On January 23, 2020, the U.S. Environmental Protection Agency (EPA) and the U.S. Army Corps of Engineers (Corps) issued a prepublication version of their much-anticipated final rule (Final Rule) redefining the scope of waters subject to federal jurisdiction under the Clean Water Act (to be known as the “Navigable Waters Protection Rule
”). What constitutes a “water of the United States” for purposes of Clean Water Act jurisdiction has been hotly contested since the Act was amended in the 1970s, as exemplified by the U.S. Supreme Court’s fractured and confusing 2006 decision in Rapanos v. United States
. The 2020 Final Rule, when it becomes effective, will replace the “Step One” rule
, issued by EPA and the Corps in October 2018. The Step One rule itself repealed the Obama administration’s controversial 2015 “Definition of ‘Waters of the United States’” rulemaking (2015 Rule) and reinstituted regulations originally issued in 1986.