Two months after the worst algal bloom in decades began to spread across the San Francisco Bay and eventually killed countless fish, ecologists and water officials are still trying to determine exactly what caused it and how to prevent such a devastating event in the future .
“I don’t think we’ll ever really know what actually triggered it,” said Erin White, executive director of the San Francisco Bay Area Water Quality Control Board, which called for additional monitoring after flowering officially ends. However, this week’s warm weather has her worried that another warmer day could be preceded by cooler weather and shorter days, as there is less sunlight to trigger the blooms.
“Once we get past October, I’m not worried about winter,” White said.
Currently, other parts of California are at risk of algal blooms. Santa Cruz County issued a warning Thursday that the county is experiencing unusually frequent algal blooms due to warmer temperatures and low water levels. The normally clear Lake Tahoe has seen a 300 percent increase in algae over the past year, according to a UC Davis report.
Large-scale algal blooms in the San Francisco Bay began in late July, when red tides began to be noticed in the eastern part of the bay and in Lake Merritt. The algal bloom soon spread across the northern, southern and central bays, and across the San Francisco coastline, killing countless fish, eventually dying on the beaches of Mare Island and near the ferry terminal in Alameda.
Scientists say the trigger for the flowering of an organism called Heterosigma akashiwo may be linked to climate change — possibly to drought or changes in wind, sunlight or temperature. That’s likely because the weather was so calm at the time, White said, which made the bay’s normally murky water clearer and allowed sunlight to penetrate.
Once it was triggered, its growth was attributed to nutrients in the treated wastewater pumped into the bay by the region’s 37 sewage treatment plants.
White worries about blooming again next summer and how best to prepare for that possibility. That involves narrowing down the cause of blooms and figuring out ways to monitor future blooms and try to stop them before they spread, she said.
“Our goal is to have some kind of early indication next spring,” she said, adding that the board hopes to explore with wastewater treatment facilities whether they can keep the wastewater temporarily if there are signs of blooming. start to prevent it from actually taking off.
Jon Rosenfield, a senior scientist at the nonprofit San Francisco Baykeeper, said his group is pushing for tighter regulation of wastewater treatment to prevent future blooms.
Additionally, as they receive tips from the public about blooms and fish kills, Rosenfeld said Baykeeper is working with the U.S. Geological Survey and other agencies and organizations to map everything they know about blooms, Including deadly duration fishing, and when and where it moves.
According to the state Department of Fish and Wildlife, the reported number of dead fish — 10,000 yellowfin gobies plus hundreds of striped bass and white sturgeon, as well as a small number of the endangered green sturgeon — may be grossly underestimated, Rosenfield said. Say. He said the dead fish count included only carcasses that washed ashore, with a Baykeeper field worker counting 10,000 dead fish in just one portion of Lake Merritt.
“I don’t think we’re going to get anything close to counting,” he said. “Many will be washed out of Golden Gate or eaten by bacteria on the bottom of the bay.”
Rosenfeld is concerned that many endangered species in the bay, such as the small albacore tuna, are likely dead and unseen by observers.
“What will come later is the impact on various wildlife species,” he said. “What can we do to provide greater protection for species that may be hit hardest?”
Tara Duggan (she/she) is a staff writer for the San Francisco Chronicle. Email: tduggan@sfchronicle.com Twitter: @taraduggan