This week, ASCE submitted comments to the U.S. Environmental Protection Agency (EPA) and U.S. Army Corps of Engineers (USACE) pertaining to the Trump Administration’s proposed rule defining “waters of the United States” (WOTUS) under the Clean Water Act. The Clean Water Act provides protections from discharges and other environmental hazards into American waterways and waterbodies which are defined as WOTUS by the two agencies. The proposed rule, which was published in the Federal Register on November 20, 2025, marks the fourth rule revising the definition of WOTUS since 2015. ASCE carefully reviewed the proposed rule and submitted comments after consulting with multiple ASCE members with expertise in water infrastructure, water resources, and natural infrastructure.
Background on WOTUS and Recent Legal Challenges
Over the past decade, WOTUS rules put forward by previous administrations have often been challenged in court, resulting in decisions narrowing the scope or in some cases striking down entirely what may be considered WOTUS under the Clean Water Act. In 2021, a federal court struck down the first Trump Administration’s finalized Navigable Waters Protection Rule, which replaced and significantly narrowed the much broader definition finalized in 2015 by the Obama Administration. In 2023, the Supreme Court ruled in Sackett v. EPA that wetlands may only be considered WOTUS if they maintain a constant surface connection to other waters of the United States, narrowing types of wetlands subject to Clean Water Act protections and forcing the Biden Administration to revise its 2023 WOTUS rule.
Key Changes in the Trump Administration’s Proposed Rule
The current Trump Administration’s proposed rule goes beyond the Sackett decision and further narrows the definition of “wetlands” to those waterbodies maintaining a continuous surface connection to relatively permanent water bodies that are continuously flowing year-round or at least during “wet seasons.” Sackett did not address water flows or define terms such as “wet season,” which ASCE noted in its comments can vary from state to state. As a result, the proposed rule would reduce the number of protected wetlands by as much as 91 percent according to one estimate.
ASCE’s Concerns About Wetlands and Flood Risk
ASCE expressed concern with this narrower definition, highlighting the importance of natural infrastructure such as wetlands and floodplains and their interconnectedness to the built environment. Wetlands absorb rainwater, helping to preserve floodplains and reducing the risk of flooding. This in turn relieves strain on stormwater infrastructure, dams, and levees, enhancing the resilience of these systems and extending their design life. ASCE noted the proposed rule goes beyond the limitations imposed under Sackett, and thereby increases the likelihood of flood risk, degrading water quality, and harming fragile ecosystems. The concerns presented by ASCE reflect Policy Statement 378- National Wetlands Regulatory Policy.
New Exclusions and Potential Interstate Conflicts
The proposed rule also included new exclusions from the definition of WOTUS. One such exclusion was that of interstate waters, which cross state borders. ASCE commented that this may create conflicts between states that share a waterbody but have differing regulatory structures governing its protection. Disputes such as this create the need for a federal role in regulating intestate waters, and the exclusion will likely result in disputes and legal challenges. The proposed rule would also explicitly exclude groundwater from the WOTUS definition. While groundwater has never been defined as WOTUS under the Clean Water Act, its exclusion raises questions about how waters that do fall under the WOTUS definition would be affected. ASCE’s comments cite the 2020 Supreme Court decision in County of Maui v. Hawaii Wildlife Fund which found that point source discharges that pass through groundwater into navigable waters are the functional equivalent of a discharge into navigable waters, requiring a federal permit. ASCE urged that EPA and USACE to examine and provide clarification on how the proposed groundwater exclusion will affect waters subject to Clean Water Act protections.
ASCE’s Next Steps and Ongoing Engagement
ASCE will continue to monitor developments with the proposed WOTUS rule in the coming weeks and months. ASCE welcomes further discussion with EPA and USACE on this critical issue.