Key Points

• The U.S. EPA and the U.S. Army Corps of Engineers released a joint proposal updating the definition of “Waters of the United States,” which will be open for public comment after its official publishing in the Federal Register.
• The proposed rule would narrow the definition of Waters of the United States and include exclusions for determining whether waters and wetlands are subject to permitting under the federal Clean Water Act.
• While viewed as a significant deregulation that could impact sensitive environments throughout the United States, the proposed rule’s deregulatory impact in California would be more limited, given California’s broader regulation of Waters of the State under the Porter-Cologne Water Quality Control Act.

On November 17, 2025, the U.S. Environmental Protection Agency (EPA) and the U.S. Army Corps of Engineers together announced a proposed rule updating the definition of Waters of the United States (WOTUS), in another effort to align with the Supreme Court’s Sackett decision.

As we previously discussed, the WOTUS rule was revised twice under the Biden administration, once in March 2023 to update the definition prior to the Sackett decision, and again in August 2023 to conform to Sackett by eliminating the “significant nexus” test that the decision invalidated.

This most recent revision defines key terms for determining which waters are subject to the Clean Water Act, such as “relatively permanent,” “continuous surface connection,” and “tributary.” It also addresses key exclusions by adding an exclusion for groundwater and clarifying pre-existing exclusions for ditches, prior converted cropland, and waste treatment systems. The EPA published a fact sheet on its website that covers the most notable of these proposed changes.

This proposed rule’s effect, if finalized, will have less of a deregulatory effect in California than in other states, however, given California’s expanded regulation of “Waters of the State” through the Porter-Cologne Act. The Porter-Cologne Act leaves few, if any, California waters unregulated. If anything, this narrowing of the scope of WOTUS may increase regulatory complexity in California by requiring, in some instances, that regulated entities obtain a Waste Discharge Requirements permit under the Porter-Cologne Act rather than a general permit available under the Clean Water Act. Individual permits under the Porter-Cologne Act may lead to a more burdensome review process compared to permitting under sections 404 & 401 of the federal Clean Water Act. Under those provisions of the Clean Water Act, the Regional Water Quality Control Boards’ review and permitting process is more streamlined.

Once published in the Federal Register, the proposed rule will be open for public comment for 45 days. The EPA’s pre-publication notice advises that the rule will appear on the Government Printing Office’s govinfo website and on Regulations.gov in Docket No. EPA-HQ-OW-2025-0322.

Please contact the authors of this article if further information is needed on how to engage in the rulemaking process or to understand how a reduction in jurisdiction under the Clean Water Act could affect land development and permitting in California.