Dead fish washing up in Lake Merritt and parts of bay

OAKLAND, Calif. - Dead fish are showing up in various parts of the Bay Area. It’s an unusual problem with no definitive answer yet, but experts believe it’s due to an algal bloom happening throughout parts of the Bay.

One area where people reported seeing dead fish is Lake Merritt in Oakland, especially near the amphitheater. It’s a sight that locals say they've never seen before.

"There’s a lot of dead fish around the edge of the lake right now.  Tiny little silver fish, brown fish," Lee Aurich said on Sunday.

A couple of weeks ago, the water at the lake began turning various hues of red to brown due to a harmful algal bloom.

And the dead fish aren’t just being found at Lake Merritt.  

San Francisco Baykeeper has photos of dead sturgeon at Oyster Point in San Mateo County, and video of more small, dead fish at the Oakland Yacht Club in Alameda. 

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The non-profit group says it has reports of dead fish in the middle of the bay between the Dumbarton and San Mateo Bridges, and along several shorelines including Foster City, Hayward, Sausalito and beyond. So, their scientist began investigating.

"The conclusion was that this was an outbreak of an organism called Heterosigma akashiwo. More commonly known as a red tide of harmful algae. Or it's a kind of red tide harmful algae," said Jon Rosenfield of San Francisco Baykeeper.

Scientists say they won’t know conclusively until they perform additional testing on the water and wildlife.

The problem is not killing all species. Some bat rays appear to be showing up in greater numbers at Lake Merritt.

"Historically, maybe one or two would be reported a month, but nothing like this," Aurich said. 

Rosenfield said not all wildlife will be impacted the same.

"I mean this is like a forest fire in the water from a fish’s perspective and, you know, all of us know now from watching wildfires in California, you know they can burn one neighborhood and leave one house untouched."

Experts say this algal bloom is happening because the bay is chronically enriched with excessive nutrients like nitrogen and phosphorus that come from forty wastewater treatment plants around the bay. What they don’t know is exactly why it’s happening now.

"So, it's been a mystery to researchers why we haven't gotten algal blooms of this scope. 

Four other estuaries in the world with even lower levels of nutrients have had chronic problems with harmful algal blooms. 

"So the question is why haven't we?" said Rosenfield.

That’s a question that will require further study.

Experts say the harmful blooms in the Bay Area will eventually go away, once the days get shorter and the air and water temperature gets cooler.

In the meantime, health experts say it’s best that people and pets stay out of the water in areas where this is a problem.