In 2001, King County initiated a comprehensive study of the Green-Duwamish watershed, called the Green-Duwamish Watershed Water Quality Assessment (GDWQA) Comprehensive Monitoring Program. The primary purpose of this program is to collect and analyze water quality data within the Green-Duwamish watershed and to use these data to support a variety of King County water quality planning efforts. In support of this monitoring program, Herrera Environmental Consultants, Inc. (Herrera) was retained by the County to evaluate and summarize Green-Duwamish water quality data collected from 2001 through 2003. Information from the first year of monitoring (2001-2002) was summarized by Herrera (2004). This document represents the second water quality data report and evaluates data collected during the 2003 calendar year. A water quality loadings report was also prepared that presents methods, results, and detailed analyses of the 2001-2003 data including a hydrologic data analysis, pollutant loading calculations, analysis of land use loading factors, and statistical analysis. Results from water quality monitoring conducted in the Green- Duwamish watershed prior to 2000 are presented in the Habitat Limiting Factors and Reconnaissance Assessment for Salmon Habitat report.