Tomales Bay

Tomales Bay is the long, narrow Marin County estuary that sits directly on the San Andreas fault, separating the Point Reyes peninsula from the mainland. Roughly 15 miles long and barely a mile wide at its widest, it’s fed mainly by Lagunitas Creek at its head and exchanges water with the Pacific through a single mouth at Dillon Beach. The bay supports a tight, well-known cluster of oyster, clam, and mussel growers.

What we’re tracking

The Tomales portion of the project pulls together public readings from:

• Offshore buoys: sea-surface conditions and weather just outside the mouth.
• Sensors inside the bay: water temperature, salinity, and dissolved oxygen, tracked along the bay’s length.
• Tide gauges: for following tidal exchange and the layering that follows storm-driven freshwater pulses.
• Harmful-algae monitoring: weekly samples from the state’s CalHABMAP program. Tomales has been an active watch site for both Pseudo-nitzschia and Alexandrium, the genera most often responsible for shellfish-toxin events.
• River-flow gauges: Lagunitas Creek and Walker Creek, the dominant freshwater inputs that drive winter and spring saltiness changes in the bay.

The map below shows every public station feeding the project, plus an optional layer for the locations of the bay’s shellfish farms.

What comes next

Live readings and alerts are on the roadmap. For now, this page is about what’s being collected and why.