Clearer Water Ahead? EPA and Army Corps Seek Comment on Key WOTUS Terms

On September 9, 2026, the U.S. Environmental Protection Agency (“EPA”) and the U.S. Army Corps of Engineers (“Army Corps”) issued a Supplemental Notice of Proposed Rulemaking (the “Supplemental Proposal”) seeking public comment on additional regulatory alternatives to be considered as the agencies work to update the definition of waters of the United States (“WOTUS”). The Supplemental Proposal follows the Trump administration’s initial Proposed Rule, issued on November 20, 2025, to align the definition of WOTUS with the Supreme Court’s 2023 decision in Sackett v. EPA.¹ This development marks the sixth WOTUS rulemaking in the past decade and seeks public input on several key definitions set forth in the Proposed Rule. Following over 220,000 comments received over the past ten months, the Supplemental Proposal provides alternative definitions for “relatively permanent,” “perennial waters,” and “continuous surface connection”—terms that are key to marking the reach of federal jurisdiction over the nation’s waters. These definitions are intended to provide greater certainty to the regulated community by establishing bright-line tests and further the Trump administration’s goals of streamlining project development.

Key Takeaways

The alternative definitions proposed in the Supplemental Proposal would narrow the scope of federal jurisdiction over waters and wetlands, excluding most intermittent streams and seasonally inundated wetlands from federal regulation. The initial Proposed Rule would use the concept of a “wet season” as an element of determining what features had water for periods long enough to justify federal jurisdiction. Many commenters raised concerns with this approach. The proposal tries to fix this by replacing the “wet season” concept with bright-line limits. The ultimate goal is to make it easier for landowners and developers to determine when a permit may be required from the Army Corps for construction and development activities.

Why this Proposal is Important

The Clean Water Act (“CWA”) prohibits unpermitted discharges of pollutants from certain sources into “navigable waters,” defined in the statute as the “waters of the United States, including the territorial seas.” The CWA imposes significant potential civil and criminal penalties, even for unintentional violations, and many private landowners and developers struggle for clarity on whether activities or development on their land require that they go through the lengthy and expensive process of getting a permit from the Army Corps.

As a Supreme Court justice wrote a few years ago, the meaning of WOTUS is “notoriously unclear,” with “crushing” “consequences . . . even for inadvertent violations.”² Unsurprisingly, the issue has reached the Supreme Court numerous times since 1973. Most recently, in Sackett, the Court clarified that for wetlands, the CWA’s jurisdiction extends only to those that are adjacent to “relatively permanent bod[ies] of water connected to traditional interstate navigable waters” such that the wetland has a “continuous surface connection” with that water, making it “difficult to determine where the ‘water’ ends and the ‘wetland’ begins.”³ The Sackett decision came shortly after the Biden administration had proposed a more expansive rewrite of the WOTUS definition, and although the administration quickly issued a conforming rule to implement the Sackett decision, there remains ample confusion about the true extent of federal jurisdiction. For example, the conforming rule did not resolve ambiguities related to a number of key terms, such as “relatively permanent” and “continuous surface connection.”⁴ The Trump administration’s November 2025 Proposed Rule and the Supplemental Proposal aim to bring clarity to this vague language.

Key Developments in the Supplemental Proposal

The Trump administration’s initial rulemaking effort in November 2025 aimed to, among other changes, provide new definitions for key terms that had been left subject to varying interpretations.

Relatively Permanent. Whether a water is “relatively permanent” is a key threshold in determining whether it is covered by the CWA. The Proposed Rule defined “relatively permanent” as “standing or continuously flowing bodies of surface water that are standing or continuously flowing year-round or at least during the wet season.” The “wet season” concept may have been formulated in response to the plurality’s statement in Rapanos v. United States that “relatively permanent” waters did not “necessarily exclude seasonal rivers, which contain continuous flow during some months of the year but no flow during dry months.”⁵ The Proposed Rule’s introduction of the “wet season” concept without definition indicated that agencies (or the landowner) would be required to consider the climate hydrology and topography of the region to determine whether waters were jurisdictional. The Proposed Rule suggested a test assessing months in which precipitation exceeds evaporation and solicited comments on how to best identify the wet season for individual locations.

Commenters raised significant concerns with the “wet season” concept, noting that nothing in the CWA, Sackett, or prior Supreme Court precedent set forth a “wet season” standard, and they expressed concern that this concept would be difficult to implement given the lag time between precipitation and wetland inundation and other regional variations. Responding to these comments, the Supplemental Proposal puts forth an additional option that removes the “wet season” concept entirely. Under this option, “relatively permanent” waters would generally include only “perennial” waters—waters that flow year-round—with certain exceptions to account for brief interludes and anomalous events. Indeed, the Supplemental Proposal defines “perennial” as waters that have “standing or continuously flowing water every day of the year during ordinary conditions.” The agencies also seek comment on whether the term should instead be defined as “surface water flowing continuously year-round,” as was the case in the first Trump administration’s 2020 Navigable Waters Protection Rule. Applying the terms “relatively permanent” and “perennial” in this way would narrow the jurisdictional reach of the CWA by focusing on features that nearly always contain standing or flowing water, and not on intermittent, ephemeral, or dry features that only carry flows in response to precipitation.

The additional option seeks to provide greater certainty and ease of implementation for the regulated community. Unlike previous WOTUS rulemakings that did not define any minimum duration of flow needed to qualify as “relatively permanent,” the Supplemental Proposal would clarify that waters could experience an interruption of flow for no more than 30 consecutive days in any given year while retaining jurisdictional status. Anomalous events, like a drought or dry spell, would also not affect a waterbody’s status. The Army Corps and EPA are considering treating only extreme and exceptional droughts that extend for no more than a continuous, five-year period, as “anomalous.” The agencies describe the supplemental option as a “predictable, transparent, and easy to administer” approach that would “obviate the need for property owners ‘to retain an expensive expert consultant’” to determine jurisdiction.

Continuous Surface Connection. In Sackett, the court held that wetlands are jurisdictional when they are practically “indistinguishable” from WOTUS. However, the Proposed Rule did not clearly incorporate this concept, instead proposing to define “continuous surface connection” as “having surface water at least during the wet season and abutting . . . a jurisdictional water,” in a callback to guidance the agencies released in March 2025. The Supplemental Proposal would define this term to mean “perennial surface water in a wetland that is continuously connected with the surface water in the jurisdictional water such that it is difficult to determine where the jurisdictional water ends and the wetland begins” and would remove references to the “wet season” in an effort to avoid regulatory uncertainty and hew closer to the Supreme Court’s instruction in Sackett. The agencies clarified that only portions of a wetland that are “indistinguishably part of a jurisdictional water”—that is, wetlands with a continuous surface water connection to a WOTUS—would themselves be jurisdictional. This framework would narrow the jurisdictional reach over wetlands by excluding portions that meet the three technical criteria to be a wetland (i.e., hydrophytic vegetation, hydric soils, and wetland hydrology) but lack flowing or standing water. Wetlands would also be subject to the same anomalous and 30-day non-anomalous exceptions noted above. The agencies are also seeking comment on whether the terms “adjacent” and “abutting” are relevant to determining jurisdiction given Sackett’s indistinguishability concept.

Implications for Landowners and Developers

These proposals continue the Trump administration’s efforts to streamline permitting and promote development, including domestic energy development. With fewer water features subject to federal jurisdiction, projects that may have otherwise been subject to costly and burdensome permitting programs may be able to avoid these requirements altogether. The proposed rule, combined with the Army Corps’ recent reissuance of Nationwide Permits, the EPA’s pending proposal to clarify Section 401 water quality certifications, and expedited permitting options across numerous federal agencies sets the stage for continued infrastructure development. Property owners and project developers should keep an eye out for further developments.

Public Involvement

The EPA and the Army Corps will accept public comments on the Supplemental Proposal through October 9, 2026. Specifically, the agencies are requesting public input on the applicability and implementation of the definitions of “relatively permanent,” “perennial,” and “continuous surface connection.” Comments can be submitted to the agencies by mail, email, hand delivery, or online at regulations.gov on docket no. EPA-HQ-OW-2025-0322. Vinson & Elkins can assist interested parties in developing a comment strategy to ensure their viewpoints are part of the rulemaking process.

¹598 U.S. 651 (2023).

²U.S. Army Corps of Engineers v. Hawkes Co., Inc., 578 U.S. 590, 602 (2016) (Kennedy, J., concurring)

³598 U.S. at 678–79.

⁴With the Biden administration’s rules challenged in federal district courts in West Virginia, Kentucky, and Texas, the EPA is currently implementing a patchwork approach to WOTUS, with the September 2023 rule in force in 24 states and a pre-2015 regulatory regime used in the remaining states.

⁵547 U.S. 715, 732 n.5 (2006).

This information is provided by Vinson & Elkins LLP for educational and informational purposes only and is not intended, nor should it be construed, as legal advice.