Evolution of the Meaning of 'Waters of the United States' in the Clean Water Act [Updated March 5, 2019] [open pdf - 1MB]
From the Document: "For more than forty-five years, all three branches of government have struggled with how to interpret the meaning of 'waters of the United States' in the Clean Water Act. In a shift from early water pollution legislation, the 1972 amendments to the Federal Water Pollution Control Act, which came to be known as the Clean Water Act, eliminated the requirement that federally regulated waters must be capable of being used by vessels in interstate commerce. Rather than use traditional navigability tests, the 1972 amendments redefined 'navigable waters' for purposes of the Clean Water Act's jurisdiction to include 'the waters of the United States, including the territorial seas.' Disputes over the proper meaning of that phrase have been ongoing since that change."
CRS Report for Congress, R44585
Congressional Research Service: https://crsreports.congress.gov/