On May 27, the EPA finalized the “Clean Water Rule” which defines the scope of waters protected by the Clean Water Act. The rule is intended to clarify and implement Supreme Court decisions interpreting  the reach of Clean Water Act provisions controlled by the phrase “waters of the United States.”

Those decisions have produced considerable confusion over what waters the EPA and the Corps of Engineers can regulate. The final rule gives the federal government an expansive jurisdiction, but is less ambiguous than the proposed rule because it relies more on distances and less on imprecise terms and descriptions. The New York Times estimates the rule will apply to about 60% of the nation’s waters.

The Clean Water Rule identifies seven different categories of “waters of the United States” (“WOTUS”): traditional navigable waters, all interstate waters (including interstate wetlands), the territorial seas, impoundments, tributaries, adjacent waters, and on a case-by-case basis, waters with a significant nexus to downstream waters. The last three categories are the most controversial and will be discussed in greater detail.

The EPA defines a ‘tributary’ as a water that contributes flow to a WOTUS and is characterized by three physical indicators: a bed, bank and ordinary high water mark. But there’s some ambiguity in how far upstream one has to look for these tributary characteristics. ‘Adjacent’ waters mean bordering, contiguous or neighboring.  ‘Neighboring’ waters include waters located within 100 feet of the ordinary high water mark of a WOTUS, or waters located within the 100 year floodplain and within 1500 feet of the ordinary high water mark of a WOTUS.

Finally, the rule includes two categories of waters if they meet a ‘significant nexus’ test on a case-by-case basis.  In the first category are waters that are not per se jurisdictional, but that many anticipate likely will always meet the test.  These include Prairie potholes, Carolina bays and Delmarva bays, Pocosins, Western vernal pools, and Texas coastal prairie wetlands. The second category includes all waters located within the 100 year floodplain and located within 4000 feet of the high water mark of a WOTUS.

The Clean Water Rule has been welcomed by environmentalists, but has drawn criticism from business interests like the American Farm Bureau Federation. Many states, including Kentucky, filed lawsuits this week challenging the Clean Water Rule.

The rule was published in the Federal Register on June 29 and will be effective on August 28.