Fish Die-off Triggered by Excessive Human Waste Nutrients in the Bay

by Morgan Cantrell

A harmful algal bloom of Heterosigma akashiwo in the San Francisco Bay caused a widespread fish die-off in August and September that impacted the Corte Madera Creek Watershed. Our community observed dead white sturgeon and striped bass along the shores of the Corte Madera Marsh Ecological Reserve and various agencies around the bay issued warnings to avoid contact with the water during the bloom.

A five-foot-long white sturgeon was among the casualties of a late-summer algal bloom in San Pablo and San Francisco bays. These fish can live for decades, feeding in the shallow edges of the bay. Photo by Morgan Cantrell

Algae blooms become harmful when they release toxins and/or consume too much of the oxygen in a body of water. This was the largest algal bloom in the SF Bay in 18 years and researchers worry that they will become more frequent.

Our wastewater effluent is contributing significant levels of nitrogen and phosphorus into the bay, creating conditions that combine with high water temperatures to cause large algal blooms like the one last summer. By finding ways to curb our pollution, we can reduce ecological damage and avoid future threats to public health.

We are advocating for more stringent wastewater treatment requirements and increased use of recycled water, two proven solutions to this challenge.
What can you do?

Call and write letters asking for the regional water board to require reduced levels of nutrient discharge from treated wastewater and fund the initiatives around the bay:
San Francisco Bay Regional Water Quality Control Board
1515 Clay Street, Suite 1400
Oakland, CA 94612
Phone: (510) 622-2300

Keep an eye out for algal blooms (patches of discolored water) and dead fish along the shores in the future. Post pictures of dead fish on the iNaturalist community science app to help scientists and agencies investigate.

Ask our water district ( to invest more heavily in recycled water.