This report summarizes existing information on water quality and other indicators of the environmental conditions of Elliott Bay.  King County and other agencies have collected data on water quality, sediment chemistry, benthic communities, and fish/shellfish tissue in Elliott Bay. 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 Washington State 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 exceeded water quality standards often in near-shore areas along the downtown Seattle waterfront.  Despite frequently not meeting water quality standards, concentrations in these areas have declined over the past several decades.  This decline is likely due, in part, to increased CSO control.  Water temperature exceeded water quality standards in much of Elliott Bay and may be too high for some aquatic organisms including salmon.  Dissolved oxygen does not meet water quality criteria, mostly in the fall and appears to be associated with natural phenomena.  Not enough metals or organic compound data were available to characterize the Elliott Bay water column for these parameters.  The data available showed that three high molecular weight polycyclic aromatic hydrocarbons (PAHs) exceeded EPAs human health criteria.  In sediments, mercury, PAHs, phthalates, and polychlorinated biphenyls (PCBs) are the chemicals of highest concern; limited data are available on polybrominated diphenyl ethers (PBDEs) and dioxins/furans, which are also potentially of concern because of their bioaccumulative properties. Tissue data indicate that PAHs, PCBs, and PBDEs are chemicals of highest concern for fish and shellfish.