The Rivers and Harbors Act of 1899 was adopted to protect against hazards to and interference with navigation. It prohibited “creation of any obstruction to the navigable capacity of any of the waters of the United States” or altering or filling navigable waters (§10) and also made it unlawful “to throw, discharge, or deposit . . . any refuse matter” into navigable waters “whereby navigation shall or may be impeded or obstructed,” although the Corps of Engineers could permit such a discharge if “anchorage and navigation will not be injured thereby” (§13). For two-thirds of a century, those provisions operated as one would expect. Then came the modern environmental movement, and in short order the courts and the executive branch turned these provisions about obstruction to navigation into a water-pollution control regime. As President Nixon drily put it in issuing an executive order that created a sweeping new pollution permit program under §13, the Act’s “potential for water pollution control has only recently been recognized.” Richard Nixon, Statement on Signing Executive Order Establishing a Water Quality Enforcement Program (Dec. 23, 1970).