Is Tomales Bay safe? Toxic algae status
Marin County, California. Harmful algal bloom (blue-green algae) reports from the California State Water Resources Control Board.
Data checked 24 October 2026. California data is updated daily.
2
bloom reports since 2023
2 of 2
years with a bloom reported (2023–2024)
2
advisories recommended: 2 Caution, 0 Warning, 0 Danger
Year by year
Each box shows bloom reports logged that year, coloured by the highest advisory recommended.
Recent reports
| Date | Location | Result |
|---|---|---|
| 27 October 2024 | Dillon beach | Caution |
| 12 November 2023 | Tomales Bay State Park Tomales Beach | Caution |
What the results mean
Algae may be present. Stay away from scum and discoloured water, and keep pets and livestock from drinking it.
Toxins at higher levels. No swimming, and keep pets and children well away from the water.
High toxin levels. Stay out of the water and off the shoreline.
Dogs and toxic algae
Dogs face the greatest risk because they swallow water and lick algae off their fur. If a bloom has been reported, keep dogs out of the water and away from scum on the shore. If your dog swims in water that might have algae, rinse it with clean water straight away and call a vet if it seems unwell.
Common questions
Is Tomales Bay safe to swim in?
The most recent entry in California's published data is from 27 October 2024: caution (Dillon beach). Blooms have been recorded at Tomales Bay in 2 different years, so treat green, scummy or discoloured water with caution. For current conditions, check the California HABs Portal map and posted signs.
Source: California State Water Resources Control Board, official data. This page is independent and not affiliated with the State of California.