The legal scope of “waters of the United States” has been debated in the legislature, federal agencies, and courtrooms across the country since the 1972 Clean Water Act (CWA). CWA section 404 prohibited discharge of dredged or fill material into “navigable waters” of the United States. 33 U.S.C.A. § 1344., i.e. “waters of the United States, including the territorial seas”; 33 U.S.C.A. § 1362(7), but “waters of the United States” (WOTUS) was not further defined in the CWA. Below, we review the case law and regulatory rules interpreting WOTUS, including the 1993 WOTUS definition, the 2015 “Obama Rule,” the 2019 “Trump Rule,” and the current still-unsettled status of the law.