In August, thousands of dead fish washed ashore in San Mateo County, from Foster City to Coyote Point. The reports later spread into the main San Francisco Bay past Hayward and Alameda Island, to Fort Baker in Sausalito. Crossing the Richmond-San Rafael Bridge to investigate the report near San Quentin, my polarized sunglasses showed a distinctly dark swath of water along the tideline stretching from Richmond to the Larkspur channel.