https://www.mercurynews.com/2023/03/29/will-this-winters-megastorms-end-the-bay-areas-toxic-algae-problem/

In recent years, thick layers of cyanobacteria—commonly known as blue-green algae—have closed popular local swimming spots Lake Anza and Lake Temescal for weeks at a time.

Last summer, a toxic algae bloom in the San Francisco Bay killed thousands of fish.