Tomales Bay, located along the San Andreas Fault on California’s Marin County coast, is a long, narrow tidal estuary spanning about 15 miles (24 km) and averaging 1 mile (1.6 km) in width. This unique coastal system connects to the Pacific Ocean at its northern end and is influenced by tidal exchange, freshwater inflows, and seasonal climate patterns.

With a Mediterranean coastal climate-cool, foggy summers and mild, rainy winters-Tomales Bay supports diverse habitats, including eelgrass beds, salt marshes, and mudflats. These ecosystems provide critical feeding and nursery grounds for fish, shellfish, and migratory birds along the Pacific Flyway. The estuary is also home to thriving oyster farms, which rely on the bay’s nutrient-rich waters.

Tomales Bay plays a key role in studying coastal hydrodynamics, sediment transport, and climate change impacts, as rising sea levels and watershed changes continue to shape its ecology. Protected within Point Reyes National Seashore, the estuary remains an important site for research, recreation, and conservation.