Guilty ‘red tide’ as fish die by the thousands

  • Dead fish and other sea life have washed ashore in the Bay Area, and experts say an unprecedented “red tide” is the most likely cause.
  • A ‘red tide’ is a harmful algal bloom – which can produce deadly toxins and/or cause a drop in oxygen in the water.
  • The total number of dead fish from the current bay bloom is unknown. A scientist estimates that more than 10,000 fish have died in Lake Merritt since August 28.

Thousands of dead fish and other marine animal carcasses wash up in the San Francisco Bay Area, creating a foul smell. Experts say an unprecedented “red tide” algal bloom is the most likely cause.

Abnormal numbers of dead crabs, bat rays, striped bass, white sturgeon and more have been spotted across the Bay Area over the past week, officials say, including at the lake Merritt from Oakland. The onset of the fish kill could go back even further, as the harmful algal bloom has been spreading since late July.

The carcasses have environmental scientists worried as they mark a devastating loss to marine life. Experts also fear the impacts could worsen during the heat wave expected this weekend, which could lead to even greater growth in harmful algal blooms.

What is a red tide? Why does he kill the fish?

While many algal blooms are beneficial to ocean life, a “red tide” is a harmful algal bloom – which can produce potent and deadly toxins and/or cause the water’s oxygen to drop below beyond the levels necessary for survival, notes the National Ocean Service. The current Bay Area bloom was formed by a microorganism called Heterosigma akashiwo.

“This species is associated with fish kills elsewhere,” Jon Rosenfield, a fisheries ecologist at the nonprofit environmental organization San Francisco Baykeeper, told The Stockton Record, which is part of the USA TODAY Network. “It’s unclear at this point whether the bloom is causing a drop in dissolved oxygen… or producing a toxin that kills the fish, or both.”

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Algal blooms are not uncommon, but Rosenfield added that the Bay Area’s current red tide is “unprecedented in its spatial extent and duration.”

“Small, short-lived algal blooms around the margins of the bay are not uncommon. … But nothing of this magnitude has been reported before in the bay proper,” he said.

When did the Bay Area’s harmful algal bloom start?

This harmful algal bloom was first spotted in the Alameda Estuary, Eileen White, general manager of the San Francisco Bay Area Water Quality Monitoring Board, told the Associated Press. White added that the bloom has spread since late July.

Seagulls sit next to dead fish in Lake Merritt in Oakland, Calif., Monday, Aug. 29, 2022.

Most algal blooms end after about a week. But a triple-digit heat wave forecast for the upcoming Labor Day weekend could boost the Bay Area’s bloom even further, White said. “We don’t know when this is going to end,” she said.

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White noted that treating water for nutrients would cost billions of dollars. Water districts are now funding studies to understand the effects of nutrients in the water since people settled in the area, she said. “The goal is to establish the appropriate regulations based on sound science.”

How many fish died?

There’s no way to know the total number of fish that have died so far, Rosenfield said, noting that people only see a fraction of affected fish wash up on the shores of the bay.

Damon Tighe, a self-proclaimed citizen scientist, is among those monitoring fish kills in Lake Merritt. On Sunday, Tighe posted a map to show the places around the lake where the fish had perished – part of a project for naturalists, biologists and more to collect sightings on iNaturalist, an Academy social network of California Science and the National Geographic Society used to share biodiversity observations around the world.

Tighe estimates that more than 10,000 fish have died since August 28.

“I have never seen such a bad event,” he told the Stockton Record. “Everything is dying; gobies, dabs, crabs, polychaete works, shrimp, everything.”

Contributor: Dan Bacher, Stockton Record. The Associated Press.

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