WRIA 8's marine nearshore stretches between West Point in the City of Seattle, northward to Elliott Point in the City of Mukilteo. The marine nearshore area is generally defined as the area between the upland-aquatic interface to the lower limit of the photic zone in the aquatic environment (roughly minus 30 m or 98 ft MLLW). The nearshore environment extends landward to include coastal landforms such as coastal bluffs, the backshore, sand spits, and coastal wetlands, as well as marine riparian zones on or adjacent to any of these areas. In addition, the nearshore environment includes subestuaries such as the tidally influenced portions of stream mouths.

The nearshore environment contains a variety of habitat types, such as eelgrass meadows, kelp forests, mud and sand flats, and tidal marshes. Similar to the interactions of streams with their floodplains, marine systems undergo physical, biological, and chemical processes to create and maintain habitat. These processes relate to tidal action, wave and wind energy, sediment recruitment and transport, and upland hydrology, among others (see KCDNR 2001). As with many other areas in WRIA 8, urbanization has occurred along much of the shoreline. Residential development occurs along the majority of WRIA 8's marine shoreline, with commercial and industrial uses occurring in some locations. These developments have armored banks and removed riparian vegetation. Much of the WRIA 8 shoreline is armored to protect the railroad tracks that run along the shoreline north of Shilshole Bay. Salmon use marine nearshore areas for rearing and migration, with juveniles using shallow shoreline habitats.

Marine shoreline habitat has been degraded through urbanization. Shallow gravel habitat has been lost due to disruption of natural beach forming processes, resulting from bank armoring that restricts the recruitment of sediment from adjacent areas. In addition, bank armoring concentrates wave energy at the face of the structure, increasing erosion of beach sediments. Docks, piers and jetties also alter sediment transport dynamics. The shoreline has also lost complexity from filling of tidal marshes and backshore areas, bank armoring and removal of riparian vegetation. Aquatic and terrestrial vegetation has also been lost due to development of shorelines and runoff from urbanized areas. While riparian vegetation has been directly removed as shorelines are developed, aquatic vegetation is affected by freshwater storm drains that concentrate runoff and impact marine aquatic plants that are adapted to increased salinity levels, such as eelgrass. Runoff can also increase turbidity, reducing the ability of light to penetrate the water and making deeper areas uninhabitable for photosynthetic plants.