EPA and Corps of Engineers Release Supplemental Proposed WOTUS Rule

On November 20, 2025, the Army Corps of Engineers (“Corps”) and the Environmental Protection Agency (“EPA”) released a draft updated definition of “waters of the United States” (“WOTUS”) under the Clean Water Act. Comments were due on January 5, 2026. The definition of WOTUS determines whether a wetland or non-navigable water body is subject to the jurisdiction of the EPA and Corps under the Clean Water Act. Only WOTUS is regulated under Section 404 of the Clean Water Act. The December 2025 Well Connected newsletter detailed this proposal. Since January, observers wondered when the proposed final rule would appear.

Those questions were answered in a very unusual way when, on September 9, 2026, the EPA and Corps published a supplemental notice of proposed rulemaking on the definition of WOTUS. The notice supplements but does not replace the November 2025 proposal. The supplemental proposal responds to comments on that November 2025 proposal by presenting additional, narrower regulatory options for two concepts central to jurisdiction after Sackett v. EPA: “relatively permanent” waters and a wetland’s “continuous surface connection.”

The agencies are considering the original November approach, the supplemental alternatives, and possible variations when they develop a final rule. Comments on the supplemental notice are due October 9, 2026, in Docket No. EPA-HQ-OW-2025-0322. Until a final rule becomes effective, the supplemental proposal does not itself change which waters are federally regulated.

The Key Differences

A water must, among other requirements, be “relatively permanent” and, if not navigable-in-fact itself, must have a “continuous surface connection” to navigable-in-fact waters. The supplemental proposal defines “perennial” to mean “having standing or continuously flowing water every day of the year during ordinary conditions” or, alternatively, to mean, “surface water flowing continuously year-round,” consistent with the 2020 Navigable Waters Protection Rule.

In turn, “relatively permanent” would focus on those waters that are perennial bodies of water except during anomalous events such as drought or dry spell or due to a non-anomalous event resulting in temporary interruption for no more than 30 consecutive days in any given year, such as low tide or a regularly occurring dry spell. More than one ordinary interruption, even if the combined number of dry days is fewer than 30, could prevent the water from qualifying.

The new proposal would define “continuous surface connection” 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. This language tracks the Sackett case.

Again, an exception would cover temporary interruptions in the surface water connection as the result of anomalous events such as drought or dry spell or a temporary interruption in the surface water connection lasting no more than 30 consecutive days in any given year as a result of non-anomalous events such as low tide or a regularly occurring dry spell. The prior “continuous surface connection” requirement focused on a requirement of surface water in the wetland just during the wet season. The agencies anticipate that most wetlands treated as jurisdictional adjacent wetlands under current implementation would not qualify because these wetlands lack perennial surface water.

No other changes were made to the November 2025 proposed regulations. Groundwater remains excluded from the definition of WOTUS under the proposed regulations. However, the uncertainty surrounding the United States Supreme Court ruling in County of Maui v. Hawaii Wildlife Fund (2020) remains. In that case, the Court found that deposits of pollutants into groundwater could be regulated under the Clean Water Act if the pollutants make their way to waters of the United States. Although the County of Maui does not address the definition of waters of the United States, the decision creates uncertainty with respect to federal regulation of groundwater pollution, which is traditionally left to the states.

Takeaways from the Supplemental Proposed Rule

· The supplemental proposal adds alternatives that would significantly reduce the number of wetlands and non-navigable waterways subject to Clean Water Act jurisdiction as WOTUS. Stricter requirements for “perennial,” “relatively permanent,” and “continuous surface connection” result in this much narrower jurisdiction.

· Assuming that the proposed rule is finalized, groundwater is clearly not WOTUS. The Sackett decision made that conclusion clear, and this rule would explicitly exempt groundwater from WOTUS. The supplemental proposal does not change this conclusion.

· The proposed rule provides some clarity with definitions of tributary, continuous surface connection, relatively permanent, ditch, and other key terms. Intermittent and ephemeral streams would clearly not be subject to regulation as WOTUS under the proposals.

· Although the rule makes explicit that groundwater cannot be considered WOTUS, the Maui County backdoor remains open. Litigation will now likely focus on the lack of clarity of the Maui County factors. Courts will have to determine in which situations where contaminants in groundwater make their way to WOTUS will be regulated under the Clean Water Act.

· The supplemental proposal appears to attempt to “tighten the screws” on the definitions that determine whether waters are subject to the regulatory jurisdiction of the EPA and Corps.