Will "Significant Nexus" Again Define Waters Of The United States?

Published date12 August 2021
Subject MatterEnvironment, Energy and Natural Resources, Environmental Law, Water
Law FirmWinston & Strawn LLP
AuthorMr Jonathan D. Brightbill and Madalyn G. Brown

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 challenges.

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 States.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 The Agencies repealed it.4 The Agencies then promulgated a new definition for "WOTUS" in 2020, known as the Navigable Waters Protection Rule.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
  • ...

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