The Duwamish River originally meandered down its fertile valley and emptied through wetlands into Elliott Bay. The wetlands were filled with soil from Seattle's regrade and canal projects. Industries were established on the river to take advantage of its access to the sea.
Beginning in 1913, the meanders were straightened to allow deep water vessels to dock at industries and to control flooding. Lumber mills, canneries, and other manufacturing operations discharged their wastes into the fresh water that flowed to Puget Sound and the sea. Operations such as shipyards and the Boeing Company's manufacture of airplanes produced persistent waste streams including heavy metals and volatile organic compounds. Municipal sewage systems, which also received industrial wastes, contributed to the toxic brew. Laws did not begin to regulate these discharges until midway through the twentieth century.
In 1980, Congress passed the Comprehensive Environmental Response, Compensation, and Liability Act - The Superfund - (40 U.S.C. 9601 et seq.) to clean up polluted sites around the country. The Duwamish joined 48 other Superfund sites in Washington state including Seattle's Harbor Island, Tacoma's Commencement Bay, and the Hanford Nuclear Reservation in Eastern Washington.