoundments or jurisdictional
tributaries when the wetlands meet the significant nexus standard
(``jurisdictional adjacent wetlands'');

and (5) 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 (``paragraph
(a)(5) waters''). This rule also contains, at paragraph (b), the
longstanding exclusions in the 1986 regulations, as well as additional
exclusions based on well-established practice, from the definition of
``waters of the United States'' and, at paragraph (c), definitions for
terms used in this rule.
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    \43\ For brevity, the agencies may refer to the considerations
that formed the basis of the agencies' interpretation of ``waters of
the United States'' in the final rule as ``the law, the science, and
agency expertise.'' References to the agencies' consideration of
``the law, the science, and agency expertise'' throughout this
preamble are intended to encompass the agencies' consideration of
the text of the relevant provisions of the Clean Water Act and the
statute as a whole, the scientific record, relevant Supreme Court
decisions, and the agencies' experience and technical expertise
implementing the pre-2015 regulatory regime.
---------------------------------------------------------------------------

    This rule advances the Clean Water Act's statutory objective to
``restore and maintain the chemical, physical, and biological integrity
of the Nation's waters,'' section 101(a), as it is informed by the best
available science concerning the functions provided by upstream
tributaries, adjacent wetlands, and paragraph (a)(5) waters to restore
and maintain the water quality of paragraph (a)(1) waters. In
developing the rule, the agencies also considered the text of the
relevant statutory provisions of the Clean Water Act and the statute as
a whole, relevant Supreme Court case law, and the agencies' experience
and technical expertise after more than 45 years of implementing the
1986 regulations defining ``waters of the United States,'' including
more than a decade of experience implementing those regulations
consistent with the decisions in Riverside Bayview, SWANCC, and Rapanos
collectively.
    This construction also reflects consideration of provisions of the
Clean Water Act referencing the role of the States. Section 101(b)
provides that ``[i]t is the policy of the Congress to recognize,
preserve, and protect the primary responsibilities and rights of States
to prevent, reduce, and eliminate pollution, to plan the development
and use (including restoration, preservation, and enhancement) of land
and water resources.'' The provisions in this rule reflect
consideration of the comprehensive nature and objective of the Clean
Water Act and also avoid assertions of jurisdiction that raise
federalism concerns. Determining where to draw the boundaries of
Federal jurisdiction to ensure that the agencies advance Congress's
objective while preserving and protecting the responsibilities and
rights of the States is assigned by Congress to the agencies. This
rule's relatively permanent and significant nexus limitations
appropriately draw this boundary by ensuring that where upstream waters
significantly affect the integrity of the traditional navigable waters,
the territorial seas, and interstate waters, Clean Water Act programs
will apply to ensure that those downstream waters have a baseline of
protection established by Federal law. Where they do not, Tribes and
States have authority. These limitations are based on the agencies'
conclusion 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, and
that, while the relatively permanent standard, standing alone,
identifies only a subset of the ``waters of the United States,''
including this standard in the final rule facilitates ease of
implementation. In addition, this rule reflects consideration of the
agencies' experience and expertise, as well as updates in
implementation tools and resources, and its terms are generally
familiar and implementable.
    For all these reasons, this rule will achieve the agencies' goals
of effectively and durably protecting the quality of the nation's
waters. The effectiveness of this rule is based, in part, on the
familiarity of the regulatory framework to the agencies and
stakeholders, with an array of readily available tools and resources.
This rule also is durable because it is founded on the familiar
framework of the longstanding 1986 regulations, amended to reflect the
agencies' interpretation of appropriate limitations on the geographic
scope of the Clean Water Act in light of the law, the science, and
agency expertise. This rule also reflects the agencies' consideration
of the extensive public comments. This rule protects the quality of the
nation's waters by restoring the important protections for
jurisdictional waters provided by the Clean Water Act, including not
only protections provided by the Act's permitting programs, but also
protections provided by programs ranging from water quality standards
and total maximum daily loads to oil spill prevention, preparedness,
and response programs, to the Tribal and State water quality
certification programs.
1. The Agencies Are Exercising the Authority Granted by Congress To
Define ``Waters of the United States'' Under the Clean Water Act
    The agencies are exercising the authority granted to them by
Congress in the Clean Water Act to construe the key term ``navigable
waters,'' which Congress broadly defined to mean ``the waters of the
United States, including the territorial seas.'' 33 U.S.C. 1362(7)
(Clean Water Act section 502(7)). As explained herein, the text of the
statute, including in particular sections 501 and 502(7), and
congressional intent provide that delegation of authority. And the
Supreme Court has affirmed the conclusion that the agencies have the
authority to define the bounds of ``waters of the United States.'' In
this rule, the agencies are using the traditional tools of statutory
construction to exercise their delegated authority. Further, the rule
is founded upon the longstanding 1986 regulations, familiar to Congress
and the Court, while incorporating important limitations based on the
text of the statute. Finally, it is well established that agencies have
inherent authority to reconsider past decisions and to revise, replace,
or repeal a decision to the extent permitted by law and supported by a
reasoned explanation.
    Congress's intent to delegate authority to the agencies to construe
the term ``navigable waters'' and its definition in section 502(7),
``the waters of the United States, including the territorial seas,'' is
clear from this text in the Clean Water Act. First, Congress
established a broad definition of a term foundational to advancing the
Act's clear objective that requires additional interpretation to
implement that term by the expert agencies charged with administering
the statute. Second, Congress explicitly delegated such authority to
EPA: ``The Administrator is authorized to prescribe such regulations as
are necessary to carry out his functions under this Act.'' 33 U.S.C.
1361 (Clean Water Act section 501). Clearly, interpreting this key term
through regulation is necessary to carry out the functions of the Act.
    Congressional intent affirms this delegation. The breadth of the
definition of ``navigable waters'' reflects a deliberate choice by
Congress to both enact a statute with a broad scope of waters protected
by Federal law and to delegate the authority to interpret the
specialized term and its definition to the expert agencies. The
relevant House bill would have defined ``navigable waters'' as the
``navigable waters of the United States, including the territorial
seas.'' H.R. Rep. No. 911, 92d Cong., 2d Sess. 356 (1972) (emphasis
omitted). But the House was concerned that the definition might be
given an unduly narrow interpretation. The House Report observed: ``One
term that the Committee was reluctant to define was the term `navigable
waters.' The reluctance was based on the fear that any interpretation
would be read narrowly. However, this is not the Committee's intent.
The Committee fully intends that the term `navigable waters' be given
the broadest possible constitutional interpretation unencumbered by
agency determinations which have been made

or may be made for administrative purposes.'' H.R. Rep. No. 92-911, at
131 (1972). The Senate Report also expressed disapproval of the narrow
construction by the Corps of the scope of waters protected under prior
water protection statutes, stating ``[t]hrough a narrow interpretation
of the definition of interstate waters the implementation [of the] 1965
Act was severely limited. Water moves in hydrologic cycles and it is
essential that discharge of pollutants be controlled at the source.''
S. Rep. No. 92-414, at 77 (1971). Thus, in conference the word
``navigable'' was deleted from that definition, and the conference
report again urged that the term ``be given the broadest possible
constitutional interpretation unencumbered by agency determinations
which have been made or may be made for administrative purposes.'' S.
Conf. Rep. No. 1236, 92d Cong., 2d Sess. 144 (1972). Congress thus
intended the agencies to which it granted authority to implement the
Clean Water Act to interpret the scope of the definition of ``navigable
waters'' consistent with Congress's intent and objective in enacting
the Act.
    The Supreme Court has also affirmed the conclusion that it is the
agencies' role to interpret the term ``waters of the United States.''
As the Court explained in Riverside Bayview, Congress delegated a
``breadth of federal regulatory authority'' and expected the agencies
to tackle the ``inherent difficulties of defining precise bounds to
regulable waters.'' 474 U.S. at 134.
    In addition, any ambiguity in Congress's terms in Clean Water Act
section 502(7) further underscores the role of the agencies in
interpreting the statutory language. The Riverside Bayview Court
deferred to and upheld the agencies' interpretation of the Clean Water
Act to protect wetlands adjacent to navigable-in-fact bodies of water,
stating ``[a]n agency's construction of a statute it is charged with
enforcing is entitled to deference if it is reasonable and not in
conflict with the expressed intent of Congress.'' 474 U.S. at 131
(citations omitted). All nine Justices in Rapanos again recognized that
there was ambiguity in the terms of the Clean Water Act. 547 U.S. at
752, 758, 780, 796, 811-12. In concurring with the Rapanos plurality
opinion, the Chief Justice explained that, given the ``broad, somewhat
ambiguous, but nonetheless clearly limiting terms Congress employed in
the Clean Water Act, the Corps and the EPA would have enjoyed plenty of
room to operate'' if they had addressed the relevant interpretive
questions through rulemaking. 547 U.S. at 758 (Roberts, C.J.,
concurring). The Chief Justice emphasized the breadth of the agencies'
discretion in defining ``waters of the United States'' through
rulemaking; indeed, the agencies' interpretations under the Clean Water
Act, Chief Justice Roberts emphasized, are ``afforded generous leeway
by the courts.'' Id. at 758.
    In exercising their authority to interpret the statute in this
rule, the agencies are ``employing the traditional tools of statutory
interpretation,'' American Hospital Association v. Becerra, 142 S. Ct.
1896, 1906 (2022) (per curiam), beginning with ``the text and structure
of the statute,'' id. at 1904, as well as ``with reference to the
statutory context, `structure, history, and purpose,' '' Abramski v.
United States, 573 U.S. 169, 179 (2014) (citation omitted). As
discussed further in this section IV.A of the preamble, the agencies
have used additional tools of statutory construction, including the
statutory history, the statute as a whole, the objective of the Clean
Water Act, and the legislative history, which clears up ambiguity, in
construing the Act. See Bostock v. Clayton County, Georgia, 140 S. Ct.
1731, 1749 (2020) (discussing use of legislative history by the Supreme
Court ``when interpreting ambiguous statutory language'' (emphasis in
original) and noting that ``[l]egislative history, for those who take
it into account, is meant to clear up ambiguity, not create it''
(citing Milner v. Department of Navy, 562 U.S. 562, 574 (2011))).
    The agencies have also properly brought to bear their expertise and
experience in construing the Clean Water Act. As the Supreme Court
concluded in Riverside Bayview, ``In view of the breadth of federal
regulatory authority contemplated by the Act itself and the inherent
difficulties of defining precise bounds to regulable waters, the 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.'' 474 U.S. at
134. In addition, the agencies have more than 45 years of experience
implementing the longstanding pre-2015 regulations defining ``waters of
the United States,'' including more than a decade of implementing those
regulations consistent with the Supreme Court's decisions in Riverside
Bayview, SWANCC, and Rapanos, and have concluded this rule is also
consistent with the ``longstanding practice of [the agencies] in
implementing the relevant statutory authorities.'' Biden v. Missouri,
142 S. Ct. 647, 652 (2022). Finally, Congress is aware of the agencies'
longstanding interpretation of ``waters of the United States'' and has
not acted to limit the agencies' interpretation, but rather has
incorporated aspects of the agencies' regulatory definition into the
statute. See section IV.A.2.b of this preamble.
    Further, agencies have inherent authority to reconsider past
decisions and to revise, replace, or repeal a decision to the extent
permitted by law and supported by a reasoned explanation. FCC v. Fox
Television Stations, Inc., 556 U.S. 502, 515 (2009) (``Fox''); Motor
Vehicle Manufacturers Ass'n of the United States, Inc. v. State Farm
Mutual Automobile Insurance Co., 463 U.S. 29, 42 (1983) (``State
Farm''); see also Encino Motorcars, LLC v. Navarro, 136 S. Ct. 2117,
2125 (2016) (``Agencies are free to change their existing policies as
long as they provide a reasoned explanation for the change.''). Such a
decision need not be based upon a change of facts or circumstances. A
revised rulemaking based ``on a reevaluation of which policy would be
better in light of the facts'' is ``well within an agency's
discretion.'' Nat'l Ass'n of Home Builders v. EPA, 682 F.3d 1032, 1038
& 1043 (D.C. Cir. 2012) (citing Fox, 556 U.S. at 514-15). As discussed
further in section IV.B.3 of this preamble, the agencies have reviewed
the 2020 NWPR and determined that the rule should be replaced. This
rule properly considers the objective of the Clean Water Act, is
consistent with the text and structure of the Act, informed by relevant
Supreme Court precedent, and reflects the record before the agencies,
including consideration of the best available science, as well as the
agencies' expertise and experience implementing the pre-2015 regulatory
regime.
    To be clear, in this rule the agencies are exercising the authority
granted to them by Congress to construe and implement the Clean Water
Act and to interpret an ambiguous term and its statutory definition.
Therefore, while the agencies' interpretation of the statute is
informed by Supreme Court decisions, including Rapanos, it is not an
interpretation of the multiple opinions in Rapanos, nor is it based on
an application of the Supreme Court's principles to derive a governing
rule of law from a decision of the Court in a case such as Rapanos
where ``no opinion commands a majority.'' Rapanos, 547 U.S. at 758
(Roberts, C.J., concurring) (citing Marks v. United States, 430 U.S.
188, 193 (1977) (``Marks'')). Rather, this rule codifies the agencies'
interpretation of ``navigable waters'' informed by the text of the
relevant provisions of the Clean Water

Act and the statute as a whole, as well as the scientific record,
relevant Supreme Court case law, input from public comment, 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,'' including more than a decade of implementing
the regulations after Rapanos. Based on these considerations, the
agencies have concluded that the significant nexus standard in this
rule is the best interpretation of section 502(7) of the Clean Water
Act.
2. This Rule Advances the Objective of the Clean Water Act
    This rule is grounded in the Clean Water Act's objective ``to
restore and maintain the chemical, physical, and biological integrity
of the Nation's waters,'' 33 U.S.C. 1251(a). This rule advances the
Clean Water Act's objective by defining ``waters of the United States''
to include waters that significantly affect the chemical, physical, or
biological integrity of traditional navigable waters, the territorial
seas, and interstate waters; and waters that meet the relatively
permanent standard. The limitations in the definition ensure that the
agencies will not assert jurisdiction where the effect on traditional
navigable waters, the territorial seas, and interstate waters--i.e.,
the paragraph (a)(1) waters--is not significant. This rule is informed
by the best available science on the functions provided by upstream
waters, including wetlands, to restore and maintain the integrity of
paragraph (a)(1) waters because the rule recognizes that upstream
waters can have significant effects on such waters and enables the
agencies to make science-informed decisions about such effects. This
rule thus defines ``waters of the United States'' to include the
familiar types of waters in the 1986 regulations--traditional navigable
waters, interstate waters, impoundments, tributaries, the territorial
seas, adjacent wetlands, and waters that do not fall within the other
categories--while adding, where appropriate, a requirement that waters
also meet either the significant nexus standard or the relatively
permanent standard.
a. The Objective of the Clean Water Act To Protect Water Quality Must
Be Considered When Defining ``Waters of the United States''
    A statute must be interpreted in light of the purposes Congress
sought to achieve. See, e.g., Gen. Dynamics Land Sys., Inc. v. Cline,
540 U.S. 581 (2004). When considering the scope of the Clean Water Act,
the Supreme Court often begins with the objective of the Act and
examines the relevant question through that lens. Thus, the agencies
must consider the objective of the Clean Water Act in interpreting the
scope of the statutory term ``waters of the United States.'' Here,
Congress made its purpose crystal clear by stating its objective in the
first section of the statute. The objective of the Clean Water Act is
``to restore and maintain the chemical, physical, and biological
integrity of the Nation's waters.'' 33 U.S.C. 1251(a). To adequately
consider the Clean Water Act's statutory objective, a rule defining
``waters of the United States'' must consider its effects on the
chemical, physical, and biological integrity of the nation's waters.
And--as the text and structure of the Clean Water Act, supported by
legislative history and Supreme Court decisions, make clear--protecting
the chemical, physical, and biological integrity of the nation's waters
means protecting their water quality.
    The Clean Water Act begins with the objective in section 101(a) and
establishes numerous programs all designed to protect the integrity of
the nation's waters, ranging from permitting programs and enforcement
authorities, to water quality standards and effluent limitations
guidelines, to research and grant provisions. Section 102 of the Clean
Water Act requires the Administrator to, after consultation, develop
comprehensive programs for preventing, reducing, or eliminating the
pollution of the navigable waters.
    One of the Clean Water Act's principal tools in protecting the
integrity of the nation's waters is section 301(a), which generally
prohibits ``the discharge of any pollutant by any person'' without a
permit or other authorization under the Act. Other substantive
provisions of the Clean Water Act that use the term ``navigable
waters'' and are designed to meet the statutory objective include the
section 402 permit program, the section 404 dredged and fill permit
program, the section 311 oil spill prevention and response program, the
section 303 water quality standards and total maximum daily load
programs, and the section 401Tribal and State water quality
certification process. Each of these programs is designed to protect
water quality and, therefore, further the objective of the Clean Water
Act. The question of Federal jurisdiction is foundational to most
programs administered under the Clean Water Act. See section III.A.1 of
this preamble.\44\
---------------------------------------------------------------------------

    \44\ Additional provisions are also designed to achieve the
Clean Water Act's statutory objective and use its specific language,
including the definition of ``pollution,'' which the Act defines as
``the man-made or man-induced alteration of the chemical, physical,
biological, and radiological integrity of water.'' 33 U.S.C.
1362(19).
---------------------------------------------------------------------------

    Two recent Supreme Court Clean Water Act decisions, County of Maui,
Hawaii v. Hawaii Wildlife Fund, 140 S. Ct. 1462, 1476 (2020) (``Maui'')
and Nat'l Ass'n of Mfrs. v. Dep't of Defense, 138 S. Ct. 617, 624
(2018) (``National Association of Manufacturers''), affirm that
Congress used specific language in the definitions of the Clean Water
Act in order to meet the objective of the Act, that the definition of
``waters of the United States'' is fundamental to meeting the objective
of the Act, and, therefore, that the objective of the Act must be
considered in interpreting the term ``waters of the United States.''
    In Maui, the Supreme Court instructed that ``[t]he object in a
given scenario will be to advance, in a manner consistent with the
statute's language, the statutory purposes that Congress sought to
achieve.'' 140 S. Ct. at 1476. The Court, in recognizing that
Congress's purpose to `` `restore and maintain the . . . integrity of
the Nation's waters' '' is ``reflected in the language of the Clean
Water Act,'' also found that ``[t]he Act's provisions use specific
definitional language to achieve this result,'' noting that among that
definitional language is the phrase ``navigable waters.'' Id. at 1468-
69 (quoting 33 U.S.C. 1251(a)).\45\ Thus, in accordance with Maui, in
interpreting the ``specific definitional language'' of the Clean Water
Act, the agencies must ensure that they are advancing the statutory
purposes Congress sought to achieve.
---------------------------------------------------------------------------

    \45\ The Court explained:
    The Act's provisions use specific definitional language to
achieve this result. First, the Act defines ``pollutant'' broadly,
including in its definition, for example, any solid waste,
incinerator residue, `` `heat,' '' `` `discarded equipment,' '' or
sand (among many other things). Sec.  502(6), 86 Stat. 886. Second,
the Act defines a ``point source'' as `` `any discernible, confined
and discrete conveyance . . . from which pollutants are or may be
discharged,' '' including, for example, any `` `container,' '' ``
`pipe, ditch, channel, tunnel, conduit,' '' or `` `well.' '' Sec.
502(14), id., at 887. Third, it defines the term `` `discharge of a
pollutant' '' as `` `any addition of any pollutant to navigable
waters [including navigable streams, rivers, the ocean, or coastal
waters] from any point source.' '' Sec.  502(12), id., at 886.
    Maui, 140 S. Ct. at 1469.
---------------------------------------------------------------------------

    In National Association of Manufacturers, the Court confirmed the
importance of considering the plain language of the objective of the
Clean Water Act when interpreting the

specific definitional language of the Act, and in particular when
interpreting the definitional language ``waters of the United States.''
The Court identified section 301's prohibition on unauthorized
discharges as one of the Clean Water Act's principal tools for
achieving the objective and then identified the definition of ``waters
of the United States'' as key to the scope of the Act: ``Congress
enacted the Clean Water Act in 1972 `to restore and maintain the
chemical, physical, and biological integrity of the Nation's waters.'
[33 U.S.C.] 1251(a). One of the Act's principal tools in achieving that
objective is [section] 1311(a), which prohibits `the discharge of any
pollutant by any person,' except in express circumstances. . . .
Because many of the Clean Water Act's substantive provisions apply to
`navigable waters,' the statutory phrase `waters of the United States'
circumscribes the geographic scope of the Act in certain respects.''
138 S. Ct. 617, 624. Thus, consideration of the objective of the Clean
Water Act is of particular importance when defining the foundational
phrase ``waters of the United States.''
    Many other Supreme Court decisions confirm the importance of
considering the Clean Water Act's objective. When faced with questions
of statutory interpretation on the scope of the Clean Water Act, many
Supreme Court decisions begin with the objective of the Act and examine
the relevant question through that lens. See, e.g., PUD No. 1 of
Jefferson Cty v. Washington Dep't of Ecology, 511 U.S. 700, 704 (1994)
(interpreting the scope of Clean Water Act section 401 and finding that
the Act ``is a comprehensive water quality statute designed to `restore
and maintain the chemical, physical, and biological integrity of the
Nation's waters,' '' that ``[t]he Act also seeks to attain `water
quality which provides for the protection and propagation of fish,
shellfish, and wildlife,' '' and that ``[t]o achieve these ambitious
goals, the Clean Water Act establishes distinct roles for the Federal
and State Governments''); EPA v. California ex rel. State Water
Resources Control Bd., 426 U.S. 200, 203, 205 n.12 (1976) (``In 1972,
prompted by the conclusion of the Senate Committee on Public Works that
`the Federal water pollution control program . . . has been inadequate
in every vital aspect,' Congress enacted the [Clean Water Act],
declaring `the national goal that the discharge of pollutants into the
navigable waters be Eliminated by 1985.'''); Arkansas v. Oklahoma, 503
U.S. 91, 101 (1992) (reviewing the scope of EPA's authority to issue a
permit affecting a downstream State and finding that the Clean Water
Act ``anticipates a partnership between the States and the Federal
Government, animated by a shared objective: `to restore and maintain
the chemical, physical, and biological integrity of the Nation's
waters' ''); S.D. Warren Co. v. Maine Bd. of Envtl. Protection, 126 S.
Ct. 1843, 1852-53 (2006) (interpreting the scope of ``discharge'')
(``Congress passed the Clean Water Act to `restore and maintain the
chemical, physical, and biological integrity of the Nation's waters,'
33 U.S.C. [section] 1251(a) . . . .''); Int'l Paper Co. v. Ouellette,
479 U.S. 481, 492-93 (1987) (``Congress intended the 1972 Act
amendments to `establish an all-encompassing program of water pollution
regulation.' . . . The Act applies to all point sources and virtually
all bodies of water, and it sets forth the procedures for obtaining a
permit in great detail. . . . Given that the Act itself does not speak
directly to the issue, the Court must be guided by the goals and
policies of the Act in determining whether it in fact pre-empts an
action based on the law of an affected State.'').
    Along with Maui and National Association of Manufacturers, these
cases confirm that, for purposes of a rulemaking revising the
definition of ``waters of the United States,'' the agencies must
consider the rule's effect on the chemical, physical, and biological
integrity of the nation's waters--i.e., on the quality of those waters.
The Supreme Court in Riverside Bayview explained the inherent link
between the Clean Water Act's objective and water quality: ``This
objective incorporated a broad, systemic view of the goal of
maintaining and improving water quality: as the House Report on the
legislation put it, `the word ``integrity'' . . . refers to a condition
in which the natural structure and function of ecosystems [are]
maintained.' '' 474 U.S. at 132 (citations omitted).
    The statutory structure further confirms that ``waters of the
United States'' must be interpreted to account for the Clean Water
Act's broader objective of promoting water quality. The Act is replete
with 90 references to water quality--from the goals set forth to meet
the statutory objective to the provisions surrounding research,
effluent limitations, and water quality standards. See, e.g., 33 U.S.C.
1251(a)(2) (``[I]t is the national goal that wherever attainable, an
interim goal of water quality which provides for the protection and
propagation of fish, shellfish, and wildlife and provides for
recreation in and on the water be achieved. . . .''), 1254(b)(6)
(providing that the Administrator shall collect ``basic data on
chemical, physical, and biological effects of varying water quality''),
1311(b)(1)(C) (requiring permits to have limits as stringent as
necessary to meet water quality standards), 1313(c) (providing that
water quality standards ``shall be such as to protect the public health
or welfare, enhance the quality of water and serve the purposes of this
[Act]''). And Congress was clear that ``[t]he development of
information which describes the relationship of pollutants to water
quality is essential for carrying out the objective of the Act.'' S.
Rep. No. 92-414 at 47 (1972), as reprinted in 1972 U.S.C.C.A.N. 3668,
3716; see also id. at 3717 (``Water quality is intended to refer to the
biological, chemical and physical parameters of aquatic ecosystems, and
is intended to include reference to key species, natural temperature
and current flow patterns, and other characteristics which help
describe ecosystem integrity. . . . The criteria will allow the
translation of the narrative of the general objective of the Act to
specific and precise parameters.''); id. at 3742 (``The Committee has
added a definition of pollution to further refine the concept of water
quality measured by the natural chemical, physical and biological
integrity.''). As the Sixth Circuit explained shortly after the 1972
enactment of the Clean Water Act: ``It would, of course, make a mockery
of [Congress's] powers if its authority to control pollution was
limited to the bed of the navigable stream itself. The tributaries
which join to form the river could then be used as open sewers as far
as federal regulation was concerned. The navigable part of the river
could become a mere conduit for upstream waste.'' United States v.
Ashland Oil & Transp. Co., 504 F.2d 1317, 1326 (6th Cir. 1974).
    To be clear, the objective of the Clean Water Act is not the only
factor relevant to determining the scope of the Act. Rather, in light
of the precise language of the definitions in the Act, the importance
of water quality to the statute as a whole, and Supreme Court decisions
affirming that consideration of the objective of the Act is of primary
importance in defining its scope, the agencies conclude that a rule
defining ``waters of the United States'' must substantively consider
the effects of a revised definition on the integrity of the nation's
waters and advance the protection of the quality of those waters. As
discussed further below, this rule

properly considers and advances the objective of the Clean Water Act
because the science conclusively demonstrates that upstream waters,
including wetlands, can affect the quality of downstream waters and
ensures application of Clean Water Act water quality programs to
upstream waters when their effect on downstream traditional navigable
waters, territorial seas, and interstate waters is significant.
b. This Rule Is Founded on the 1986 Regulations, Which Advance the
Objective of the Clean Water Act
    The 1986 regulations--which are substantially the same as the 1977
regulations--represented the agencies' interpretation of the Clean
Water Act in light of its objective and their scientific knowledge
about aquatic ecosystems. In this rule, the agencies are exercising
their authority to construe ``waters of the United States'' to mean the
waters defined by the familiar 1986 regulations, with amendments to
reflect the agencies' construction of limitations on the scope of
``waters of the United States,'' based on the law, the science, and
agency expertise. Of particular import, the agencies are limiting the
scope of the longstanding regulatory categories by adding a requirement
that tributaries, adjacent wetlands (that are adjacent to waters other
than paragraph (a)(1) waters), and lakes and ponds, streams, and
wetlands that are not identified in paragraphs (a)(1) through (4) meet
either the relatively permanent standard or the significant nexus
standard as established in this rule. The agencies also considered the
extensive public comment on the proposed rule in developing this final
rule.
    The best available science confirms that the 1986 regulations
remain a reasonable foundation for a definition of ``waters of the
United States'' that furthers the water quality objective of the Clean
Water Act. See Technical Support Document. This section of the preamble
describes the agencies' historic rationale for the 1986 regulation and
its regulatory categories and describes the latest science that
supports the conclusion that the categories of waters identified in the
1986 regulations provide functions that restore and maintain the
chemical, physical, and biological integrity of traditional navigable
waters, the territorial seas, and interstate waters.
    The agencies' historic regulations, eventually promulgated and
referred to as the 1986 regulations, were based on the agencies'
construction of the scope of the Clean Water Act and their scientific
and technical judgment about which waters needed to be protected to
restore and maintain the chemical, physical, and biological integrity
of traditional navigable waters, the territorial seas, and interstate
waters (i.e., the paragraph (a)(1) waters). For more than 45 years, the
agencies recognized the need to protect ``the many tributary streams
that feed into the tidal and commercially navigable waters . . . since
the destruction and/or degradation of the physical, chemical, and
biological integrity of each of these waters is threatened by the
unregulated discharge of dredged or fill material.'' See, e.g., 42 FR
37122, 37123 (July 19, 1977). The agencies have also long recognized
that the nation's wetlands are ``a unique, valuable, irreplaceable
water resource. . . . Such areas moderate extremes in waterflow, aid in
the natural purification of water, and maintain and recharge the ground
water resource.'' EPA, Protection of Nation's Wetlands: Policy
Statement, 38 FR 10834 (May 2, 1973). In Riverside Bayview, the Supreme
Court acknowledged that the agencies were interpreting the Clean Water
Act consistent with its objective and based on their scientific
expertise:

    In view of the breadth of federal regulatory authority
contemplated by the Act itself and the inherent difficulties of
defining precise bounds to regulable waters, the 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.

474 U.S. at 134.
    And, as the Corps stated in promulgating the 1977 definition,
``[t]he regulation of activities that cause water pollution cannot rely
on . . . artificial lines, however, but must focus on all waters that
together form the entire aquatic system. Water moves in hydrologic
cycles, and the pollution of . . . part of the aquatic system . . .
will affect the water quality of the other waters within that aquatic
system.'' 42 FR 37128 (July 19, 1977).
    Thus, this rule includes the categories long identified by the
agencies as affecting the water quality of paragraph (a)(1) waters,
including tributaries, adjacent wetlands, impoundments, and waters that
do not fall within any of the more specific categories of the
definition (a category that has been modified and codified in this rule
as paragraph (a)(5) waters).
    As discussed below, however, while these longstanding categories
continue to provide a reasonable foundation for this rule, this rule
codifies limitations on these categories based on the agencies'
interpretation of the Clean Water Act. To be clear, this rule does not
automatically include all tributaries, adjacent wetlands, and waters
assessed under paragraph (a)(5) as jurisdictional waters. Rather, the
agencies conclude that utilizing these longstanding, familiar
categories of waters, subject to the relatively permanent or
significant nexus jurisdictional standards, is consistent with the best
available science because the significant nexus standard established in
this rule is based on an assessment of the effects of waters in these
categories on the water quality of paragraph (a)(1) waters. In
addition, the agencies believe that waters that meet the relatively
permanent standard individually and cumulatively provide many functions
that benefit the integrity of paragraph (a)(1) waters. See section
IV.A.3.a.ii of this preamble. This rule does categorically include
wetlands adjacent to paragraph (a)(1) waters. Riverside Bayview, 474
U.S. at 135; see also 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. That is the holding of Riverside Bayview.'').
This rule enables the agencies to make science-informed determinations
of whether or not a water that falls within these categories meets
either jurisdictional standard and therefore satisfies the definition
of ``waters of the United States'' on a case-specific basis. For a
detailed discussion of implementation of adjacent wetlands under this
rule, see section IV.A.4 of this preamble; for additional guidance to
landowners on jurisdictional determinations, see section IV.C.10 of
this preamble.
i. The Agencies' Longstanding Interpretation That Tributaries Can Be
``Waters of the United States'' Is a Reasonable Foundation for This
Rule
    The agencies have long construed the Clean Water Act to include
tributaries as ``waters of the United States.'' In 1973, EPA's General
Counsel issued an opinion upon which the agency's subsequent rulemaking
was based that tributaries were included within the term ``navigable
waters,'' finding that ``this broad interpretation is well grounded in
the language of the statute and in the legislative history, and
comports with the expressed intent of Congress to `restore and maintain
the chemical, physical, and biological integrity of the Nation's
waters.' '' Envtl.

Prot. Agency, Off. Gen. Counsel, Meaning of the Term ``Navigable
Waters'' (February 13, 1973), 1973 WL 21937. The Corps explained in
1977 that its regulations necessarily encompassed ``the many tributary
streams that feed into the tidal and commercially navigable waters''
because ``the destruction and/or degradation of the physical, chemical,
and biological integrity of each of these waters is threatened by the
unregulated discharge of dredged or fill material.'' 42 FR 37123 (July
19, 1977).
    The conclusion that the Clean Water Act includes tributaries is
consistent with the structure and history of the statute. The Clean
Water Act was not ``merely another law `touching interstate waters,' ''
but rather ``a `total restructuring' and `complete rewriting' of [then]
existing water pollution legislation.'' City of Milwaukee v. Illinois,
451 U.S. 304, 317 (1981) (citations omitted). Congress concluded that
prior measures had been ``inadequate in every vital aspect,'' and it
enacted a wholly new scheme of point-source-based pollution controls.
EPA v. California ex rel. State Water Res. Control Bd., 426 U.S. 200,
203 (1976) (citation omitted). The Clean Water Act thus reflected
Congress's fundamental dissatisfaction with prior law.
    Even before it enacted the 1972 Clean Water Act amendments,
Congress had recognized, and had acted to address, the danger that
pollution of tributaries may impair the quality of traditional
navigable waters downstream. Prior to those amendments, the Federal
Water Pollution Control Act established procedures for abatement of
``(t)he pollution of interstate or navigable waters in or adjacent to
any State or States (whether the matter causing or contributing to such
pollution is discharged directly into such waters or reaches such
waters after discharge into a tributary of such waters).'' 33 U.S.C.
1160(a) (1970) (emphasis added). Under specified circumstances, the
Attorney General was authorized to bring suit on behalf of the United
States ``to secure abatement of the pollution.'' 33 U.S.C. 1160(g)
(1970). Indeed, the regulation of tributaries as part and parcel of a
Federal effort to protect traditional navigable waters has been a
feature of Federal law for over 100 years. Since its enactment as
section 13 of the Rivers and Harbors Appropriation Act of 1899 (RHA),
Ch. 425, section 13, 30 stat. 1152, the Refuse Act of 1899 has
prohibited the discharge of refuse material into any ``navigable water
of the United States or into any tributary of any navigable water of
the United States,'' as well as depositing refuse material ``on the
bank of any navigable water, or on the bank of any tributary of any
navigable water.'' 33 U.S.C. 407. That provision does not limit the
covered ``tributar[ies]'' to those that are themselves used or
susceptible to use for navigation.
    Thus, well over a hundred years ago, Congress understood the
necessity of protecting tributaries in order to protect traditional
navigable waters and recognized its authority over those tributaries,
and in the Clean Water Act Congress sought to expand protection of the
nation's waters. It would therefore be unreasonable for the agencies to
construe the Clean Water Act, with its comprehensive focus on limiting
discharges of pollutants to ``waters of the United States'' and
restoring and maintaining the chemical, physical, and biological
integrity of the nation's waters, to exclude tributaries to traditional
navigable waters, the territorial seas, and interstate waters.
    Section 404(g) of the Clean Water Act further supports the
agencies' interpretation that the Act covers such tributaries. Section
404(g) authorizes States to administer their own permit programs over
certain waters. Section 404(g)(1) provides, in relevant part, that any
State ``desiring to administer its own individual and general permit
program for the discharge of dredged or fill material into the
navigable waters (other than those waters which are presently used, or
are susceptible to use in their natural condition or by reasonable
improvement as a means to transport interstate or foreign commerce . .
. including wetlands adjacent thereto)'' may submit a description of
this proposed program to EPA. 33 U.S.C. 1344(g)(1).\46\ Section
404(g)(1)'s reference to navigable waters ``other than those waters
used or susceptible to use'' for transporting commerce and their
adjacent wetlands plainly indicates that the Clean Water Act covers
more than the waters in this parenthetical.
---------------------------------------------------------------------------

    \46\ The Corps retains permitting authority over the ``waters of
the United States'' that States cannot or do not assume.
---------------------------------------------------------------------------

    The Supreme Court has also recognized the relevance of section
404(g) to interpreting the scope of Clean Water Act jurisdiction. In
Riverside Bayview, while the Supreme Court stated that section 404(g)
``does not conclusively determine the construction to be placed on the
use of the term `waters' elsewhere in the Act,'' the Court went on to
say with respect to the significance of section 404(g) that ``the
various provisions of the Act should be read in pari materia [i.e.,
construed together],'' ultimately concluding that section 404(g)
``suggest[s] strongly that the term `waters' as used in the Act''
supports the Corps' interpretation of ``waters of the United States''
to include wetlands. 474 U.S. at 138 n.11 (emphasis added). While the
Court in SWANCC did not read section 404(g) to definitively answer the
question of the scope of ``waters of the United States,'' the Court
offered a hypothesis that ``Congress simply wanted to include all
waters adjacent to `navigable waters,' such as non-navigable
tributaries and streams.'' 531 U.S. at 171. And all members of the
Supreme Court agreed with the observation of the Rapanos plurality that
the 1977 Clean Water Act's authorization for States to administer the
section 404 program for ``navigable waters . . . other than'' those
used or suitable for use ``to transport interstate or foreign
commerce,'' 547 U.S. at 731 (quoting 33 U.S.C. 1344(g)(1)), ``shows
that the Act's term `navigable waters' includes something more than
traditional navigable waters.'' Id. In light of the history of the Act
as well as Congress's clear understanding of the relationship between
tributaries and traditional navigable waters, tributaries--whether or
not they themselves are traditional navigable waters--are an obvious
candidate for the Clean Water Act's broader coverage. As noted above,
even long before 1972, Congress had addressed the danger that pollution
of tributaries may impair the quality of traditional navigable waters
downstream, and it is implausible to suppose that Congress's landmark
1972 legislation actually reduced the scope of the prior statutes.
    Construing ``waters of the United States'' to include tributaries
of traditional navigable waters, the territorial seas, interstate
waters, or impoundments of ``waters of the United States'' is also
consistent with the discussion of tributaries in the Clean Water Act's
legislative history. The Senate Report accompanying the 1972 Act states
that ``navigable waters'' means ``the navigable waters of the United
States, portions thereof, tributaries thereof, and includes the
territorial seas and the Great Lakes.'' S. Rep. No. 92-414, at 77
(1971), as reprinted in 1972 U.S.C.C.A.N. 3668, 3742 (emphasis added).
Congress thus restated that ``reference to the control requirements
must be made to the navigable waters, portions thereof, and their
tributaries.'' Id. at 3743 (emphasis added).
    In addition, this rule and the 1986 regulations construe the
statute not to

distinguish between human-made or human-altered tributaries and natural
tributaries. This construction is consistent with the text of the
statute and science. Most obviously, such a distinction would render
superfluous section 404's exception for ``the discharge of dredged or
fill material . . . for the . . . maintenance of drainage ditches,''
section 404(f)(1)(C), because if human-made or human-altered
tributaries were not included, drainage ditches would not be covered in
the first place. More broadly, many of the nation's urban waterways are
channelized, and the Clean Water Act has long been understood to
encompass ``natural, modified, or constructed'' tributaries of other
covered waters. 80 FR 37078 (June 29, 2015). For example, many of the
streams in Houston, Texas, have been channelized, culverted, or
otherwise altered over time, in part for flood control purposes, and
the Clean Water Act protects many of these human-modified streams.
Removing the Clean Water Act's protections for these tributaries could
increase contributions of nutrients, sediment, and other pollutants
downstream to paragraph (a)(1) waters, such as the Trinity River. Such
an approach would also affect millions of miles of other such
tributaries, undermining the integrity of paragraph (a)(1) waters
throughout the country.
    Moreover, the Clean Water Act's specialized definition of
``navigable waters'' does not turn on any such distinctions between
natural and human-made or -altered tributaries, which have no bearing
on a tributary's capacity to carry water (and pollutants) to
traditional navigable waters, the territorial seas, or interstate
waters. See, e.g., Technical Support Document section III.A.iv
(explaining that manmade ditches ``perform many of the same functions
as natural tributaries,'' including ``convey[ing] water that carries
nutrients, pollutants, and other constituents, both good and bad, to
downstream traditional navigable waters, the territorial seas, and
interstate waters''). Such a distinction would also be inconsistent
with Rapanos. That decision addressed consolidated cases involving
wetlands connected to traditional navigable waters by ``ditches or man-
made drains.'' Rapanos, 547 U.S. at 729 (plurality opinion). The
Rapanos plurality concluded that the cases should be remanded for the
lower courts to determine whether the channels at issue satisfied the
plurality's jurisdictional standard, and those further lower-court
proceedings would have been superfluous if the manmade character of the
ditches and drains had precluded their coverage as ``waters of the
United States.''
    As discussed below and further in section III.A of the Technical
Support Document, the best available science supports the 1986
regulations' conclusions, and the agencies' construction of the Clean
Water Act in this rule, about the importance of tributaries to the
water quality of downstream paragraph (a)(1) waters: tributaries
provide natural flood control, help sustain flow downstream, recharge
groundwater, trap sediment, store and transform pollutants, decrease
high levels of chemical contaminants, recycle nutrients, create and
maintain biological diversity, and sustain the biological productivity
of downstream rivers, lakes, and estuaries.
ii. The Agencies' Longstanding Interpretation of Adjacent Wetlands as
``Waters of the United States'' Is a Reasonable Foundation for This
Rule
    For more than four decades, the agencies have construed the
``waters of the United States'' to include wetlands adjacent to other
jurisdictional waters. Wetlands, such as swamps, bogs, marshes, and
fens, are ``transitional areas between terrestrial and aquatic
ecosystems'' characterized by sustained inundation or saturation with
water. Science Report at 2-5. Wetlands play a critical role in
regulating water quality. Among other things, they provide flood
control and trap and filter sediment and other pollutants that would
otherwise be carried to downstream waters. See National Research
Council, Wetlands: Characteristics and Boundaries 35, 38 (1995) (NRC
Report, available at https://nap.nationalacademies.org/catalog/4766/wetlands-characteristics-and-boundaries; Technical Support Document
section III.B.
    The Corps published regulations to implement the section 404
permitting program in 1974. 39 FR 12115 (April 3, 1974). At that time,
the Corps took the view that for purposes of section 404 ``navigable
waters'' was an established term of art for waters that are subject to
Congress's power to regulate interstate channels of commerce, and that
the term should be given that meaning in the Clean Water Act--
notwithstanding the specialized definition of ``navigable waters'' in
the Act. Id. The Corps therefore asserted jurisdiction under section
404 only over the waters subject to section 10 of the Rivers and
Harbors Act of 1899. Id. at 12119.
    Reviewing courts, members of Congress, and EPA disagreed with the
Corps' initial approach. See, e.g., United States v. Ashland Oil &
Transp. Co., 504 F.2d 1317, 1325 (6th Cir. 1974); H.R. Rep. No. 1396,
93d Cong., 2d Sess. 23-27 (1974). In fact, EPA had previously
promulgated a rule defining ``waters of the United States'' far more
broadly than the Corps' regulations. 38 FR 13528 (May 22, 1973).
Ultimately, the Corps was ordered to adopt new regulations recognizing
the agency's ``full regulatory mandate.'' NRDC, Inc. v. Callaway, 392
F. Supp. 685, 686 (D.D.C. 1975).
    The Corps responded by broadening its definition of ``navigable
waters'' in a phased approach under which all of the waters in the
final regulation were ``waters of the United States,'' but the Corps
would begin regulating activities within each type of ``waters of the
United States'' in phases: Phase I, which was effective immediately,
covered ``coastal waters and coastal wetlands contiguous or adjacent
thereto or into inland navigable waters of the United States [a term
for waters protected under the Rivers and Harbors Act] and freshwater
wetlands contiguous or adjacent thereto''; Phase II, effective after
July 1, 1976, covered ``primary tributaries, freshwater wetlands
contiguous or adjacent to primary tributaries, and lakes''; and Phase
III, effective after July 1, 1977, covered ``discharges . . . into any
navigable water'' including intrastate lakes and rivers and their
adjacent wetlands. 40 FR 31320, 31324, 31326 (July 25, 1975). The Corps
defined ``adjacent'' to mean ``bordering, contiguous, or neighboring,''
and specified that ``[w]etlands 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.' '' 42 FR 37122, 37144 (July
19, 1977). The regulations also defined ``wetlands'' to mean ``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.'' Id. The agencies have thus
interpreted the term ``waters of the United States'' to include
wetlands since at least 1975.\47\
---------------------------------------------------------------------------

    \47\ The agencies' interpretation of ``waters of the United
States'' as including wetlands is consistent not only with the
history and text of Clean Water Act section 404(g), but also with
other parts of the statute and of the United States Code. For
example, in the Lake Champlain Basin Program, Congress referred to
``streams, rivers, lakes, and other bodies of water, including
wetlands.'' 33 U.S.C. 1270(g)(2) (emphasis added). Congress has also
referred to ``streams, rivers, wetlands, other waterbodies, and
riparian areas,'' 33 U.S.C. 2336(b)(2) (emphasis added), and defined
``coastal waters'' to mean the waters of the Great Lakes
``including'' portions of other ``bodies of water'' with certain
features, ``including wetlands,'' id. at 2802(5).

---------------------------------------------------------------------------

    Reacting to the Corps' broadened definition, leading up to the 1977
Amendments, Congress considered proposals to limit the geographic reach
of section 404. ``In both Chambers, debate on the proposals to narrow
the definition of navigable waters centered largely on the issue of
wetlands preservation.'' SWANCC, 531 U.S. at 170. A version of that
legislation, passed by the House, would have redefined ``navigable
waters'' for purposes of section 404 to mean a limited set of
traditional navigable waters and their adjacent wetlands. H.R. 3199,
95th Cong. section 16 (1977). But many legislators objected to the
proposed changes. When Congress rejected the attempt to limit the
geographic reach of section 404, it was well aware of the
jurisdictional scope of EPA and the Corps' definition of ``waters of
---------------------------------------------------------------------------
the United States.'' For example, Senator Baker stated:

    Interim final regulations were promulgated by the [C]orps [on]
July 25, 1975. . . . Together the regulations and [EPA] guidelines
established a management program that focused the decision-making
process on significant threats to aquatic areas while avoiding
unnecessary regulation of minor activities. On July 19, 1977, the
[C]orps revised its regulations to further streamline the program
and correct several misunderstandings. . . .
    Continuation of the comprehensive coverage of this program is
essential for the protection of the aquatic environment. The once
seemingly separable types of aquatic systems are, we now know,
interrelated and interdependent. We cannot expect to preserve the
remaining qualities of our water resources without providing
appropriate protection for the entire resource.
    Earlier jurisdictional approaches under the [Rivers and Harbors
Act] established artificial and often arbitrary boundaries . . . .

123 Cong. Rec. 26,725 (1977). Legislators were concerned the proposed
changes were an ``open invitation'' to pollute waters. Id. (remarks of
Sen. Hart); see also, e.g., id. at 26,714-26,716. The proposal was
ultimately voted down on the Senate floor. Id. at 26,728; cf. S. Rep.
No. 370, 95th Cong., 1st Sess. 10 (1977) (hereinafter, ``1977 Senate
Report''); Riverside Bayview, 474 U.S. at 136-137 (noting that
``efforts to narrow the definition of `waters' were abandoned; the
legislation as ultimately passed, in the words of Senator Baker,
`[retained] the comprehensive jurisdiction over the Nation's waters''
(citation omitted)). Federal preservation of wetlands was at the heart
of the debate over passage of the 1977 Act, with good reason. See 1977
Senate Report at 10 (``There is no question that the systematic
destruction of the Nation's wetlands is causing serious, permanent
ecological damage. The wetlands and bays, estuaries and deltas are the
Nation's most biologically active areas. They represent a principal
source of food supply. They are the spawning grounds for much of the
fish and shellfish which populate the oceans, and they are passages for
numerous [ ] game fish. They also provide nesting areas for a myriad of
species of bird and wildlife. The unregulated destruction of these
areas is a matter which needs to be corrected and which implementation
of section 404 has attempted to achieve.''). Earlier Federal and State
policy that encouraged filling wetlands had led to destruction of
roughly 117 million acres of wetlands in the contiguous United States,
or more than half the original total. See T.E. Dahl & Gregory J.
Allord, ``History of Wetlands in the Conterminous United States,'' in
National Water Summary on Wetland Resources at 19 (1996, available at
https://pubs.usgs.gov/wsp/2425/report.pdf).
    Congress instead modified the Clean Water Act in other ways to
respond to concerns about the scope of Federal authorities. Congress
exempted certain agricultural and silvicultural activities from the
section 404 permitting program. See 1977 Act section 67(b), 91 Stat.
1600 (33 U.S.C. 1344(f)(1)(A)). In addition, Congress authorized the
Corps to issue general permits to streamline the permitting process.
Id. (33 U.S.C. 1344(e)(1)). And importantly for understanding the scope
of ``waters of the United States,'' Congress modified section 404 in a
way that incorporated into the statutory text an explicit endorsement
of the Corps' regulation defining ``waters of the United States,''
including its inclusion of adjacent wetlands. Specifically, the 1977
Act section 67(b), 91 Stat. 1601, establishing section 404(g), allowed
Tribes and States to assume responsibility for the issuance of section
404 permits. As Congress explained in the legislative history, under
section 404(g) States could administer a permitting program for the
discharge of dredged or fill material into ``phase II and III waters''
following EPA approval, but the Corps would retain jurisdiction over
``those waters defined as the phase I waters in the Corps . . . 1975
regulations, with the exception of waters considered navigable solely
because of historical use.'' 123 Cong. Rec. 38,969 (December 15, 1977);
H.R. Conf. Rep. No. 830, 95th Cong., 1st Sess. 101 (1977), reprinted in
3 Legis. History 1977, at 185, 285. Accordingly, through section
404(g), Congress demonstrated its understanding of the Corps'
regulations and endorsed the scope of their coverage--allowing States
to assume authority to administer the Clean Water Act as it pertained
to the waters contained in phase II and III of the Corps' regulations
(Phase II, effective after July 1, 1976, covered ``primary tributaries,
freshwater wetlands contiguous or adjacent to primary tributaries, and
lakes'' and Phase III, effective after July 1, 1977, covered
``discharges . . . into any navigable water'' including intrastate
lakes and rivers and their adjacent wetlands. 40 FR 31320, 31324, 31326
(July 25, 1975)), and reserving for the Corps alone authority over the
waters contained in phase I of the Corps' regulations.
    With respect specifically to the inclusion of adjacent wetlands,
Congress was explicit in the text of the Clean Water Act. The text of
section 404(g) authorizes States and Tribes to administer the section
404 permitting program covering ``the discharge of dredged or fill
material into the navigable waters (other than those waters which are
presently used, or are susceptible to use in their natural condition or
by reasonable improvement as a means to transport interstate or foreign
commerce . . . including wetlands adjacent thereto).'' 33 U.S.C.
1344(g)(1) (emphasis added); see 33 U.S.C. 1377(e) (extension to
Tribes). The italicized reservation of authority to the Corps in
section 404(g) presupposed that ``wetlands adjacent'' to a subset of
traditional navigable waters were subject to the section 404 program,
since otherwise the exclusion of those wetlands from the Tribes' and
States' potential permitting authority would have been superfluous.
Other language in the 1977 legislative record confirms that
understanding. See 1977 Senate Report 10 (stating that committee wished
to ``maintain[ ]'' coverage of wetlands); H.R. Conf. Rep. No. 830, 95th
Cong., 1st Sess. 98, 104 (1977) (stating that the Corps will
``continue'' to exercise section 404 jurisdiction over ``adjacent
wetlands'').
    Moreover, with respect to which wetlands are adjacent, by using the
pre-existing term ``adjacent'' wetlands from the Corps' 1977
regulations, Congress signaled its intent to incorporate the Corps'
regulatory conception of adjacency. ``When a statutory term is
`obviously transplanted from another legal source,' it `brings the old
soil with it.' '' Taggart v. Lorenzen, 139 S. Ct. 1795, 1801 (2019)
(citation omitted). Here, that soil includes the full breadth of the
agencies' definition of ``adjacent'': bordering, contiguous, or
neighboring, as well as wetlands behind a berm or

barrier. That definition accords with the term's plain meaning.
Contemporaneous dictionaries defined the term ``adjacent'' in ways that
do not require direct abutment. See Black's Law Dictionary at 62 (rev.
4th ed. 1968) (``Lying near or close to; sometimes, contiguous;
neighboring. Adjacent implies that the two objects are not widely
separated, though they may not actually touch[.]'' (capitalization
altered; citation and emphasis omitted)); The American Heritage
Dictionary of the English Language at 16 (1975) (``Close to; next to;
lying near; adjoining.''); Webster's New International Dictionary of
the English Language at 32 (2d ed. 1958) (``Lying near, close, or
contiguous; neighboring; bordering on.'' (emphasis omitted)).
    Congress has on a number of additional occasions responded to
concerns about the breadth of the scope of Federal authorities not by
narrowing the scope of ``waters of the United States,'' but by
excluding particular types and sources of discharges of pollutants from
the NPDES program or from Clean Water Act jurisdiction altogether. For
example, the 1987 Water Quality Act (WQA) added section 402(l)(2) to
the Clean Water Act. This new section prohibits EPA and the states from
requiring NPDES permits for uncontaminated stormwater discharges from
oil and gas exploration, production, processing or treatment
operations, or transmission facilities. Later, section 323 of the
Energy Policy Act of 2005 added a new provision to Clean Water Act
section 502 defining the term ``oil and gas exploration, production,
processing, or treatment operations or transmission facilities.'' The
1987 WQA also enacted a new section 402(p) of the Act that established
a comprehensive new program for stormwater regulation. In that section,
Congress made clear that only some stormwater point source discharges
need NPDES permit coverage--those from industrial activity, from large
and medium municipalities, and that EPA or a State designates by
rulemaking or adjudication to protect water quality or because the
discharges contribute to violations of water quality standards or are
significant contributors of pollutants. Congress has also taken
numerous actions to amend the Clean Water Act to address discharges
from vessels. The 1972 version of the Act excluded ``sewage from
vessels'' from the definition of ``pollutant'' thus exempting it from
the permitting regime in favor of regulatory standards of performance.
See 33 U.S.C. 1322(b), 1362(6). In 1996, Congress similarly excluded
most discharges from vessels of the Armed Forces and tasked EPA and the
Department of Defense to jointly promulgate uniform national discharge
standards instead. See 33 U.S.C. 1322(n), 1362(6). In 2008, Congress
passed the Clean Boating Act, which exempted discharges incidental to
the normal operation of recreational vessels of all sizes from Clean
Water Act permitting requirements, in favor of EPA regulations. See 33
U.S.C. 1322(o)(1)(B); see also 33 U.S.C. 1342(r). And in 2018, Congress
enacted the Vessel Incidental Discharge Act which exempted from NPDES
routine discharges from many other types of vessels including small
vessels, fishing vessels, and commercial vessels larger than 79 feet.
See 33 U.S.C. 1322(p)(9)(C)(ii).
    Case law also supports the agencies' construction of the Clean
Water Act to cover adjacent wetlands as defined by the agencies. In
Riverside Bayview, the Supreme Court considered the ``language,
policies, and history'' of the Clean Water Act, including the
amendments in the 1977 Act, and unanimously upheld the Corps' exercise
of Clean Water Act jurisdiction over such adjacent wetlands. 474 U.S.
at 139. The Court held that the Corps' regulation defining ``the waters
of the United States'' to include wetlands adjacent to navigable waters
``is valid as a construction'' of the Clean Water Act. Id. at 131. The
Court first observed that ``between open waters and dry land may lie
shallows, marshes, mudflats, swamps, bogs--in short, a huge array of
areas that are not wholly aquatic but nevertheless fall far short of
being dry land.'' Id. at 132. To administer the statute, the Corps
therefore ``must necessarily choose some point at which water ends and
land begins.'' Id. The Court further explained that, in drawing that
jurisdictional line, the Corps may take into account ``the evident
breadth of congressional concern for protection of water quality and
aquatic ecosystems.'' Id. at 133. It quoted with apparent approval the
Corps' statement that ``Federal jurisdiction under Section 404 must
include any adjacent wetlands that form the border of or are in
reasonable proximity to other waters of the United States, as these
wetlands are part of this aquatic system.'' Id. at 134 (quoting 42 FR
37128, July 19, 1977). The Court concluded that ``the 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.'' Id.
    The Court also viewed the 1977 Act as specifically approving the
Corps' assertion of jurisdiction over adjacent wetlands--as considering
those wetlands to be ``waters'' themselves. Id. at 137-139. The Court
observed that ``the scope of the Corps' asserted jurisdiction over
wetlands was specifically brought to Congress' attention, and Congress
rejected measures designed to curb the Corps' jurisdiction in large
part because of its concern that protection of wetlands would be unduly
hampered by a narrowed definition of `navigable waters.''' Id. at 137.
The Court also cited section 404(g)(1) as express textual evidence
``that the term `waters' included adjacent wetlands.'' Id. at 138.
    Congress had good reason to approve the inclusion of adjacent
wetlands within the ``waters of the United States.'' In the 1986
regulations, the agencies determined that wetlands adjacent to
navigable waters generally play a key role in protecting and enhancing
water quality, explaining: ``Water moves in hydrologic cycles, and the
pollution of this part of the aquatic system, regardless of whether it
is above or below an ordinary high water mark, or mean high tide line,
will affect the water quality of the other waters within that aquatic
system. For this reason, the landward limit of Federal jurisdiction
under Section 404 must include any adjacent wetlands that form the
border of or are in reasonable proximity to other waters of the United
States, as these wetlands are part of this aquatic system.'' 42 FR
37128 (July 19, 1977); see also 38 FR 10834. See section IV.C.8.b of
this preamble for further discussion of the definition of ``adjacent.''
    As discussed below and further in section III.B of the Technical
Support Document, the best available science supports the 1986
regulations' conclusion that adjacent wetlands are part of the aquatic
ecosystem, and the agencies' construction of the Clean Water Act in
this rule, that adjacent wetlands that meet the relatively permanent
standard or the significant nexus standard affect the chemical,
physical, and biological integrity of paragraph (a)(1) waters by
performing essential functions, including providing valuable flood
control and water quality functions such as interruption and delay of
the transport of water-borne contaminants over long distances,
retention of sediment, prevention and mitigation of drinking water
contamination, and assurance of drinking water supply. As Congress
understood when it rejected efforts to narrow jurisdiction over
wetlands in

1977 and the Supreme Court recognized in Riverside Bayview, allowing
all adjacent wetlands to be filled without any permitting requirements
would deprive interconnected aquatic systems of those benefits and
thereby threaten the integrity of traditional navigable waters, the
territorial seas, and interstate waters. Wetlands are recognized as
``among the most important ecosystems on Earth.'' \48\ Among many other
public benefits, wetlands play an ``integral role'' in maintaining the
nation's ``water supply and quality.'' 16 U.S.C. 3901(a)(1). ``Research
has demonstrated repeatedly that natural wetlands enhance water
quality.'' \49\ Through chemical and biological processes, wetlands
trap and filter sediment, nutrients, and other pollutants that would
otherwise be carried into downstream waters.\50\ For example, wetlands
conservation is a crucial feature of the New York City municipal water
system, which provides high quality drinking water to millions of
people through watershed protection. New York protects adjacent
wetlands of its source waters rather than investing in extensive and
costly treatment. Wetlands also provide ``cost-effective flood
control,'' \51\ capturing overflow from rivers and streams during times
of high precipitation or snowmelt.\52\ For example, during Hurricane
Sandy in 2012, wetlands are estimated to have helped prevent $625
million in damage by protecting properties from flooding.\53\
---------------------------------------------------------------------------

    \48\ William J. Mitsch & James G. Gosselink, Wetlands (5th ed.)
at 3 (2015).
    \49\ National Research Council, Wetlands: Characteristics and
Boundaries (``NRC Report'') at 38 (1995).
    \50\ Virginia Carter, ``Wetlands Hydrology, Water Quality, and
Associated Functions,'' in National Water Summary, supra, at 44-45;
Science Report at ES-2 to ES-4.
    \51\ Carter, supra note 5050, at 44.
    \52\ See, e.g., NRC Report at 35; Mitsch & Gosselink, supra, at
539-541; Science Report at ES-2 to ES-4.
    \53\ Narayan, Siddharth, et al. 2017. The Value of Coastal
Wetlands for Flood Damage Reduction in the Northeastern USA.
Scientific Reports 7: 9463; Technical Support Document section II.C.
---------------------------------------------------------------------------

iii. It Is Reasonable for the Agencies To Continue To Include a
Provision To Cover Certain Waters That Do Not Fall Within Other
Jurisdictional Provisions
    For more than 45 years the agencies' regulations have included a
provision to address waters that did not fall within the categories it
established, such as tributaries and adjacent wetlands, because such
waters could have effects on water quality and on interstate commerce.
42 FR 37128 (July 19, 1977). This rule substantially revises this
provision by establishing that intrastate lakes and ponds, streams, or
wetlands not identified elsewhere in the rule may be determined to be
``waters of the United States'' if they meet either the relatively
permanent standard or the significant nexus standard. Therefore, under
this rule the agencies conclude that it is not appropriate to assert
jurisdiction over non-navigable, intrastate waters based solely on
whether the use, degradation, or destruction of the water could affect
interstate or foreign commerce. See section IV.C.6 of this preamble for
further discussion of the changes related to this provision. This rule
replaces the interstate commerce test with the relatively permanent
standard and the significant nexus standard.
    For more than four decades, the agencies' regulations defining
``waters of the United States'' have included provisions authorizing
case-specific determinations of jurisdiction over waters that did not
fall within the other jurisdictional provisions of the definition. The
Corps' 1975 interim final regulations addressed both ``intrastate
lakes, rivers, and streams that are used by interstate recreational
travelers, for the removal of fish sold in commerce, for interstate
industrial commercial purposes, or for the production of agricultural
commodities sold in commerce,'' and ``other waters that the District
Engineer determines necessitate regulation for protection of water
quality.'' 40 FR 31320, 31324 (July 25, 1975). As discussed above,
Congress was well-aware of the scope of the Corps' regulations when
adopting the 1977 Act.
    The rule properly authorizes case-specific consideration of certain
waters not covered by the categories established in the rule. As
discussed below and further in section IV.D of the Technical Support
Document, the best available science shows that some of these waters--
such as depressional wetlands, open waters, and peatlands--can provide
important hydrologic (e.g., flood control), water quality, and habitat
functions which can have effects on larger rivers, lakes, and
estuaries, including paragraph (a)(1) waters. The functions that
intrastate lakes and ponds, streams, and wetlands not identified in
paragraphs (a)(1) through (4) of this rule (i.e., paragraph (a)(5)
waters) can provide to paragraph (a)(1) waters include storage of
floodwater, recharge of ground water that sustains river baseflow,
retention and transformation of nutrients, metals, and pesticides,
export of organisms to paragraph (a)(1) waters, and habitats needed for
aquatic and semi-aquatic species that also utilize paragraph (a)(1)
waters. In addition, the agencies have never stated that the waterbody-
specific categories alone identify every jurisdictional water under the
Clean Water Act because in an area as vast and varied as the United
States, it is not possible to create an exhaustive list of waters that
provide these critical functions to paragraph (a)(1) waters. Indeed, a
clear example of waters that do not fall within any of the categories
are some lakes and ponds near jurisdictional tributaries or paragraph
(a)(1) waters. They are not wetlands (so do not fall within the
adjacent wetlands category), and many are not tributaries, but they are
very likely to meet either the relatively permanent standard or the
significant nexus standard. A lake that is not a tributary and is not a
wetland may have a continuous surface connection to a traditional
navigable water. It would not make sense to exclude such a lake from
jurisdiction as it would have many of the same effects on the
traditional navigable water as an adjacent wetland with the same
continuous surface connection. Likewise, a lake that is not a tributary
and is not a wetland may be near a jurisdictional tributary and
significantly affect a paragraph (a)(1) water by providing similar
functions as an adjacent wetland. Absent paragraph (a)(5) of this rule,
these lakes would meet either the relatively permanent standard or the
significant nexus standard, but would not fall within any of the
categories of waters established by the definition. Thus, where waters
do not fall within one of the more specific categories identified in
paragraph (a)(1) through (4) of this rule, the rule provides for such
waters to be evaluated for jurisdiction under paragraph (a)(5) and to
be jurisdictional if they meet either standard.
c. The Best Available Science Demonstrates That This Rule Properly
Advances the Objective of the Clean Water Act
    This rule is informed by the best available science on the
functions provided by waters, including wetlands, that are important
for the chemical, physical, or biological integrity of traditional
navigable waters, the territorial seas, and interstate waters. The
scientific literature extensively illustrates the effects tributaries,
adjacent wetlands, as well as intrastate lakes and ponds, streams, and
wetlands can and do have on the integrity of traditional navigable
waters, the territorial seas, and interstate waters. The relevant
science on the relationship and effects of streams, wetlands, and open
waters (such as lakes and ponds)

on larger downstream waters has continued to advance in recent years
and confirms the agencies' longstanding view that these waters should
be assessed for jurisdiction under the Clean Water Act. The Science
Report synthesized the peer-reviewed science regarding connectivity and
effects of streams, wetlands, and open waters to larger downstream
waters. Since the release of the Science Report, additional published
peer-reviewed scientific literature has strengthened and supplemented
the report's conclusions. The agencies have summarized and provided an
update on more recent literature and scientific support for this
section in the Technical Support Document section I.C. See also
Technical Support Document section III. This section summarizes the
best available science in support of the longstanding categories of the
1986 regulation, and in support of this rule and the agencies'
conclusion that this rule advances the objective of the Clean Water
Act. This section reflects the scientific consensus on the strength of
the effects that tributaries, adjacent wetlands, and paragraph (a)(5)
waters can and do have on traditional navigable waters, the territorial
seas, and interstate waters. Note that for purposes of this final rule,
the agencies have not made a categorical determination that all
tributaries, adjacent wetlands, and paragraph (a)(5) waters
significantly affect paragraph (a)(1) waters. See section IV.A.3.a.iii
(discussing the final rule's reliance on a case-specific approach to
assessing jurisdiction for certain types of waters) of this preamble.
    As the agencies charged with construing the statute, EPA and the
Corps must develop the outer bounds of the scope of the Clean Water
Act. Congress chose to delegate this authority to the expert agency
focused on environmental protection and, for the section 404 program,
to the agency with extensive permitting experience for discharges to
water. In section 501(a) of the Clean Water Act, Congress explicitly
delegated regulatory authority to EPA: ``The Administrator is
authorized to prescribe such regulations as are necessary to carry out
his functions under this Act.'' The Supreme Court in Riverside Bayview
recognized this decision by Congress and deferred to the agencies'
scientific expertise and judgement, finding that ``[i]n view of the
breadth of federal regulatory authority contemplated by the Act itself
and the inherent difficulties of defining precise bounds to regulable
waters, the 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.'' 474 U.S. at 134. Science alone cannot dictate where to draw
the line defining ``waters of the United States,'' but science is
critical to understanding what scope of jurisdiction furthers
Congress's objective to restore and maintain the chemical, physical,
and biological integrity of the nation's waters: only by relying upon
scientific principles to understand the way waters affect one another
can the agencies know whether they are achieving that objective.
Because the definition of ``waters of the United States'' should
advance the objective of the Clean Water Act and that objective is
focused on restoring and maintaining water quality, the best available
science informs this rule. See section IV.A.2 of this preamble; see
also section IV.B.3 of this preamble for the agencies' conclusion that
the 2020 NWPR was inconsistent with the best available science in
important ways.
i. Tributaries Can Provide Functions That Restore and Maintain the
Chemical, Physical, and Biological Integrity of Downstream Traditional
Navigable Waters, the Territorial Seas, and Interstate Waters
    Tributaries play an important role in the transport of water,
sediments, organic matter, nutrients, and organisms to downstream
paragraph (a)(1) waters. See Technical Support Document section III.A.
Tributaries slow and attenuate floodwaters; provide functions that help
maintain water quality; trap and transport sediments; transport, store,
and modify pollutants; and sustain the biological productivity of
downstream paragraph (a)(1) waters. Indeed, the Supreme Court has
recognized the importance of the physical integrity of upstream
tributaries in overcoming sedimentation hazards to navigation. United
States v. Rio Grande Dam & Irrigation Co., 174 U.S. 690 (1899).
Tributaries can provide these functions whether they are natural,
modified, or constructed and regardless of their flow regime.
    All tributary streams, including perennial, intermittent, and
ephemeral streams, are chemically, physically, and biologically
connected to larger downstream waters via channels and associated
alluvial deposits where water and other materials are concentrated,
mixed, transformed, and transported. The agencies note that while the
Science Report concluded such tributary streams were so connected, the
significant nexus standard is distinct from this scientific conclusion,
and the agencies are not in this rule concluding that all tributary
streams categorically meet the significant nexus standard. Streams,
even where seasonally dry, are the dominant source of water in most
rivers, rather than direct precipitation or groundwater input to
mainstem river segments. Within stream and river networks, headwater
streams make up most of the total channel length. The smallest streams
represent an estimated three-quarters of the total length of stream and
river channels in the United States.\54\ Because of their abundance and
location in the watershed, small streams offer the greatest opportunity
for exchange between the water and the terrestrial environment.
---------------------------------------------------------------------------

    \54\ The actual proportion may be much higher because this
estimate is based on the stream networks shown on the U.S.
Geological Survey (USGS) National Hydrography Dataset, which does
not show all headwater streams.
---------------------------------------------------------------------------

    In addition, compared with the humid regions of the country, stream
and river networks in arid regions have a higher proportion of channels
that do not flow perennially. For example, in Arizona, most of the
stream channels--96% by length--are classified as ephemeral or
intermittent. The functions that streams provide to benefit downstream
waters occur even when streams do not flow constantly. For example,
ephemeral headwater streams shape larger downstream river channels by
accumulating and gradually or episodically releasing stored materials
such as sediment and large woody debris.\55\ Due to the episodic nature
of flow in ephemeral and intermittent channels, sediment and organic
matter can be deposited some distance downstream in the arid Southwest
in particular, and then moved farther downstream by subsequent
precipitation events. Over time, sediment and organic matter continue
to move downstream and influence larger downstream waters. These
materials help structure downstream river channels by slowing the flow
of water

through channels and providing substrate and habitat for aquatic
organisms.
---------------------------------------------------------------------------

    \55\ Videos of ephemeral streams flowing after rain events in
the Southwest highlight how effective ephemeral streams can be in
transporting woody debris (e.g., tree branches) and sediment
downstream during the rainy season. See, e.g., U.S. Department of
Agriculture, Agricultural Research Service, Multiflume Runoff Event
August 1, 1990, https://www.tucson.ars.ag.gov/unit/WGWebcam/WalnutGulchWebcam.htm; U.S. Geological Survey, Post-fire Flash Flood
in Coronado National Memorial, Arizona (August 25, 2011), https://www.youtube.com/watch?v=qJ8JxBZt6Ws; Santa Clara Pueblo Fire/Rescue/
EMS Volunteer Department, Greg Lonewolf, #4 Santa Clara Pueblo Flash
Flood Event 01 Sept 2013 (April 14, 2017), https://www.youtube.com/watch?v=nKOQzkRi4BQ; Rankin Studio, Amazing Flash Flood/Debris Flow
Southern Utah HD (July 19, 2019), https://www.youtube.com/watch?v=_yCnQuILmsM.
---------------------------------------------------------------------------

    Stream and wetland ecosystems also process natural and human
sources of nutrients, such as those found in leaves that fall into
streams and those that may flow into creeks from agricultural fields.
Some of this processing converts the nutrients into more biologically
useful forms. Other aspects of the processing store nutrients, thereby
allowing their slow and steady release and preventing the kind of
short-term glut of nutrients that can cause algal blooms in downstream
rivers or lakes. Small streams and their associated wetlands play a key
role in both storing and modifying potential pollutants, ranging from
chemical fertilizers to rotting salmon carcasses, in ways that maintain
downstream water quality. Inorganic nitrogen and phosphorus, the main
chemicals in agricultural fertilizers, are essential nutrients not just
for plants, but for all living organisms. However, in excess or in the
wrong proportions, these chemicals can harm natural systems and humans.
Larger rivers process excess nutrients much more slowly than smaller
streams. Loss of nutrient retention capacity in headwater streams is
known to cause higher concentrations and loads of nitrogen and
phosphorus in downstream waterbodies. In freshwater ecosystems,
eutrophication, the enriching of waters by excess nitrogen and
phosphorus, sets off a chain reaction of events that reduces water
quality in streams, lakes, estuaries, and other downstream waterbodies.
The excess nutrients lead to the overabundance of algae and aquatic
plants. Too much algae clouds previously clear streams, such as those
favored by trout. Algal blooms not only reduce water column visibility,
but the microbial decay of algal blooms reduces the amount of oxygen
dissolved in the water, and therefore the amount available to aquatic
life, sometimes to a degree that causes fish kills. Fish are not the
only organisms harmed by eutrophication: some of the algae species that
grow in eutrophic waters generate tastes and odors or are toxic--a
clear problem for stream systems, reservoirs, and lakes that supply
drinking water for municipalities or that are used for swimming and
other contact-recreational purposes. Algal blooms driven by excess
nutrients also can injure people and animals, as toxins can kill native
fish and other wildlife, and endanger human health. Algal blooms can
also lead to beach closures. The overabundance of plant growth and
alterations in water chemistry that occur in eutrophic waters also
changes the composition of natural communities of aquatic ecosystems.
    Recycling organic carbon contained in dead plants and animals is
another crucial function provided by headwater streams and wetlands.
Ecological processes that transform inorganic carbon into organic
carbon and recycle organic carbon are the basis for every food web on
the planet. In freshwater ecosystems, much of the recycling happens in
small streams and wetlands, where microorganisms transform everything
from leaf litter and downed logs to dead salamanders into food for
other organisms in the aquatic food web. Like nitrogen and phosphorus,
carbon is essential to life but can be harmful to freshwater ecosystems
if it is present in excess or in the wrong chemical form. If all
organic material received by headwater streams and wetlands went
directly downstream, the glut of decomposing material could deplete
oxygen in downstream rivers, thereby damaging and even killing fish and
other aquatic life. The ability of headwater stream ecosystems to
transform organic matter into more usable forms helps maintain healthy
downstream ecosystems.
    Microorganisms in headwater stream systems use leaf litter and
other decomposing matter for food and, in turn, become food for other
organisms. For example, fungi that grow on leaf litter become
nutritious food for aquatic insects that make their homes on the bottom
of streams, including mayflies, stoneflies, and caddisflies. These
animals provide food for larger animals, including birds such as
flycatchers and fish such as trout. The health and productivity of
downstream traditional navigable waters, the territorial seas, and
interstate waters depend in part on processed organic carbon delivered
by upstream headwater systems.
    To be clear, the agencies recognize that SWANCC held that the use
of an abandoned sand and gravel pit by migratory birds was not by
itself a sufficient basis for the exercise of Federal regulatory
authority under the Clean Water Act. Consideration of biological
functions does not constitute an assertion of jurisdiction over a water
based solely on its use by migratory birds. Rather, the agencies
consider biological functions for purposes of significant nexus
determinations under this rule only to the extent that the functions
provided by tributaries, adjacent wetlands, and paragraph (a)(5) waters
significantly affect the biological integrity of the traditional
navigable waters, the territorial seas, or interstate waters. For
example, salmon are a critical component of the biological integrity in
certain paragraph (a)(1) waters, and they provide one of the clearest
illustrations of biological connectivity. To protect Pacific and
Atlantic salmon in traditional navigable waters (and their associated
commercial and recreational fishing industries), headwater streams must
be protected because Pacific and Atlantic salmon require both
freshwater and marine habitats over their life cycles and therefore
migrate along river networks. Many Pacific salmon species spawn in
headwater streams, where their young grow for a year or more before
migrating downstream, live their adult life stages in the ocean, and
then migrate back upstream to spawn. Even where they do not provide
direct habitat for salmon themselves, ephemeral streams may contribute
to the habitat needs of salmon by supplying sources of cold water that
these species need to survive (i.e., by providing appropriate physical
conditions for cold water upwelling to occur at downstream
confluences), transporting sediment that supports fish habitat
downstream, and providing and transporting food for juveniles and
adults downstream. These species thereby create a biological connection
along the entire length of the river network, demonstrating how the
upstream ephemeral waters can help to maintain the biological integrity
of the downstream traditional navigable water. Many other species of
anadromous fish (fish that are born in freshwater, spend most of their
lives in saltwater, and return to freshwater to spawn) like certain
lamprey, species of catadromous fish (fish that breed in the ocean but
that spend most of their lives in freshwater) like American eels, and
freshwater fish like rainbow trout and brook trout also require small
headwater streams to carry out life cycle functions. See Technical
Support Document sections III.A.iii and III.E.iv.
ii. Adjacent Wetlands Can Provide Functions That Restore and Maintain
the Chemical, Physical, and Biological Integrity of Traditional
Navigable Waters, the Territorial Seas, and Interstate Waters
    Adjacent wetlands provide valuable flood control and water quality
functions that affect the chemical, physical, and biological integrity
of paragraph (a)(1) waters including interruption and delay of the
transport of water-borne contaminants over long distances; retention of
sediment; retention and slow release of flood waters; and prevention
and mitigation of drinking water contamination and assurance of
drinking water supply. See

Technical Support Document section III.B. The agencies note that, while
the Science Report concluded such adjacent wetlands were so connected,
the significant nexus standard is distinct from this scientific
conclusion, and the agencies are not concluding in this rule that all
adjacent wetlands categorically meet the significant nexus standard.
    Because adjacent wetlands retain sediment and augment streamflow
via the gradual release of groundwater, stormwater, or water flowing
just beneath the soil surface, wetland loss correlates with increased
need for dredging and unpredictability of adequate streamflow for
navigation. Headwater wetlands are located where erosion risk is
highest and are therefore best suited to recapture and stabilize
manageable amounts of sediment that might enter traditional navigable
waters, the territorial seas, or interstate waters. Adjacent wetlands
naturally serve to recapture and stabilize sediment carried by streams
and rivers in times when flood flow distributes water across a
floodplain.
    Adjacent wetlands affect the integrity of paragraph (a)(1) waters
by retaining stormwater and slowly releasing floodwaters that could
otherwise negatively affect the condition or function of those
paragraph (a)(1) waters. The filling or draining of wetlands, including
those that are close to the stream network, reduces water storage
capacity in a watershed and causes runoff from rainstorms to overwhelm
the remaining available water conveyance system. The resulting stream
erosion and channel downcutting impair water quality and quickly drain
the watershed as surface water leaves via incised (deeper) channels.
Disconnecting the incised channel from the wetlands leads to more
downstream flooding. As the adjacent wetlands remain disconnected,
riparian vegetation and wetland functions are reduced. Moreover,
because less water is available in groundwater and wetlands for slow
release to augment streamflow during dry periods, the filling or
draining of wetlands can make the timing and extent of navigability on
some waterways less predictable during dry periods. Therefore, intact
adjacent wetlands, including headwater wetlands, can contribute to
maintaining navigability on the nation's rivers and harbors and can
reduce flooding in paragraph (a)(1) waters.
    Wetlands adjacent to tributaries of navigable waters, the
territorial seas, and interstate waters can also help promote
improvements in drinking water supply and quality. Over 228 million
people are served by nearly 15,000 public water systems using surface
water such as streams, rivers, lakes, tributaries, and surface-water
storage impoundments as a primary source of water.\56\ An estimated 61%
of water withdrawn for public water supply came from surface water
sources in 2015.\57\ Adjacent wetlands have an important role in
mitigating the risk of contamination to sources of drinking water, and
in water quality generally, due to their strategic location as buffers
for other waterbodies and their filtration of surface water. Retention
of water and its associated constituents by wetlands allows the
biochemical uptake and/or breakdown of contaminants and the destruction
of pathogens. The water retention capacity of adjacent wetlands also
allows for the storage and gradual release of surface waters that may
supply public water system intakes during times of drought. In either
case, this retention substantially improves both the supply and quality
of drinking water.
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    \56\ EPA data from 2022 Third Quarter Safe Drinking Water
Information System/Federal Version.
    \57\ Comments submitted by Association of Metropolitan Water
Agencies at 2 (February 4, 2022) (Docket ID No. EPA-HQ-OW-2021-0602-
0252), https://www.regulations.gov/comment/EPA-HQ-OW-2021-0602-0252
(citing Dieter, C.A., Maupin, M.A., Caldwell, R.R., Harris, M.A.,
Ivahnenko, T.I., Lovelace, J.K., Barber, N.L., and Linsey, K.S.,
2018, Estimated use of water in the United States in 2015: U.S.
Geological Survey Circular 1441. Retrieved from https://pubs.usgs.gov/circ/1441/circ1441.pdf).
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    Though drinking water supplied through public water supplies is
regulated by the Safe Drinking Water Act, many water suppliers also
rely on source water protection efforts under the Clean Water Act, as
the quality of the drinking water source is dependent on the protection
of its upstream waters. Conserving wetlands in source water protection
areas can help protect water quality, recharge aquifers, and maintain
surface water flow during dry periods. For example, wetlands
conservation is a crucial feature of the low-cost New York City
municipal water system, which provides high-quality drinking water to
millions of people through watershed protection, including of adjacent
wetlands, of its source waters rather than extensive treatment.
    Discharge of agricultural, industrial, sanitary, or other waste
into any surface water may pose a public health risk downstream. For
example, excessive upstream discharge may overwhelm a public water
system filtration unit, allowing microbial pathogens into the drinking
water system. EPA's Science Advisory Board cited drinking water
contamination by pathogens as one of the most important environmental
risks.\58\ Moreover, drinking water treatment to address microbial
pathogens has little effect on many toxic chemicals, metals, and
pesticides discharged into streams, drainage ditches, canals, or other
surface waters.
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    \58\ U.S. Environmental Protection Agency/Science Advisory
Board. 1990. Reducing Risk: Setting Priorities and Strategies for
Environmental Protection. SAB-EC-90-021. https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=2000PNG1.TXT.
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    In sum, adjacent wetlands can provide a variety of functions to
paragraph (a)(1) waters. Based on the importance of these functions to
paragraph (a)(1) waters, the agencies' interpretation of the Clean
Water Act to protect adjacent wetlands where those adjacent wetlands
meet either the relatively permanent standard or the significant nexus
standard reflects proper consideration of the objective of the Act and
the best available science.
iii. Intrastate Lakes and Ponds, Streams, or Wetlands Not Identified in
Paragraphs (a)(1) Through (4) of This Rule Can Provide Functions That
Restore and Maintain the Chemical, Physical, and Biological Integrity
of Traditional Navigable Waters, the Territorial Seas, and Interstate
Waters
    Intrastate lakes and ponds, streams, or wetlands not identified in
paragraphs (a)(1) through (4) of the rule--examples of which could
include, but are not limited to, prairie potholes, playa lakes, and
vernal pools--can provide important functions that affect the chemical,
physical, and biological integrity of paragraph (a)(1) waters. See
Technical Support Document section III.D. The agencies note that while
the Science Report concluded such intrastate lakes and ponds, streams,
and wetlands can provide these functions, the significant nexus
standard is distinct from this scientific conclusion, and the agencies
are not concluding in this rule that all intrastate lakes and ponds,
streams, and wetlands categorically meet the significant nexus
standard. These functions are particularly valuable when considered
cumulatively across the landscape or across different watershed or sub-
watershed scales. They are similar to the functions that adjacent
wetlands provide, including water storage to control streamflow and
mitigate downstream flooding; interruption and delay of the transport
of water-borne pollutants (such as excess nutrients and contaminants)
over long distances; and retention of sediment. These functions can be
important to the physical integrity of paragraph (a)(1) waters. For
non-

floodplain wetlands and open waters lacking a channelized surface or
regular shallow subsurface connection, generalizations from the
available literature about their specific effects on downstream waters
are difficult because information on both function and connectivity is
needed. Accordingly, a case-specific analysis of their effects on
paragraph (a)(1) waters is appropriate from both a scientific and
policy perspective.
    For example, oxbow lakes and other lakes and ponds that are in
close proximity to the stream network, that are located within
floodplain or riparian areas, or that are connected via surface and
shallow subsurface hydrology to the stream network or to other ``waters
of the United States'' perform critical chemical, physical, and
biological functions that affect paragraph (a)(1) waters. Like adjacent
wetlands, these waters individually and collectively affect the
integrity of paragraph (a)(1) waters by acting as sinks that retain
floodwaters, sediments, nutrients, and contaminants that could
otherwise negatively impact the condition or function of those
paragraph (a)(1) waters. They also provide important habitat for
aquatic species that utilize both the lake and pond and the nearby
paragraph (a)(1) water to forage, breed, and rest.
    Intrastate lakes and ponds, streams, and wetlands not identified in
paragraphs (a)(1) through (4) of the rule span the gradient of
connectivity identified in the Science Report. They can be open waters
located in the riparian area or floodplain of traditional navigable
waters, the territorial seas, and interstate waters (e.g., oxbow lakes)
and otherwise be physically proximate to the stream network (similar to
adjacent wetlands) or they can be open waters or wetlands that are
fairly distant from the network. They can also be connected to
paragraph (a)(1) waters through biological connections, such as through
the movement of aquatic and semi-aquatic species for habitat or other
lifecycle needs and can serve as sources of food for larger aquatic and
semi-aquatic animals that live in paragraph (a)(1) waters. See section
III.D of the Technical Support Document. These waters can also provide
additional functions such as storage and mitigation of peak flows,
natural filtration by biochemical uptake and/or breakdown of
contaminants, and, in some locations, high volume aquifer recharge that
contributes to the baseflow in paragraph (a)(1) waters. The strength of
functions provided by intrastate lakes and ponds, streams, and wetlands
that are evaluated under paragraph (a)(5) on paragraph (a)(1) waters
will vary depending on the type and degree of connection (i.e., from
highly connected to highly isolated) to paragraph (a)(1) waters and
landscape features such as proximity to stream networks and to such
waters with similar characteristics that function together to influence
paragraph (a)(1) waters.
    Since the publication of the Science Report in 2015, the published
literature has expanded scientific understanding and quantification of
the functions of these waters that affect the integrity of larger
waters, including traditional navigable waters, the territorial seas,
and interstate waters, particularly in the aggregate. More recent
literature (i.e., 2014-present, as some literature from 2014 and 2015
may not have been included in the Science Report) has determined that
non-floodplain wetlands can have demonstrable hydrologic and
biogeochemical downstream effects, such as decreasing peak flows,
maintaining baseflows, and performing nitrate removal, particularly
when considered cumulatively.
    Some intrastate lakes and ponds, streams, and wetlands not
identified in paragraphs (a)(1) through (4) can, in certain
circumstances, have strong chemical, physical, or biological
connections to and effects on paragraph (a)(1) waters. However, some
intrastate lakes and ponds, streams, and wetlands not identified in
paragraphs (a)(1) through (4) of this rule do not have significant
effects on paragraph (a)(1) waters because of their distance from
paragraph (a)(1) waters, their landscape position, climatological
variables, or other factors. The effect of distance on a significant
nexus analysis, for example, may vary based on the characteristics of
the aquatic resources being evaluated and other factors affecting the
strength of their connectivity to paragraph (a)(1) waters. Waters are
less likely to have a significant nexus if they are located outside of
the riparian area or floodplain, lack a confined surface or shallow
subsurface hydrologic connection to jurisdictional waters, or exceed
the minimum distances necessary for aquatic species that cannot
disperse overland to utilize both the subject waters \59\ and the
waters in the broader tributary network. However, sometimes it is their
lack of a hydrologic surface connection that contributes to the
important effect that they have on paragraph (a)(1) waters; for
example, depressional non-floodplain wetlands lacking surface outlets
can function individually and cumulatively to retain and transform
nutrients, retain sediment, provide habitat, and reduce or attenuate
downstream flooding, depending on site-specific conditions such as
landscape characteristics (e.g., slope of the terrain or permeability
of the soils). Justice Kennedy's insight that ``[g]iven the role
wetlands play in pollutant filtering, flood control, and runoff
storage, it may well be the absence of hydrologic connection (in the
sense of interchange of waters) that shows the wetlands' significance
for the aquatic system'' is consistent with the science. See Rapanos,
547 U.S. at 786 (Kennedy, J., concurring in the judgment).
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    \59\ In this preamble, the agencies use ``subject waters'' to
mean the water or waters being assessed for jurisdiction. ``Subject
waters evaluated pursuant to the significant nexus standard'' means
the water either alone or in combination with similarly situated
waters in the region.
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    Based on the functions that can be provided by intrastate lakes and
ponds, streams, and wetlands not identified in paragraphs (a)(1)
through (4) to traditional navigable waters, the territorial seas, and
interstate waters, assessing these waters to determine whether they
meet either the relatively permanent standard or the significant nexus
standard reflects proper consideration of the objective of the Clean
Water Act and the best available science.
3. The Scope of This Rule Is Limited Consistent With the Law, the
Science, and Agency Expertise
    In this rule, the agencies are exercising their authority to
construe ``waters of the United States'' to mean the waters defined by
the familiar 1986 regulations with amendments to reflect the agencies'
interpretation of the statutory limits on the scope of the ``waters of
the United States.'' This construction is supported by consideration of
the text of the relevant provisions of the Clean Water Act and the
statute as a whole, the scientific record, relevant Supreme Court
decisions, 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.'' This rule's
limitations are based on the agencies' conclusion 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 agencies have also determined
that the relatively permanent standard should be included in the rule
because, while it identifies only a subset of the ``waters of the

United States,'' it provides important efficiencies and additional
clarity for regulators and the public.
    This section of the preamble first explains the agencies'
conclusion that utilization of both the relatively permanent standard
and the significant nexus standard gives effect to the Clean Water
Act's text, including its objective as well as its limitations. The
significant nexus standard is consistent with the text, objective, and
legislative history of the Clean Water Act, as well as relevant Supreme
Court case law and the best available science. The relatively permanent
standard is administratively useful as it more readily identifies a
subset of waters that will virtually always significantly affect
paragraph (a)(1) waters, but standing alone the standard is
insufficient to meet the objective of the Clean Water Act. This section
also explains that fact-based standards for determining Clean Water Act
jurisdiction are appropriate and not unusual under the Act. The
agencies have the discretion to consider defining waters as
jurisdictional on a categorical basis where scientifically and legally
justified (for example in this rule, paragraph (a)(1) waters and their
adjacent wetlands) or on a case-specific, fact-based approach (for
example, in this rule, tributaries and their adjacent wetlands that
meet the relatively permanent standard or significant nexus standard).
Finally, this section explains how this rule reflects full and proper
consideration of the water quality objective in section 101(a) and the
policies relating to responsibilities and rights of Tribes and States
under section 101(b) of the Clean Water Act. Based on these
considerations, the agencies have concluded that the significant nexus
standard in this rule is the best interpretation of section 502(7) of
the Act.
a. The Limitations Established by This Rule Advance the Objective of
the Clean Water Act
    This rule's utilization of both the relatively permanent standard
and the significant nexus standard gives effect to the Clean Water
Act's text and environmentally protective objective as well as its
limitations. See Rapanos, 547 U.S. at 767-69 (Kennedy, J., concurring
in the judgment) (observing ``the evident breadth of congressional
concern for protection of water quality and aquatic ecosystems'' and
referring to the Clean Water Act as ``a statute concerned with
downstream water quality'' (citations omitted)); Riverside Bayview, 474
U.S. at 133 (``Congress chose to define the waters covered by the Act
broadly.''). The agencies, however, have concluded that it is the
significant nexus standard that advances the objective of the Clean
Water Act because it is linked to effects on the water quality of
paragraph (a)(1) waters while also establishing an appropriate
limitation on the scope of jurisdiction by requiring that those effects
be significant. The relatively permanent standard is administratively
useful as it more readily identifies a subset of waters that will
virtually always significantly affect paragraph (a)(1) waters, but,
exclusive reliance on the standard for all determinations is
inconsistent with the text of the statute and Supreme Court precedent
and is insufficient to advance the objective of the Clean Water Act.
    With this rule, the agencies conclude that if a water meets either
the relatively permanent standard or the significant nexus standard, it
falls within the protections established by the Clean Water Act. As
discussed earlier, this rule is not based on an application of the
Marks test for interpreting Supreme Court decisions; rather, with this
rule, the agencies are interpreting the scope of the definition of
``navigable waters,'' informed by relevant Supreme Court precedent, but
also based on the text of the relevant provisions of the Clean Water
Act and the statute as a whole, the scientific record, 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.''
    This section first discusses why the significant nexus standard is
consistent with the text, objective, and legislative history of the
Clean Water Act, as well as relevant Supreme Court case law and the
best available science; then explains why the relatively permanent
standard is administratively useful but on its own is insufficient;
and, finally, explains that fact-based standards for determining Clean
Water Act jurisdiction are appropriate and not unique to the definition
of ``waters of the United States.''
i. The Significant Nexus Standard Is Consistent With the Text and
Objective of the Clean Water Act, Legislative History, Case Law, and
the Best Available Science
    The significant nexus standard, as the agencies have established it
in this rule, is the best interpretation of the Clean Water Act because
it is consistent with the text, including the Act's statutory objective
and statutory structure, the legislative history and case law, and is
supported by the best available science. The standard is consistent
with the plain language of the Act's objective because it is based upon
effects on the water quality of paragraph (a)(1) waters and limits the
scope of jurisdiction based on the text of that objective. Moreover,
protection of waters that significantly affect the paragraph (a)(1)
waters--i.e., traditional navigable waters, the territorial seas, and
interstate waters--is consistent with the scope of Commerce Clause
authority that the Supreme Court in SWANCC concluded that Congress was
exercising, while also fulfilling Congress's intent in exercising that
authority in enacting the Clean Water Act.
    The significant nexus standard effectuates the text of Clean Water
Act section 502(7), which defines ``navigable waters'' as ``the waters
of the United States, including the territorial seas.'' The standard is
properly focused on protecting paragraph (a)(1) waters, which are the
foundation of the Clean Water Act: traditional navigable waters (which
``navigable waters'' clearly invokes but is not limited to); ``the
territorial seas'' (which are explicitly listed in section 502(7)); and
interstate waters (which are unambiguously waters ``of the United
States,'' as they are waters of the ``several States,'' U.S. Const.
section 8). Further, each of the rule's provisions identifies an
aquatic resource that meets the definition of ``water'' or ``waters''
in either the Rapanos plurality's preferred dictionary or the
dictionary most contemporaneous with the passage of the Clean Water
Act. See section IV.A.3.a.ii of this preamble for discussion of the
plurality's dictionary-based analysis. The first definition of
``water'' within Webster's Second (1.a. of the definition) is ``[t]he
liquid which descends from the clouds in rain and which forms rivers,
lakes, seas, etc.,'' Webster's New International Dictionary 2882 (2d
ed. 1954). The definition of ``waters,'' plural, in the most
contemporaneous Webster's, is: ``the water occupying or flowing in a
particular bed.'' Webster's Third New Intl. (1966). Even the Rapanos
plurality's preferred definition includes ``water as found in
`streams,' '' ``water `[a]s found in streams and bodies forming
geographical features such as oceans, rivers, [and] lakes,' or `the
flowing or moving masses, as of waves or floods, making up such streams
or bodies.' '' Rapanos, 547 U.S. at 732-33 (quoting Webster's New
International Dictionary 2882, definition 2.c). Traditional navigable
waters; interstate waters; the territorial seas; impoundments of
waters; tributaries; adjacent wetlands; and intrastate lakes and ponds,
streams, and wetlands are ``water'' or ``waters'' under these
definitions, as identified by hydrologists

and other scientists, and in practice. Moreover, with respect to
whether wetlands are waters, that question has already been resolved by
both science and a unanimous Supreme Court in Riverside Bayview. 474
U.S. at 137-39. The requirement that a significant nexus exist between
upstream waters, including wetlands, and ``navigable waters in the
traditional sense'' thus clearly advances Congress's stated objective
in the Act while fulfilling ``the need to give the term `navigable'
some meaning.'' Rapanos, 547 U.S. at 779 (Kennedy, J., concurring in
the judgment). See also section IV.C.2.b.iii of this preamble for