Is the lake safe?

California

Toxic algae in San Francisco County lakes

4 lakes and waterways in San Francisco County have harmful algal bloom reports in California's official data. The most recent entry is for Lake Merced: There are no bloom reports for Lake Merced in the last 30 days of California's data. The most recent was a bloom report on 25 August 2026 at South end of lake near Daly City. Lake Merced has 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.