California
Toxic algae in Merced County lakes
3 lakes and waterways in Merced County have harmful algal bloom reports in California's official data. The most recent entry is for San Luis Reservoir: There are no bloom reports for San Luis Reservoir in the last 30 days of California's data. The most recent was a bloom report on 21 May 2026 at Pacheco pass WB side. San Luis Reservoir and O'Neill Reservoir 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.
- Los Banos Creek Reservoir 2022
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.