Waters of the United States has been a “fluid” concept for years. It defines the jurisdictional limits of the authority of the United States under the Clean Water Act (CWA). President Trump’s Feb. 28, 2017, Executive Order (EO) directing the U.S. Environmental Protection Agency (EPA) and the U.S. Army Corps of Engineers (Corps) to rescind and replace the Clean Water Rule (CWR) is the latest development to resolve the question of which surface waters and wetlands may be federally regulated and subjected to CWA permitting. Many U.S. businesses objected to the rule, so this is one action that is less controversial than others the Trump Administration has taken. This article discusses its significance.