On November 17, 2025, the US Army Corps of Engineers (the Corps) and the US Environmental Protection Agency (EPA) released a proposed rule revising the regulatory definition of “waters of the United States,” or “WOTUS,” a key phrase in the Clean Water Act that determines the jurisdictional reach of the Act. The agencies are soliciting comments on the proposed rule, which are due 45 days from the proposed rule’s publication in the Federal Register. A pre-publication copy of the rule is available here.
The proposed rule is just the latest change in the seemingly never-ending series of changes to the WOTUS definition — changes instigated both by rulemaking and the US Supreme Court. The new proposed definition builds upon several regulatory changes implemented by the Biden administration in September 2023 to further align the WOTUS definition with the Supreme Court’s 2023 decision in Sackett v. EPA, 598 U.S. 651 (2023). Through issuance of the proposed rule, the agencies aim to “ensure clarity and predictability for Federal agencies, States, Tribes, the regulated community, and the public …”
Critical Changes to WOTUS and Related Definitions
The agencies propose defining key terms and clarifying the types of waterbodies subject to the Clean Water Act, consistent with Supreme Court precedent. The regulations currently in effect at 33 C.F.R. § 328.3 and 40 C.F.R. § 120.2 define WOTUS as waters that are used, have been used, or may be susceptible to use in interstate or foreign commerce (including all waters which are subject to the ebb and flow of the tide), the territorial seas and interstate waters. The current definition also encompasses impoundments, tributaries, wetlands, and intrastate lakes and ponds where these waters are (1) relatively permanent, standing or continuously flowing bodies of water; (2) with a continuous surface connection to waters used for interstate or foreign commerce, the territorial seas, or interstate waters.
As proposed, the revised definition would expressly exclude interstate waters and intrastate lakes and ponds from the definition of WOTUS unless those waters have the required connection to a traditional navigable water. The proposed rule also would clarify that groundwater is not a WOTUS. The rule also proposes to define several key terms, including “relatively permanent,” “continuous surface connection,” and “tributary.”
- New Exclusions. The rule proposes to exclude interstate waters and intrastate lakes or ponds unless they are otherwise jurisdictional. The agencies reason that the exclusions are needed because these categories can encompass bodies of water that do not meet the current definition of WOTUS, i.e., they are not relatively permanent, standing, or continuously flowing or are not themselves connected to a downstream traditional navigable water or the territorial seas, either directly or through one or more waters or features that convey relatively permanent flow.
- Definition of Key Terms. To provide further clarity surrounding what impoundments, tributaries, and wetlands are included in the definition of WOTUS, the agencies propose to define “relatively permanent,” “continuous surface connection,” and “tributary” as follows:
- “Relatively Permanent:” The proposed rule defines “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 agencies explain that the use of “wet season” is faithful to the plurality’s opinion in Rapanos v. United States, 547 U.S. 715, 743 (2006) and the majority’s opinion in Sackett by excluding ephemeral streams (surface waters that flow only in direct response to precipitation) but not excluding seasonal waters. Ephemeral waters were already out post-Sackett.
- “Wet Season:” While “wet season” is not a defined term in the proposed regulations, the agencies state that geographic region is a key factor in determining the length and timing of expected flow during the “wet season.” The agencies explain that “[t]he time period, including duration, constituting a ‘wet season’ varies across the country due to many relevant factors including climate, hydrology, topography, soils, and other conditions.” The proposed rule notes that the phrase “at least during the wet season” is “intended to include extended periods of predictable, continuous surface hydrology occurring in the same geographic feature year after year in response to the wet season, such as when average monthly precipitation exceeds average monthly evapotranspiration. As proposed, surface hydrology would be required to be continuous throughout the entirety of the wet season.”
- “Continuous Surface Connection:” The proposed rule defines “continuous surface connection” as “having surface water at least during the wet season and abutting (i.e., touching) a jurisdictional water.” This proposed definition provides a two-prong test that requires both (1) abutment of a jurisdictional water; and (2) having surface water at least during the wet season.
- “Tributary:” Under the proposed rule, tributary is defined as a body of water with relatively permanent flow, and a bed and banks, that connects to a downstream traditional navigable water or the territorial seas, either directly or through one or more waters or features that convey relatively permanent flow. The rule further provides that a tributary does not include a body of water that contributes surface water flow to a downstream jurisdictional water through a feature such as a channelized non-jurisdictional surface water feature, subterranean river, culvert, dam, tunnel, or similar artificial feature, or through a debris pile, boulder field, wetland, or similar natural feature, if such feature does not convey relatively permanent flow.
- Clarified Exclusions. The proposed rule provides more specific and updated definitions for certain waters that have previously been excluded from the definition of WOTUS, including ditches, prior converted cropland, and waste treatment systems.
- Ditches: The proposed rule excludes ditches entirely if they are constructed or excavated entirely in dry land from WOTUS and proposes to define a ditch as a constructed or excavated channel used to convey water, including roadside ditches.
- Groundwater: The proposed rule excludes groundwater from the definition of WOTUS, including groundwater drained through subsurface drainage systems. This change is consistent with the agencies’ past practice of determining that groundwater is not a WOTUS.
- Prior Converted Cropland: The proposed rule continues to exclude from WOTUS “prior converted cropland.”
- Waste Treatment Systems: The proposed rule continues to exclude “waste treatment systems” from WOTUS.
Request for Comment
The agencies solicit comments from the public on many specific topics during the 45-day period following the proposed rule’s publication in the Federal Register, including:
- Alternative approaches to determining the jurisdictional scope of the Act, such as an approach where WOTUS would encompass traditional navigable waters, tributaries that directly flow into these waters, and wetlands with a continuous surface water connection to such waters, with all other waters excluded.
- The definition of “relatively permanent,” specifically whether the term should be limited to perennial waters.
- The most appropriate method to identify the wet season under the proposed definition of “relatively permanent,” and whether a definition of “wet season” should be added to the regulatory text to provide clarity and transparency.
- The definition of “continuous surface connection,” specifically whether this definition and its reference of the term “wet season” would have a disproportionate impact on the arid West.
Takeaways
Overall, the proposed rule builds upon the agencies’ September 2023 rulemaking implementing Sackett by defining key terms and excluding interstate waters that do not otherwise meet the test for WOTUS as defined by the Supreme Court. The revisions proposed may give rise to additional questions of interpretation, such as what constitutes the “wet season” or how periods of drought factor into determinations of jurisdiction. Regulated entities should consider commenting on the proposed rule to ensure their input is considered by the agencies.
