EPA and Army Corps Issue Supplemental WOTUS Proposal: How It Could Affect Your Projects

On September 9, 2026, the U.S. Environmental Protection Agency (EPA) and the U.S. Department of the Army, including the U.S. Army Corps of Engineers (the "Corps," collectively with EPA, the "Agencies") published a Supplemental Notice of Proposed Rulemaking (Supplemental Proposed Rule) addressing the definition of "waters of the United States" (WOTUS) as used under the Clean Water Act (CWA). The Supplemental Proposed Rule augments targeted portions of the Agencies' November 20, 2025 Notice of Proposed Rulemaking (NPRM), effectively and further narrowing jurisdictional WOTUS following the Supreme Court's decision in Sackett v. Environmental Protection Agency, 598 U.S. 651 (2023) (Sackett), after receiving and reviewing approximately 220,000 comments.

The most immediate practical takeaway is that the Supplemental Proposed Rule would not change current law or permitting obligations; rather, it seeks additional public comment before final action. Stakeholders should evaluate potential effects of the Supplemental Proposed Rule on Section 404 permitting and mitigation, Section 402 NPDES permitting, Section 401 certification, and potential downstream impacts on state and Tribal programs.

Any comments on the Supplemental Proposed Rule must be received by October 9, 2026. The deadline creates an urgent opportunity to address the proposed perennial-only standard, the 30-day interruption rule, the five-year drought concept, and potential effects on projects and state or Tribal programs.

Overview of the Supplemental Proposed Rule

The Agencies say the Supplemental Proposed Rule is intended to provide greater certainty in implementing the post-Sackett WOTUS framework.

What the Supplemental Proposed Rule Would Add

The Supplemental Proposed Rule would add several new definitions.

First, the Agencies propose defining "relatively permanent" as "perennial bodies of water," with standing or continuously flowing water every day of the year during ordinary conditions. Moreover, a perennial water body would retain that jurisdictional status under two scenarios. Under the first scenario, a perennial water would remain a jurisdictional WOTUS if flow is interrupted by an anomalous event, such as drought or an unusual dry spell (the Agencies are considering whether only extreme (D3) and exceptional (D4) droughts should qualify as anomalous events), so long as the interruption lasts no more than five years. After five years of a continuous anomalous event, a perennial water body would no longer be considered jurisdictional because the interruption will no longer be deemed anomalous. Under a second scenario, an otherwise perennial water body would retain its jurisdictional status where non-anomalous events occur, such as low tide or a regularly occurring dry spell, so long as the event only lasts for a single period of up to 30 consecutive days in any given year.

Second, the Agencies propose defining "continuous surface connection" to require perennial surface water in a wetland that is continuously connected to the surface water of a jurisdictional water, making it difficult to determine where the jurisdictional water ends and the wetland begins. The same anomalous and non-anomalous interruption concepts included in the "relatively permanent" definition would apply to "continuous surface connection." Only that portion of the wetland that is indistinguishably part of the jurisdictional water would be jurisdictional. The Agencies anticipate that the majority of wetlands currently treated as jurisdictional under the adjacent wetlands regimes would no longer satisfy this proposed supplemental definition.

Third, the Agencies propose defining "perennial" as "having standing or continuously flowing water every day of the year during ordinary conditions."

Departure from Sackett's Formulation

Although the Supplemental Proposed Rule invokes the Sackett majority's "relatively permanent" language, the proposed "perennial" standard arguably narrows that concept more than Sackett facially required. Sackett borrowed the phrase "relatively permanent" from Justice Scalia's plurality opinion in Rapanos v. United States, 547 U.S. 715 (2006) (Rapanos), which stated that WOTUS encompasses "only those relatively permanent, standing or continuously flowing bodies of water 'forming geographic[al] features' that are described in ordinary parlance as 'streams, oceans, rivers, and lakes.'" The qualifier "relatively" indicates something less than absolute permanence, and the Rapanos plurality expressly noted that its test did not "necessarily exclude streams, rivers, or lakes that might dry up in extraordinary circumstances, such as drought." Justice Scalia's Rapanos plurality also acknowledged that "seasonal rivers" could qualify as relatively permanent where they "chann[el] water in a permanent channel"—a concession that leaves room for waters flowing continuously for extended periods but not every day of the year, a key factor in many arid western jurisdictional waters.

The above statements leave room for argument that "relatively permanent" was intended only to exclude ephemeral or ordinarily dry channels, but not necessarily every waterbody lacking uninterrupted year-round flow. Sackett adopted the Rapanos plurality's formulation, but it did not go so far as to independently define "relatively permanent" to require standing or continuously flowing water every day of the year. The Supplemental Proposed Rule acknowledges that ambiguity but would resolve it in favor of a perennial-flow standard, reasoning that "'relatively' cannot stretch the meaning of 'permanent' to the point that 'permanent' would encompass flow for significantly less than the majority of the time."

In doing so, the Supplemental Proposed Rule potentially goes beyond what Sackett expressly required in a few ways. First, it would equate "relatively permanent" with "perennial," effectively categorically excluding intermittent streams. Second, it would introduce a 30-day bright-line threshold for non-anomalous interruptions—a numeric limit found nowhere in Sackett, Rapanos, or elsewhere in the extended WOTUS judicial history. Third, it would limit "anomalous" drought to extreme (D3) and exceptional (D4) drought classifications under the U.S. Drought Monitor. Fourth, it would treat drought lasting more than five years as the "new normal," potentially eliminating future jurisdiction over currently perennial waters. These features reflect the Agencies' policy interpretation of Sackett rather than direct codifications of the Court's holding.

The Agencies' policy interpretations are particularly relevant under the Administrative Procedure Act (APA). Neither Sackett nor Rapanos supplies a 30-day limit for ordinary interruptions. The Supplemental Proposed Rule concedes that there are "no precise, scientifically-grounded, nationally consistent time limits" for such interruptions and explains that it selected 30 days because the period "roughly" corresponds to a month and is "predictable, transparent, and easy to administer." The Supplemental Proposed Rule also acknowledges that the proposed five-year drought limit tracks the five-year expiration period for approved jurisdictional determinations outlined in the Corps' Regulatory Guidance Letter 05-02. The Agencies reason, though, that the 30-day and five-year timeframes are being proposed because they are easily administrable. However, the Agencies also acknowledge that commenters have objected to time-based thresholds as being artificial and not accounting for regional variability. There remains a significant risk that the Agencies' use of such bright-line time-based rules could be challenged in court as arbitrary and capricious under the APA without an adequate basis in the CWA or Supreme Court interpretations. Given these known objections, if adopted, the Supplemental Proposed Rule would almost certainly be subject to continuing litigation.

The Agencies' policy choices likely create vulnerabilities: the perennial-only standard may narrow what Sackett requires, while the 30-day and five-year thresholds may be arbitrary numerical limits lacking scientific foundation or adequate reasoned explanation.

What the Supplemental Proposed Rule Would Not Change

The Supplemental Proposed Rule would be limited in scope. It would not modify the proposed changes to the "interstate waters" and "lakes-and-ponds" categories. It also would leave unchanged proposed exclusions for waste treatment systems, prior converted cropland, certain ditches, and groundwater, and the definitions of "ditch," "prior converted cropland," "tributary," or "waste treatment system." The Agencies will continue to consider each of those proposals through the original NPRM.

Practical Implications

The Agencies characterize the Supplemental Proposed Rule as an Executive Order 14192 deregulatory action and state that they anticipate that the supplemental definitions will significantly reduce federal jurisdiction over streams and wetlands relative to the 2023 WOTUS rule, with the greatest effects in the arid West. The practical effect of the Supplemental Proposed Rule, if it becomes final, is that the Section 404 program is likely to see fewer permits and less required mitigation.

In practice, the proposed perennial-only standard would make the flow history of nearby waters central to any Section 404 analysis. For example, a waterbody that ordinarily lacks standing or continuously flowing water every day of the year would generally not qualify as "relatively permanent," subject to the proposed exceptions for anomalous events and a single non-anomalous interruption of up to 30 consecutive days. This would include most intermittent streams. Additionally, only the portion of wetlands with perennial surface water continuously connected to, and indistinguishably part of, a jurisdictional water would qualify as jurisdictional. If adopted, these changes could reduce federal permitting costs and timelines. However, state and local requirements could still apply.

State Regulatory Responses

The Supplemental Proposed Rule expressly recognizes that states and Tribes may regulate waters that fall outside federal CWA jurisdiction. The proposed federal narrowing may ultimately shift compliance work rather than eliminate it: state or Tribal permits, mitigation, and water-quality requirements would still apply and could, in fact, become more onerous to fill the gap left by the federal retrenchment.

For example, in California, the State Water Resources Control Board adopted its own definition of "waters of the state" that is not limited to perennial surface waters, does not require wetlands to have a continuous surface-water connection to another jurisdictional water, includes groundwater, and may encompass certain artificial wetlands.[1] Additionally,  the Washington Department of Ecology is currently conducting rulemaking (under WAC 173-217 et seq.) to establish a formal State Waters Alteration Permit program to regulate dredge-and-fill and other impacts to waters of the state that are no longer covered by the federal CWA jurisdiction post-Sackett.

Due Diligence Considerations for Transactions

For now, buyers', lenders', and investors' due diligence should distinguish existing law from the NPRM and Supplemental Proposed Rule. Environmental review should identify intermittent streams, perennial waters, wetlands, and potential surface connections; evaluate current federal, state, and Tribal requirements; and assess whether the Supplemental Proposed Rule could affect development potential, mitigation exposure, or environmental liability if adopted.

The Supplemental Proposed Rule is silent on the transitional treatment of existing approved jurisdictional determinations (AJDs), preliminary jurisdictional determinations (PJDs), pending permit applications, or existing mitigation commitments. In other words, the Supplemental Proposed Rule does not state whether, if it becomes final, pending applications would be processed under the new framework, whether prior jurisdictional determinations would retain effect, and how existing mitigation obligations would be treated. Stakeholders with pending applications or existing AJDs should evaluate whether—if the NPRM and Supplemental Proposed Rule become final—withdrawal and resubmission could be beneficial, while recognizing the associated timing, cost, and permit-risk implications. Any such strategy should be considered while monitoring the Agencies' responses to comments and any transition guidance included in the final rule.

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Molly Barker is counsel in DWT's Seattle office, Dan Quinley is counsel in the firm's San Francisco office, and Madeline Marcellino is an associate in our Portland office. For any questions, please reach out to the authors or another member of our energy, natural resources & environmental or land use teams. To stay informed, sign up for our alerts.