A New Definition of WOTUS Surfaces

With passage of the federal Clean Water Act (CWA) in 1972, the U.S. finally had a landmark environmental protection law on the books to protect “navigable waters” or “waters of the United States, including the territorial seas” (WOTUS).

But the reach of a federal law depends on its supporting legal framework. In this case, the lynchpin of the CWA centers on the definition of “waters of the United States”, establishing the act’s ability to regulate different kinds of bodies of water.

Since the law’s enactment, the definition of “navigable waters” has been the source of considerable debate and decades of litigation. Regardless of whether the interpretation is broad or narrow, the definition of WOTUS impacts not just major sectors of the economy like construction, agriculture, energy production, and infrastructure development, but the activities of private property owners as well. Clearly, a solid understanding of the current definition of WOTUS is key for landowners and engineers alike. This post explores the evolving interpretation of WOTUS, recent legal developments, and implications for practicing engineers around the U.S.

A brief history of WOTUS

The waters that constitute WOTUS have undergone several interpretations over the years. From 1972 to 2015, the CWA regulated traditionally navigable waters, their tributaries, and adjacent wetlands, but agency determinations were frequently criticized. The Obama administration expanded the definition of WOTUS to encompass more types of water bodies, including intermittent streams and specific types of isolated wetlands. This broader interpretation changed during the first Trump administration; the 2020 Navigable Waters Protection Rule narrowed the scope, excluding many wetlands and ephemeral streams.

A significant development in the WOTUS saga came with the Supreme Court’s decision in Sackett v. Environmental Protection Agency (2023). This ruling rejected the “significant nexus” test previously adopted by the EPA to identify federally protected wetlands. Instead, the Sackett Court established a new standard requiring wetlands to have a “continuous surface connection” to traditional navigable waters like “streams, oceans, rivers and lakes” to be considered WOTUS. This decision effectively narrowed the scope of waters subject to federal regulation under the CWA.

Draft rules following Sackett

In response to the Sackett decision, the EPA and the U.S. Army Corps of Engineers have developed new proposed rules to align the WOTUS definition with the Court’s ruling. (The public comment period recently closed on January 5, 2026.) The proposed rules aim to provide more precise guidelines for determining what constitutes a “continuous surface connection.” The rule’s draft language suggests that this criterion will be established by “surface water at least during the wet season and abutting (i.e. touching) a jurisdictional water.” According to Sackett, protection is narrowed to “relatively permanent, standing or continuously flowing bodies of water.” The draft rules interpret this language to mean that if there is only intermittent flow during the wet season—even if water flows continuously outside of this period— a body of water will no longer have jurisdiction. The rules have not been finalized, and the language referenced above represents only a fraction of the complete text, but the implications of these proposed changes could be significant. A reduction in federally protected waters is likely, particularly in arid regions and areas with isolated wetlands.

In some states, protections can exceed the minimum set by Sackett

Prior to the Sackett decision—and in some cases, since the decision—several states have enacted into law broader interpretations of what is protected under state law, essentially restoring protection to wetlands that are now likely unprotected under federal law. California, Washington, Minnesota, New York, Wisconsin and Massachusetts represent states with more expansive definitions of protected waters. For example, California’s State Water Resources Control Board has codified an inclusive definition of “waters of the state” that asserts jurisdiction over nearly all surface waters as well as groundwater. Similarly, Washington’s Water Pollution Control Act covers a wide range of water bodies, including isolated wetlands.

The definition of WOTUS remains a politically fraught and evolving issue with obvious implications for the scope and complexity of engineering projects. Engineers and water resource managers need to navigate carefully through a complex and rapidly shifting regulatory environment. Federal oversight may be reduced in many areas, but state and local regulations can fill the gap with broader protections. The challenge lies in balancing development needs with the critical task of protecting our nation’s water resources. Hopefully the proposed rules will achieve that essential, but often elusive balance that is increasingly necessary.