Aug 30, 2022 - News

Dead fish collect along the San Francisco Bay amid rare algae bloom

Dead fish at Lake Merritt
Dead fish at Lake Merritt. Photo: Justin Sullivan/Getty Images

Thousands of fish are dying and washing ashore around Oakland's Lake Merritt and other parts of the San Francisco Bay.

What's happening: Environmental groups believe the algae bloom — first spotted near Alameda in late July — is to blame. The Bay's water has since turned brownish-red in color.

  • SF Baykeeper says that decomposition of the algae can "deplete oxygen in shallow areas, which can result in injury to or death of fish or other wildlife."

What they're saying: "From a fish's point of view, this is a wildfire in the water," Jon Rosenfield, a senior scientist at SF Baykeeper, told KQED.

  • Around Lake Merritt, runners told the San Francisco Chronicle the stench of dead fish is overwhelming along certain stretches, while in San Francisco, Supervisor Aaron Peskin told KQED he recently stopped swimming in the Bay — something he did regularly.
  • "It was like swimming through rust," he said.

By the numbers: Across the Bay, hundreds of thousands of fish could be dying, with tens of thousands already dead in Lake Merritt, Rosenfield estimated.

  • Still, he told KQED "it's really an uncountable number," since so many never make it to shore.

Be smart: The algae type — Heterosigma akashiwo — isn't known to be severely toxic to humans, but can cause skin irritation and respiratory problems, the Baykeeper's Rosenfield said.

  • The group has cautioned people (and their pets) from "recreating" in the Bay or eating fish, especially shellfish, that’s been caught in the area "until the algal bloom dissipates."
  • It's the first major bloom since the early 2004, and according to the Chronicle, scientists are still trying to determine the cause.

What's next: Rosenfield told Axios that heading into the fall, shorter days (with less sunlight) will help the bloom from spreading.

  • So too will colder weather, since this algae type reproduces more quickly in warmer water.
  • Still, he said, “there’s nothing we can do but wait for it to run its course” and right now, “there’s no indication that the bloom is receding.”
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