It has now been more than 45 years since Congress decided to regulate the “waters of the United States” in the Clean Water Act without defining the term. Those left to fill in the void are getting understandably cranky. “Waters of the United States,” or “WOTUS,” is the term of art that governs the scope of the act. Most obviously, a typical industrial facility cannot discharge its treated wastewater (i.e., pollutants) into a river without first obtaining a permit from the U.S. Environmental Protection Agency (EPA) or a state or tribal authority with delegated authority.