In response to rapidly disappearing wetlands and its prime location within the Pacific Flyway, the refuge was created in 1974 to protect migratory birds, wetland habitat, and endangered species. The refuge and San Pablo Bay supports the largest wintering population of canvasbacks on the west coast, and protects the endangered salt marsh harvest mouse and the California clapper rail.
The San Pablo Bay National Wildlife Refuge lies along the north shore of San Pablo Bay in Sonoma, Solano, and Napa Counties in northern California. The refuge includes open bay/tidal marsh, mud flats, and seasonal and managed wetland habitats.
The Napa-Sonoma marshes in San Pablo Bay have been greatly impacted by human activities such as hydraulic mining, salt production, water diversions, and diking, draining, and filling for agricultural and industrial uses. About 85 percent of the historic tidal marshes of San Pablo Bay have been altered, negatively affecting the ability of the remaining tidal marshes to accept winter rainfall and purify water in the bay.
The refuge provides critical migratory and wintering habitat for shorebirds and waterfowl, particularly diving ducks, and provides year-round habitat for endangered, threatened, and sensitive species like the California clapper rail, salt marsh harvest mouse, California black rail, San Pablo song sparrow, and Suisun shrew.
Numerous other threatened, endangered, and sensitive species require tidal marsh habitat for their survival, including 11 fish species that swim through San Pablo Bay to reach their fresh water spawning grounds.