August 12, 2022


Let'S Talk Law

Will “Significant Nexus” Again Define Waters Of The United States? – Environment

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The U.S. Environmental Protection Agency and the U.S. Department
of the Army Corps of Engineers (the Agencies) recently announced
they will take another run at defining “waters of the United
States” (WOTUS). This is key to the scope of federal
permitting and enforcement jurisdiction under the Clean Water Act
(CWA). The Biden administration first seeks to reinstate the
“significant nexus” regime, then create an
“enduring” definition of WOTUS.1 All
indications are, however, that uncertainty and litigation will
continue for the foreseeable future. Even the first step will
be subject to legal challenge.


On July 30, 2021, the EPA and the Army Corps announced plans to
engage stakeholders in another process revising the definition of
“waters of the United States” under the
CWA.2The “WOTUS” term is not defined by the
statute. Instead, it has been defined by the Agencies through
regulations since the 1970s. Regulations promulgated in 1986 were
the foundation until a revision finalized by the Obama
administration in 2015. Since then, the “WOTUS”
definition has been altered several times, each resulting in legal

Certain states and other plaintiffs challenged the Agencies’
2015 WOTUS rule. This version of WOTUS aimed to implement Justice
Kennedy’s “significant nexus” test from his
concurrence in Rapanos v. United
.3 Several courts concluded that the
plaintiffs’ challenges were likely to succeed and blocked the
implementation of the 2015 rule in much of the country. In 2019,
two courts, and then the EPA, found that the Agencies’ 2015
WOTUS rule was procedurally or substantively unlawful. The Agencies
repealed it.4 The Agencies then promulgated a new
definition for “WOTUS” in 2020, known as the Navigable
Waters Protection Rule.

A number of plaintiff states and organizations challenged the
2020 rule in courts across the country. But efforts to enjoin
implementation of the 2020 rule nationwide were this time rejected
by federal courts. In March 2021, an injunction issued by a lone
district court in the state of Colorado was vacated in the Tenth
Circuit.5 Thus, no court currently holds that the
Agencies’ 2020 WOTUS rule is unlawful.  


The current definition of “WOTUS” was promulgated in
the Navigable Waters Protection Rule. There are now generally four
categories of waters that are federally regulated:

  • territorial seas and traditional navigable waters;

  • perennial and intermittent tributaries to those waters;

  • certain lakes, ponds, and impoundments; and

  • wetlands adjacent to jurisdictional waters6

A particular area of dispute with the 2020 Rule was the
Agencies’ categorical exclusion of ephemeral

The Biden administration plans to rescind the 2020 Navigable
Waters Protection Rule, stating that it is “leading to
significant environmental degradation.”8 This
is primarily based on the exclusion of ephemeral waters from
federal jurisdiction, leaving that regulation to states,
localities, and tribes. The Biden administration says it will issue
its own new definition. The new round of revisions to the
“WOTUS” definition will involve two proposed rulemakings.
First, the EPA and the Army Corps plan to issue a
“foundational rule” to restore the 1986 definition of
“WOTUS” that was in effect until 2015, when the Obama
administration redefined “WOTUS.” This would, in effect,
restore the “significant nexus” regime that existed after
the Supreme Court’s 2006 Rapanos  decision.
Then, the Agencies will issue a second, separate rulemaking again
redefining “WOTUS.”9


The Agencies have given little indication about how they might
again redefine the definition of “waters of the United
States” to create a “durable” rule. It is certain,
however, that even the Agencies’ announced first step of
promulgating a “foundational rule” restoring the 1986
definition will be met with legal challenges.

The 1986 regime was criticized—then judicially limited
through as-applied legal challenges—for being overbroad and
ambiguous. Supreme Court decisions found that those regulations
asserted jurisdiction over waters exceeding the scope of the CWA.
These include the SWANCC decision in 2001 and
the Rapanos  decision in 2006.
In SWANCC, the Supreme Court decided that isolated,
abandoned sand and gravel pits with seasonal ponds are not WOTUS.
The majority opinion, written by Chief Justice Rehnquist, relied on
the meaning of the term “navigable,” which the majority
found implied a connection to traditionally navigable
waters.10 In Rapanos, the Supreme
Court examined whether WOTUS includes a wetland that occasionally
empties into a tributary of a traditionally navigable
water.11 The Supreme Court did not produce a
majority decision. While five justices opined against the
Army’s interpretation, two different tests were put forth.
Justice Scalia’s plurality opinion held that a mere
“hydrological connection” is not enough to qualify a
wetland as a WOTUS; a continuous surface connection is needed.
Justice Kennedy, on the other hand, proposed a “significant
nexus” to a traditionally-navigable-waterway rule in his
concurring opinion until a more precise rule might be adopted.
Notably, the Rapanos  decision featured a
concurrence by Chief Justice Roberts. Roberts was critical of the
Agencies’ attempt to “adhere to [their] essentially
boundless view of the scope of [their] power” in the wake
of SWANCC and failure to timely amend the 1986
regulations and “develop[] some notion of an outer bound to
the reach of their authority.”12

the Chevron doctrine,13 judicial
deference is given to an agency’s interpretation of a statute
so long as (1) Congress has not unambiguously answered the question
in the statute after judicial application of the tools and canons
of statutory construction for first determining what Congress
itself intended (Chevron  Step One) and (2) the
agency’s interpretation of the statute is reasonable. Here,
when repealing the 2015 Obama-era rule, the Agencies asserted that
the 2015 WOTUS rule was prohibited by the statutory text of the
CWA, as reflected by the Supreme Court’s decisions
in SWANCC  and Rapanos. Yet the
Agencies’ recent announcement does not suggest that the text of
CWA unambiguously prohibits the current Navigable Waters Protection
Rule at Chevron Step One. 

In the absence of a claim that the CWA requires the Agencies to
repeal the Navigable Waters Protection Rule, certain states and
litigants are likely to challenge even a temporary return to the ad
hoc regulatory regime founded on the 1986-era regulations would be
arbitrary and capricious and without substantial justification. A
proposed “foundational rule” will likely be claimed to
“rest[] upon factual findings that contradict those which
underlay its prior policy.”14 The challengers
will likely note that in such a case, “or when [the
Agencies’] prior policy has engendered serious reliance
interests that must be taken into account,” the Supreme Court
holds that the Agencies must “provide a more detailed
justification than what would suffice for a new policy created on a
blank slate.”15

Moreover, the CWA features criminal penalties. Therefore, the
rule of lenity is likely to be asserted as another statutory,
interpretative bar to the Agencies’ first step. This rule of
statutory construction generally requires a court to resolve an
unclear or ambiguous statutory question in favor of a criminal
defendant. The “significant nexus” test that became the
keystone of the 1986-era regulations does not appear in
text of the CWA. There may also be constitutional challenges
under the “void-for-vagueness
doctrine.”16 This doctrine “guarantees
that ordinary people have ‘fair notice’ of the conduct a
[law] proscribes” and “guards against arbitrary or
discriminatory law enforcement by insisting that a [law] provide
standards to govern the actions of police officers, prosecutors,
juries, and judges.”17

The “significant nexus” regime originally came about
as judicial gloss on the 1986 regulations imposed by as-applied
legal challenges constraining the regulatory text. Those
regulations were not facially challenged or vacated in total
in SWANCC  or Rapanos 
because of the statute of limitations. A plan to repromulgate the
1986 regulations now will confront facial legal challenges.
Litigants are likely to challenge the Agencies’ attempts to
intentionally reimpose the regulatory regime that has not
successfully clarified the “notoriously unclear” reach of
the CWA as contrary to statutory text
at Chevron  Step One and
unconstitutional.18 Even Justice Kennedy later
expressed concern about how the CWA, as implemented by the Agencies
using the significant nexus test, “raise[d] troubling
questions regarding the Government’s power to cast doubt on the
full use and enjoyment of private property throughout the


  • The Biden administration announced a two-step rulemaking
    process to revise the “WOTUS” definition. It will include
    (1) repealing the Navigable Waters Protection Rule and returning to
    the 1986 “significant nexus” regime, followed by (2) a
    separate rulemaking revising the “WOTUS” definition.

  • Actions to revoke the current Navigable Waters Protection Rule
    and revise the “WOTUS” definition will continue to face
    legal challenges, as with the prior WOTUS rule rewrites.

  • Even the Agencies’ proposed first step of issuing a
    “foundational rule” to reinstate the 1986-era regulations
    is likely to face legal challenges.

* Jonathan D. Brightbill served at U.S. Department of
Justice from 2017 to 2021, including as Acting Assistant
Attorney General of the Environmental and Natural Resources
Division. Please note that government orders on the federal, state,
and local level are changing every day, and the information
contained herein is accurate only as of the date set forth


1 EPA and Army Announce Next Steps for Crafting
Enduring Definition of Waters of the United States
, EPA (July
30, 2021),

2 Id.

3 Rapanos v. U.S. s, 547 U.S. 715 (2006)
(Kennedy, J., concurring).

4 84 Fed. Reg. 56,626 (Oct. 22, 2019).

5 Colorado v. U.S. EPA, 989 F.3d
874 (10th Cir. 2021).

 CFR pt. 328.

7 Trump Water Rule Will Remain In Place During
, Law 360 (July 15, 2021, 3:34 PM EDT),

8 EPA, Army Announce Intent to Revise Definition of
, EPA (June 9, 2021),

9 Id.

10 Solid Waste Agency of N. Cook Cnty. v. U.S.
Army Corps of Eng’rs
, 531 U.S. 159 (2001).

11 Rapanos v. U.S., 547 U.S. 715

12 Id. at 757-58 (Roberts, C.J.,

13 Chevron U.S.A.
 v. Nat. Res. Def. Council,
 467 U.S. 837 (1984).

14 F.C.C. v. Fox, 556 U.S. 502, 515

15 Id.

16 Sessions v. Dimaya, 138 S. Ct. 1204,
1212 (2018).

17 Id.

18 Sackett v. EPA, 566 U.S. 120, 133 (2012)
(Alito, J., concurring).

19 U.S. Army Corps of Eng’rs v. Hawkes
., 136 S. Ct. 1807, 1816-17 (2016) (Kennedy, J.,

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