The purpose of this study was to examine bacterial contamination in the three study areas at a spatial resolution sufficient to identify potential areas of concern. The study is a synoptic investigation (i.e., many samples over a short time period) intended to provide information about specific pathways of bacterial contamination and in some cases can serve as a starting point for identifying specific sources. It is a survey–level analysis that provides detailed spatial information on bacteria levels in the study areas, but limited temporal information, given cost, field collection, and analytical constraints.

Results in all areas showed that CSOs are the dominant source of bacteria during storms when CSOs discharge.  Results in Lake Union/Ship Canal show that bacteria concentrations were lowest in Montlake and Portage Bay.  Concentrations were higher in south Lake Union than north Lake Union. Highest concentrations were found in Salmon Bay including during dry weather sampling when no CSOs were discharging.  The study found no evidence to suggest that house boats are a source of bacterial contamination.  In the Duwamish Estuary, the highest concentrations were found in the East Waterway including high concentrations and human source bacteria during dry weather. Concentrations were elevated from the Green River but concentrations decayed moving downstream into marine waters. Tributary creeks also discharged high bacterial concentrations into the estuary.  In Elliott Bay, flow from the Duwamish Estuary is the dominant pathway of bacteria to the Bay. Dry weather concentrations were low but human source bacteria were found at the mouth of the East Waterway.