Supply and Demand Assessment (SDA) – Tomales-Drakes Bay

The Tomales – Drakes Bay Watershed spans approximately 220 square miles in western Marin County, with a small portion extending into Sonoma County. The watershed’s core feature, Tomales Bay, is a 12-mile-long, shallow coastal estuary less than a mile wide, bordered by the San Andreas Fault zone and fed by two primary tributaries—Lagunitas Creek and Walker Creek—along with about 20 smaller intermittent streams. Lagunitas Creek and its tributaries account for roughly 52% of the watershed’s drainage area, while Walker Creek covers about 35%. The region features a wide range of ecological zones, including redwood forests, coastal scrub, freshwater marshes, and intertidal wetlands. It supports a rich diversity of aquatic and terrestrial species, including endangered coho salmon, steelhead trout, tidewater goby, and California freshwater shrimp. Much of the watershed remains in agricultural use—particularly dairy and grazing operations—which cover more than half of the land area.

Water quality concerns in the watershed stem from nonpoint source pollution such as livestock runoff, failing septic systems, and sedimentation from unpaved roads. These have led to shellfish bed closures, swimming advisories, and elevated mercury levels in fish. The Tomales Bay Watershed Council and partners developed the Integrated Coastal Watershed Management Plan (ICWMP) to address these challenges. The plan emphasizes protecting ecological integrity, supporting mariculture and agriculture, improving water quality, and enhancing water supply reliability. Management strategies are built on collaboration among local communities, water districts, landowners, agencies, and conservation groups, all working to safeguard the watershed’s ecological and economic values.