The federal Environmental Protection Agency (EPA) announced this month a proposed rule to revise the definition of “waters of the United States” (WOTUS) under the Clean Water Act. The revised rule is intended to increase predictability and stability in water pollution enforcement.

The proposed rule would narrow the definition of primary WOTUS to include only waters within the standard meaning of the term (e.g. oceans, streams, rivers, lakes, ponds, and wetlands). The proposed rule clarifies that tributaries are only protected by the Clean Water Act if they flow directly (or indirectly through other tributaries) and perennially or intermittently downstream to primary WOTUS. The proposed rule also narrows protected adjacent wetlands to wetlands with a direct hydrological surface connection to other WOTUS. The proposed rule excludes groundwater, wastewater treatment systems, most artificially created waters and ditches, and waters that flow only in response to precipitation, among other provisions.

Since the Clean Water Act was originally enacted, there has been ambiguity as to what waters are in the federal government’s jurisdiction. A 2015 EPA rule change under the Clean Water Act significantly expanded the definition of WOTUS to include tributaries that flow directly or indirectly to a traditional navigable water; waters adjacent to primary waters or tributaries, including a wide range of waters within or near the ordinary high-water mark or floodplain or some jurisdictional waters, even if they are not directly connected to primary waters. The 2015 WOTUS definition also included waters that have significant chemical, physical, or biological effects on a primary water. The 2015 rule excluded certain ditches, some artificial bodies of water and groundwater.

After the publication of the 2015 rule, 31 states, including Wisconsin, challenged the EPA’s authority to enforce the broad rule. The U.S. Supreme Court ruled in early 2018 that the 2015 rule is subject to direct review in federal district courts. Since then, district courts have issued preliminary injunctions applying to 28 states overall, including Wisconsin.

In February 2017, President Donald Trump issued an Executive Order asking EPA to revise the 2015 rule so that the Clean Water Act promotes economic growth and minimizes regulatory uncertainty, while still reducing water pollution.