Over the past decade, the definition of “waters of the United States” (WOTUS) has shifted repeatedly, creating uncertainty for permitting and project planning. Building on the Supreme Court’s Sackett v. EPA decision, the EPA and the U.S. Army Corps of Engineers (together, the agencies) announced a proposal this week to further refine which water features qualify as WOTUS by narrowing key definitions and codifying — and expanding — exclusions. The proposal would apply across all Clean Water Act (CWA) programs that rely on WOTUS, including permitting under Sections 404 and 402, water quality certifications under Section 401, and Total Maximum Daily Loads (TMDLs) for impaired waters under Section 303. The proposal is directionally deregulatory, meaning fewer waters are likely to be considered federally jurisdictional and therefore regulated. The new definition was published in the Federal Register on Thursday, marking the start of a 45-day public comment period through January 5, 2026. The public comment page can be accessed here.