This report summarizes existing information on water quality and other indicators of the environmental conditions of the Duwamish Estuary.  King County and other agencies have collected data on water quality, sediment chemistry, and fish/shellfish tissue in the Duwamish Estuary. These data were evaluated and summarized as a part of this assessment in order to describe current conditions, identify long-term trends, and review compliance with appropriate environmental quality standards. Data include physical parameters in the water column (temperature, dissolved oxygen, salinity, pH, and turbidity/total suspended solids), chlorophyll-a, nutrients, fecal coliform bacteria, metals, and various groups of organic compounds. Data on metals and organic compounds in sediments, benthic community structure, and shellfish tissue were also analyzed.

Results showed that bacteria concentrations and temperatures in some areas did not meet water quality standards. Dissolved oxygen and nutrient levels have improved over time.  Metals and organic compounds all met aquatic life water quality criteria.  However, polychlorinated biphenyls (PCBs) did not meet EPA water quality criteria for the protection of human health.  Sediments in the Duwamish Estuary are contaminated as the result of historic activities. EPA designated Superfund cleanup sites in the Duwamish Estuary are Harbor Island, Lockheed West, and the Lower Duwamish Waterway. Most contaminants commonly identified in water and sediments of the Duwamish Estuary are also found in resident fish and shellfish tissue. Because of elevated contaminants found in fish and shellfish tissue from the Lower Duwamish and East waterways, the Washington State Department of Health has issued fish consumption advisories for the Estuary. Monitoring of fish and shellfish tissue will occur as part of the Superfund cleanup process for these waterways.