Why are dead fish piling up in San Francisco Bay?

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This article is part of The state of sciencea series featuring science stories from public radio stations across the United States. This story, by Joe Fitzgerald Rodriguez, was originally published by KQED.


Dozens of dead silver fish piled on top of each other and side by side among read kelp on a beach.
Dozens of dead fish washed up on the beach. Credit: Shutterstock

Thousands of dead fish are piling up in the Bay Area.

From the concrete outer edges of Oakland’s Lake Merritt to the sandy beaches of Fort Funston in San Francisco and the cobble bars of Oyster Point in San Mateo County, fish carcasses likely poisoned by a harmful algal bloom – more commonly known as red tide – wash ashore.

It’s a mass death event the San Francisco Bay Area hasn’t seen in years, says Jon Rosenfield, senior scientist with the environmental group San Francisco Baykeeper.

“From a fish’s perspective, it’s a forest fire in the water,” he said.

According to SF Baykeeper’s tally, the number of fish dying in San Francisco Bay could easily exceed hundreds of thousands, and that, Rosenfield said, could even be a “low” estimate.

His field investigator confirmed “easily tens of thousands of dead fish” in Lake Merritt alone. But Rosenfield cautioned: ‘What you see is just a hint of what’s really going on further below the surface of the water and in places where you don’t make it to shore. So it really is an uncountable number.

It can also be harmful to humans. An algal bloom of this size can cause skin irritation and respiratory problems, and the San Francisco Bay Area Water Quality Control Board advises people to avoid swimming, kayaking or other water activities until the bloom subsides.

Alameda’s Mary Spicer, who paddles the bay with an outrigger canoe team, said some members of her team had experienced skin irritation after coming in contact with the water for the past few weeks. Spicer said she started noticing water discoloration about a month ago – then it turned to a “denser, thicker chocolate brown”.

While paddling the Oakland estuary a few weeks ago, she was heartbroken to see a young harbor seal poking its head out of the discolored water. “Just to see these sea creatures… having to live in the red, brown, dense water, it’s really disconcerting,” she said.

Hundreds of small, dead silver fish trampled in dirty sand, their scales barely glinting in the light.
Dead fish line the shore of Lake Merritt in Oakland on August 29, 2022. Credit: Beth LaBerge, KQED

The National Oceanic and Atmospheric Administration describes red tides as “nuisance algal blooms” or large colonies of algal plants that grow out of control and are sometimes rust-colored. Not all algal blooms are harmful and most are beneficial in the ocean.

However, a small percentage of algae can produce deadly blooms, and that’s what Rosenfield thinks is happening.

SF Baykeeper receives reports through its dead fish pollution hotline in Foster City, Alameda, Keller Beach in Richmond, Sausalito and Fort Baker.

“Whatever number I give you would probably be too low,” Rosenfield said.

Government officials contacted by KQED have yet to confirm a figure. But on Monday, Eileen White, chief executive of the San Francisco Bay Area Water Quality Board, described the algal bloom as “very unusual” and “much more widespread” than the blooms that the agency has followed in the past.

“And this one is causing fish to die, which is not good,” she said. “So we will continue to investigate, try to find the cause and learn from it, so hopefully we can prevent them in the future.”

Damon Tighe, who describes himself on his LinkedIn profile as an educator and naturalist who studies mycology, tweeted a photo of a pile of dead fish at Lake Merritt on Sunday.

“Massive fish are dying right now in Lake Merritt,” Tighe tweeted. “May be related to the HUGE algal bloom that has been happening on the East Bay since the beginning of the month in front of Alameda where the effluent drains.” Tighe included a link to iNaturalist, a nature app that allows users to share their observations with other scientists and naturalists.

Heterosigma akashiwo, which SF Baykeeper and the San Francisco Estuary Institute and Aquatic Science Center have been tracking since it emerged last month, is an algal bloom that could lead to mass fish kills. The aquatic science center noted that reports of fish kills began to appear around August 22, although they noted that the size of the bay makes data collection a “tremendous challenge”.

What has changed, Rosenfield said, are those reports finally coming in, along with confirmation from investigators on the ground this weekend.

The algal bloom that Rosenfield says is most likely to cause the mortality, he continued, is caused by a mix of environmental conditions, possibly exacerbated by climate change, and sewage. treated discharged from sewage treatment plants in the Bay Area. The red tide species of algae, Heterosigma, can kill fish in two ways: it can produce a fish-killing toxin, but it can also lead to low levels of dissolved oxygen in the water, which can also be mortal.

“So we don’t know what mechanism is operating here. It might be both,” Rosenfield said. But the same bloom has also caused massive fish kills in other parts of the world.

11 geese swim a few meters from a muddy shore where the remains of fish lie.
Geese pass by a shoreline filled with dead fish at Lake Merritt in Oakland on Aug. 29, 2022. Credit: Beth LaBerge, KQED

The change that spurred flowering locally, Rosenfield said, was likely a tipping point in warming waters. The solution, then, is for wastewater treatment plants to start recycling wastewater in much higher volumes than they do now.

An April 2022 report by the environmental group Pacific Institute described wastewater recycling as underutilized throughout California. The group estimates that an additional 1.8 to 2.1 million acre-feet per year of municipal wastewater is available for reuse in California.

San Francisco supervisor Aaron Peskin, an avid swimmer at the South End Rowing Club, saw the red tide himself while swimming last week, Tuesday, Wednesday and Thursday.

“My wife said I couldn’t swim in it anymore,” Peskin said. “I told him about it. It was like swimming in rust.

He also began to see the problem on the shores. His constituents have already started sending him photos of dead fish on San Francisco beaches. The Peskin district includes Fisherman’s Wharf and the Embarcadero, areas whose borders touch the water. Peskin wants to make sure these areas, and beyond, see climate action.

“Our Public Utilities Commission, which is our sewer provider, needs to come up with strategies quickly so San Francisco can do its part in reducing discharges that can exacerbate red tides,” Peskin said.

A dirty and muddy shore.  In the center of the frame, a bright white streak sits upside down with its wings and belly pointing skyward.
A dead California bat ray lies on the shore of Lake Merritt in Oakland on August 29, 2022. Credit: Beth LaBerge, KQED

Contacted over the weekend, Bill Johnson, head of the sewage and law enforcement division at the San Francisco Bay Area Water Quality Control Board, pushed back against the claim. that sewage is to blame — the jury is still out, he says.

He says the water control commission spends $2.2 million a year to fund scientists who study algal blooms to see if it is indeed caused by human sewage.

“So if the solution is to have the wastewater community spend billions and billions of dollars on nutrients, then that’s what we’re going to do,” Johnson said. “But if the underlying causes are something else and investing all that money won’t solve the problem, we need to know that before we take that step.”

Rosenfield contradicted Johnson’s statements by citing a 2020 report by James Cloern, senior scientist emeritus at the U.S. Geological Survey, which showed San Francisco Bay had “high nutrient loads, primarily from municipal wastewater,” leading to the ‘potential for high algae production. ”

Either way, understanding what’s causing algal blooms is crucial, Rosenfield said, because it’s certainly not a one-size-fits-all situation. Without preventative measures, this could be an annual event, increasing as the waters warm and decreasing as they cool.

This is already starting to scare Rosenfield, who isn’t easy to scare — he’s been senior scientist at SF Baykeeper for four years and senior scientist at the Bay Institute for nearly 11 years. What really shook him was seeing a number of white sturgeon, a rare fish that is part of a recreational fishery, appear dead on Stinson Beach. They don’t die as easily, being big armored fish.

“Seeing this sturgeon is an indicator of a much bigger problem,” he said.

Like a canary in a coal mine, but with scales.

KQED’s Lesley McClurg contributed reporting for this story.


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