The scope of federal jurisdiction under the Clean Water Act is about to change again, and this round of rulemaking is one that landowners, developers, and energy and infrastructure sponsors cannot afford to watch from the sidelines. On November 20, 2025, the U.S. Environmental Protection Agency (EPA) and the U.S. Army Corps of Engineers (Corps) (together, the agencies) published a proposed rule that would substantially narrow the definition of “waters of the United States” (WOTUS) under the Clean Water Act, and on September 4, 2026, the agencies issued a supplemental notice seeking additional comment on two of the proposal’s most consequential definitions. Together, these actions signal that a new, narrower WOTUS rule is likely to take effect within the next year, and developers and landowners should be evaluating how the changes will affect their sites.

Why This Rulemaking Matters

The WOTUS rules determine when federal Clean Water Act Section 404 dredge-and-fill permit coverage is required, driving timelines, mitigation costs, and litigation exposure for nearly every land-disturbing project, including solar and wind installations, transmission and pipeline corridors, battery storage sites, mining operations, data centers, and conventional real estate development. Getting the jurisdictional determination wrong can mean an unpermitted discharge and enforcement risk, or an unnecessary and costly 404 permit and mitigation obligation that a project did not need.

The proposed 2026 rule follows directly from the Supreme Court’s 2023 decision in Sackett v. EPA, which held that the Clean Water Act’s use of “waters” reaches only relatively permanent, standing or continuously flowing bodies of water connected to traditional navigable waters, and that adjacent wetlands are jurisdictional only where they have a continuous surface connection making it difficult to determine where the water ends and the wetland begins. The agencies now allege that their 2023 rule implementing Sackett did not go far enough, and the current proposal is a considerably more restrictive rewrite intended to be the “durable” final rule.

The Headline Changes in the November 2025 Proposal

The November 2025 proposal would substantially narrow WOTUS by removing a standalone jurisdictional category, defining “relatively permanent” for the first time (using a regional “wet season” standard), requiring tributaries to have a bed and banks with flow, limiting adjacent-wetland jurisdiction to areas with both physical abutment and wet-season surface water, tightening the exclusions for waste treatment systems, prior converted cropland, and ditches, and expressly excluding groundwater from the definition of WOTUS. Interstate waters were also removed as a standalone category. The proposal eliminates interstate waters as an independent basis for jurisdiction, meaning such waters would only be regulated if they independently qualify as traditional navigable waters, relatively permanent tributaries, jurisdictional impoundments, or adjacent wetlands.

The Agencies Are Not Done: The September 2026 Supplemental Notice

After receiving approximately 220,000 comments on the November 2025 proposal, the agencies announced on September 4, 2026, that they would delay finalizing the rule. Instead, the agencies issued a supplemental notice of proposed rulemaking that reopened comments on two key definitions. The notice responds to concerns that the original “wet season” concept would be difficult to apply, particularly in the arid West, and could conflict with the flow-duration standard endorsed by the Supreme Court in Sackett.

The supplemental notice presents a substantially narrower alternative. Under this option, “relatively permanent” waters would generally be limited to perennial waters: those with standing or continuously flowing water every day of the year under ordinary conditions. Two narrow exceptions would apply: (1) a temporary interruption of no more than thirty consecutive days per year caused by a non-anomalous event, such as low tide or a recurring dry spell; and (2) an interruption of any duration caused by an anomalous event, such as drought, provided the drought does not last more than five years. After five years, the dry condition would become the new baseline, and the water would lose jurisdictional status. The definition of a wetland’s “continuous surface connection” would be revised similarly to require a perennial surface-water connection to jurisdictional waters, subject to the same drought and dry-spell exceptions.

If adopted, this supplemental approach would be considerably narrower than even the November 2025 proposal. Streams and wetlands that flow or hold water for a substantial part of the year but dry up on a recurring seasonal basis for more than thirty days, a pattern common west of the Mississippi and in many arid and semi-arid regions, would likely fall outside federal jurisdiction. Comments on the supplemental notice are due by October 9, 2026.

What This Means in Practice

1. Jurisdictional determinations can be a bit of a moving target. Any approved or preliminary jurisdictional determination obtained under the current Amended 2023 Rule may not reflect how a site will be regulated once a final rule takes effect, and jurisdictional determinations are generally only valid for five years in any event.
2. Arid and seasonal-flow regions face the most uncertainty. Developers with projects in the arid West, or anywhere with pronounced wet and dry seasons, should pay close attention to which version of “relatively permanent” and “continuous surface connection” the agencies ultimately adopt, since the difference between the November 2025 proposal and the September 2026 supplemental option could determine whether Section 404 permit coverage is required.
3. Deregulation at the federal level does not mean deregulation at the state level. The agencies have been explicit that waters falling outside federal jurisdiction remain subject to state, Tribal, and local regulation. Project teams need to confirm state-law coverage in every jurisdiction where a site is located, since some states regulate waters more broadly than the federal government will under any version of this rule.
4. Permitting strategy and timing deserve a fresh look. Projects currently in the jurisdictional determination or permitting pipeline may benefit from timing decisions around the rulemaking process, and project teams should reassess mitigation budgets, easement and wetland delineation scopes, and construction schedules considering a definition that is very likely to shift again.

The Bottom Line

This is the sixth regulatory attempt in roughly a decade to define WOTUS, and the issue will remain unsettled until a final rule is published—and likely litigated. Meanwhile, the range of possible outcomes, from the November 2025 proposal to the more restrictive September 2026 supplemental option, is broad enough that landowners, developers, and energy and infrastructure sponsors should assess their exposure now. Whether scoping a new project, relying on an existing jurisdictional determination, or considering comments on the supplemental notice, project teams should reevaluate which waters on their sites may be federally regulated.

For more information about how the proposed and supplemental WOTUS rules could affect your project, or to discuss commenting on the September 2026 supplemental notice, please contact Jon Micah Goeller at jonmicah.goeller@huschblackwell.com.