San Francisco Bay marine life devastated by deadly algae bloom

  • Published on September 6th, 2022

An unprecedented, massive harmful algal bloom (HAB) stretching throughout San Francisco Bay appears to be in decline, but the State Water Resources Control Board, San Francisco Regional Water Quality Control Board and California Department of Fish and Wildlife (CDFW) are warning that depleted oxygen levels could lead to “large-scale aquatic deaths” in the days ahead.

Depleted Oxygen Levels from Harmful Algal Bloom in SF Bay Could Trigger Large-Scale Aquatic Deaths
(Oakland Public Works)

By Dan Bacher

“Better known as a ‘red tide’ since it has turned much of the Bay a reddish-brown color, the HAB was first detected in Alameda in late July and has grown to become the largest in the Bay’s recorded history,” according to a press statement from the CDFW and Water Boards this afternoon. “Already, the HAB has been responsible for the deaths of thousands of fish, including large sturgeon, sharks, striped bass, bat rays and anchovies. Although this type of HAB is not considered a health threat to humans, it is recommended that people avoid swimming until further notice. The cause of the HAB is still not known.”

“It’s very upsetting to see the scale of harm to aquatic life and we know how disturbing this has been for the public,” said Eileen White, executive officer of the San Francisco Regional Water Board. “We are doing everything possible to monitor the situation, work with other agencies and search for solutions.”

The CDFW noted, “At Lake Merritt, which is connected to San Francisco Bay, reports suggest as many as 10,000 fish died in late August, On Aug. 29, San Francisco Bay Regional Water Board staff conducted a field investigation at Lake Merritt, where very low dissolved oxygen levels were measured in the water. Water samples were collected for identification of algal species and toxins.”

Updates to this sampling event will be posted on the HAB web map.

CDFW said it will be conducting both boat and shore-based surveys next week at various locations around San Pablo and Suisun bays. The goals of these surveys will be to determine the geographic extent of the fish kill, any expansion into new areas, the species affected and the numbers of dead fish on select target species such as white and green sturgeon.

CDFW said it is also tracking reports from partners and community scientists to determine where fish mortalities are occurring. Due to the likelihood of increased fish mortalities through the weekend, CDFW is encouraging people who may be recreating on the nearby shorelines in affected areas to report sightings of dead fish through the iNaturalist smartphone app.

The water boards have worked with various agencies, including the City of Oakland, Alameda County, San Mateo County and East Bay Regional Park District, to post caution advisory signs near affected waters (e.g., Lake Merritt, the Oakland Estuary, Coyote Point, and Crown Beach) to inform the public to avoid contact with the discolored water caused by the red tide.

Jon Rosenfield, fish ecologist for the San Francisco Baykeeper, said the harmful algal bloom is caused by the Heterosigma akashiwo algae species, which is frequently found in the Bay at background levels. He said this red tide is “unprecedented in its spatial extent and duration.”

“Small, short-lived algal blooms around the Bay’s margins are not uncommon. And the southern Delta is regularly plagued by extensive blooms caused by a different species, a cyanobacteria of the genus Microcystis. But nothing of this scope has been reported before in the Bay-proper,” he said.

Regarding the number of fish that have perished to date, Rosenfield said there is no way at this time to estimate total numbers because people are just seeing a very fraction of the fish that may have died.

You can take action to tell the SFPUC (San Francisco Public Utilities Commission)  to  invest heavily in water recycling and other solutions in order to stop algae blooms and fish kills:

Damon Tighe, a citizen scientist who has been pushing the local authorities to get the aerators working on Lake Merritt to raise the oxygen level in the water, reported some good news:  “One fountain is up and running in the western wing/Glen echo drainage thanks to LMI (Lake Merritt Institute) staff.”

“We really need back up fountains for when pens are taken out for repair (monthly). Collectively we could fund this.,” he added.

On San Francisco Bay, he noted that “the professionals at SFEI (San Francisco Estuary Institute) and Baykeeper now have good data on what going on. The South Bay has dissolved oxygen that’s basically a dead zone. The surface bloom may have peaked a few days ago, but since we don’t know all the factors that’s allowed for the first bloom, we could potentially see more until the usual seasonal end of this organism in October.”

He also reported he is starting to see observations of green sturgeon showing up dead just outside the Golden Gate. “The damage to JUST the Sturgeon alone we won’t recover from for DECADES,” he concluded.

This pod cast is an excellent quick catch up on what we know about the bloom so far:

“,” another citizen scientist, observed alarming numbers of dead sturgeon on a short walk in the South Bay by the Dumbarton Bridge on Thursday.

“As soon as I got out I could smell the water,” they wrote on Facebook and  “It stinks. The foam didn’t look great either. I documented at least 44 dead sturgeon and 30 other fish, on a short 1.5 km walk.”   

For more information, you can read the following reports in the Stockton Record: and USA Today:

About the Author

Dan Bacher is an environmental journalist in Sacramento who focuses on California's water issues, a healthy environment for the salmon fishery of the Northwest, and the attempts by big agriculture and big oil to hog all the water.

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