This week, the U.S. Environmental Protection Agency (EPA) and the Army Corps of Engineers (the Corps) announced a proposed rule to revise and narrow the definition of “waters of the United States” (WOTUS). This definition and rulemaking is one of the most contested topics in the environmental policy—this rule marks the sixth time that the WOTUS definition has been changed in the past decade, and each iteration has faced litigation, with the Supreme Court ruling most decently in 2023 in Sackett v. EPA. The Biden Administration responded to that ruling with a 2023 rule that narrowed the definition, but still faced litigation for not fully implementing the ruling. That resulted in a situation where the rule had been enjoined in the 26 states that brought litigation, and who as a result were using the pre-2015 definition of WOTUS, while the other 24 states were using the 2023 revised definition. 

These latest proposed revisions seek to harmonize the regulatory framework nationwide while narrowing the application of clean water protections. EPA Administrator Lee Zeldin has expressed the hope that the new rule will be “durable” and end the cycle of changes to the regulatory standard. Nonetheless, the agencies may still face litigation once the proposed rule is finalized. The agencies are currently seeking comments on the proposed rule, which must be submitted by January 5, 2026. 

WOTUS defines the geographic extent of the U.S. Army Corps of Engineers’ and EPA’s authority under the 1972 Clean Water Act to regulate bodies of water, streams, and wetlands, and therefore is both critically important for a wide range of actions that require CWA permits, and also—due to the changing and permeable boundaries of bodies of water—extremely difficult to precisely define. In Sackett, the Supreme Court declared that the WOTUS definition includes bodies of waters that are “relatively permanent”, e.g. oceans, lakes, rivers, and streams, as well wetlands that are adjacent to such bodies of water with a “continuous surface connection”.  

Some of the most significant changes proposed in this rule are to expand waters that are excluded from the regulation. Specifically, the proposed rule removes “interstate waters” from the WOTUS definition if they are not relatively permanent and therefore don’t otherwise meet the requirements for being WOTUS jurisdiction. The rule also proposes to exclude all ditches, including roadside ditches, from WOTUS, noting that “the regulatory status of ditches has long created confusion for farmers, ranchers, irrigation districts, municipalities, water supply and stormwater manager agencies and the transportation sector.” Per the proposed rule, ditches would be entirely excluded from waters of the U.S. as long as they have been constructed entirely in dry land, even if they have relatively permanent flow and connect to jurisdictional waters, unless they are navigable (e.g. canals).  

In terms of impact, one of the most significant changes in the proposed rule will be the requirement for wetlands to be indistinguishable from jurisdictional waters through continuous surface connection. The agencies prepared a Regulatory Impact Analysis that found that as a result of this change, 81% of wetlands that are currently on the National Wetlands Inventory will not be considered waters of the US. 

This change in the extent of protected wetlands has the potential to significantly affect transportation projects and properties. Currently agencies seeking to construct transportation projects routinely must obtain a Section 404 permit, which regulates discharge into waters of the U.S. and protects the aquatic environment of those waters. While this change in definition is unlikely to affect permitting of bridges through rivers that are “relatively permanent” and therefore will still be protected, it could have significant permitting timeline benefit for roadway and transit projects with the potential to affect projects through wetlands that may no longer be protected.  

On the other hand, wetlands provide critical flood protection benefits to roadways and other transportation assets. While roadway flooding can occur from “fluvial flooding” when water in streams or lakes overtops its banks and flood adjacent properties and wetlands, which are proposed to still be protected under this rule, more often roadway flooding occurs from “pluvial flooding” caused by heavy rainfall that exceeds the absorptive capacity of the ground. The risk of pluvial flooding can be mitigated by the absorptive capacity of ecological wetlands that are unconnected to bodies of water, and it is these types of wetlands that are proposed to no longer be jurisdictional to WOTUS. Pluvial flooding is already increasing due to the increasing frequency of intense rainfall events. To the extent that the rule leads to expanded building in formerly protected wetlands, converting such wetlands to impermeable surfaces will exacerbate such flood risks further and therefore roadway and transit operators and users may more often have to contend with flooding impacts. 

Although the proposed rule seeks to establish “bright lines” to the degree possible, the topic remains a difficult issue to delineate. For instance, one topic on which the agencies are seeking comments is on whether and how natural and man-made features (such as culverts and tunnels) should affect the jurisdictional status of upstream waters, “including whether these features can connect tributaries downstream when they convey relatively permanent flow or if they should sever downstream jurisdiction.”