California
Toxic algae in Contra Costa County lakes
20 lakes and waterways in Contra Costa County have harmful algal bloom reports in California's official data. The most recent entry is for Discovery Bay: There are no bloom reports for Discovery Bay in the last 30 days of California's data. The most recent was a Caution advisory on 8 July 2026 at Carillo Bay. Discovery Bay, San Pablo Bay and Los Vaqueros Reservoir and 4 more have had blooms in three or more years.
Lakes with bloom history
Newest report first. Each lake has its own page with the full history and what the results mean.
Other waterbodies with a report
These have one or two reports in a single year, which isn't enough history for a page of their own yet.
- Alhambra Creek 2023
- Bear Creek 2024
- Canyon Lake Golf Course 2022
- Cypress Grove Pond 2024
- Discovery Bay Golf And Country Club 2025
- Hidden Valley Lake 2024
- Kellogg Creek 2020
- Las Trampas Creek 2026
- Mcnabney Marsh 2017
- Moorhen Marsh 2023
- New York Slough 2020
- San Joaquin-Sacramento River 2026
- San Ramon Creek 2024
Source: California State Water Resources Control Board, official data, checked 24 October 2026. For today's conditions see the California HABs Portal map. No report doesn't mean a lake is safe: most water is only tested occasionally.