Is the lake safe?

California

Toxic algae in Tuolumne County lakes

11 lakes and waterways in Tuolumne County have harmful algal bloom reports in California's official data. The most recent entry is for Tuolumne River: There are no bloom reports for Tuolumne River in the last 30 days of California's data. The most recent was an algal mat alert sign on 12 August 2026 at NF ~0.6mi below Basin Cr. (536TMR003). Tuolumne River, Pine Mountain Lake and New Melones 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.

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.