Dead fish in San Francisco Bay attributed to toxic red tide

OAKLAND, Calif. (AP) — An unprecedented red tide in the San Francisco Bay Area is killing thousands of fish and other marine life whose carcasses wash ashore, creating a foul smell that experts say could worsen during the heat wave expected this weekend.

At Oakland’s Lake Merritt, a popular spot for joggers, walkers and those looking to be in nature, crews on Wednesday began removing dead crabs, rayfish, striped bass and others fish that started piling up on its rocky shores over the weekend.

The massive fish kills at Lake Merritt and throughout the Bay Area may be due to a harmful algal bloom that has been spreading through the area since late July, said Eileen White, general manager of San Francisco Bay Regional Water Quality. Control Board.

“We normally have algal blooms during the summer. But what’s unusual about this one is its size and the fact that there are kill fish,” White said.

Most algal blooms end after about a week. But a triple-digit heat wave forecast for the holiday weekend could help the Bay Area grow even further, White said. She said reports of dead fish started coming in last week.

“It was a natural event from Mother Nature and so, we don’t know when it’s going to end,” she said.

A microorganism called Heterosigma akashiwo has formed a bloom first spotted in the Alameda Estuary, White said. It’s been in the bay all the time, but scientists are trying to figure out what caused it to spread so far and so far and for so many weeks.

They say a years-long drought has prevented standing water from flowing into the ocean, and unusually hot and sunny weather could be helping algae spread.

Jon Rosenfield, a scientist with the Baykeeper conservation group in San Francisco, said high levels of nutrients like phosphorus and nitrogen in wastewater also lead to the growth of algal blooms.

“The only lever we have to control the problem is to reduce the nutrients put into the bay by the 40 sewage treatment plants that operate around the bay,” he said.

Rosenfield said sewage treatment plants clean water of solids and bacteria, but are not designed to remove nitrogen and phosphorus.

Treating water for nutrients would cost billions of dollars, and those costs would be passed on to residents, White said. She said the water districts have been funding studies to understand the effects of nutrients in the water since people settled in the area.

“The goal is to establish the appropriate regulations based on sound science,” White said.

Experts are also trying to determine exactly what is killing the fish.

Algal blooms produce a toxin that is deadly to fish and other marine life, and as they spread, bacteria in the water begin to consume the algae. As it breaks down, it depletes the water of oxygen, leading the fish to suffocate, Rosenfield said.

“Which of these mechanisms is operating here, the toxin or the low dissolved oxygen? We just don’t know yet,” he said.

Algal blooms were reported in Contra Costa and Marin counties to the north and San Mateo County to the west. In the South Bay, chlorophyll concentrations — an indicator of algae density — measured on Aug. 10 were the highest seen in more than 40 years, White said.

In Oakland, people took to social media to post photos of some of the thousands of dead fish at Lake Merritt, where visitors began complaining about the stench.

“It doesn’t smell very good right now, so it’s a little awkward,” said Graham Webster, who jogs around the lake once or twice a week.

“But the bigger question is what happens to the lake and the bay? And what causes it? Is it our fault? Can it be repaired? ” He asked.

White said the algae is not known to be toxic to humans, but can cause skin and eye irritation. His office recommends that people and pets stay away from any water that looks reddish-brown.

Cely Aquino said she regularly visits Lake Merritt and seeing all the dead fish was sad.

“I saw a lot of dead fish, and I saw a few stingrays that were dead too. It’s quite sad,” she said. “But I think nature will take care of everything. .”

___

Rodriguez reported from San Francisco.

Copyright 2022 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed without permission.

Back To Top