This report summarizes the biological data collected during a 5-year research project, titled 'An Environmental Assessment of Northern Puget Sound and the Strait of Juan de Fuca.' This report also incorporates biological data collected during a similar program conducted by the Washington Department of Ecology, titled 'North Puget Sound Baseline Study.' The report provides an overview of the geography, geology, oceanography, and habitat characteristics of the study area. Summarized information on food webs, biological communities, migrations, reproductive processes, and natural stresses is provided. Major habitat types are defined and characterized by physical and biological parameters. Descriptions are provided for the structures of biological communities associated with each major habitat type; major trophic interactions; trends in organism density, community biomass and species richness.