We could see a repeat of last summer’s “red tide” toxic algae bloom that caused a mass fish kill-off at Lake Merritt, as scientists have observed the telltale reddish-brown water at shorelines in Berkeley, Emeryville, and Albany.  

If you were in town for the lead-up to Labor Day weekend late last August and early last September, you probably remember the odd occurrence of thousands of dead fish floating in Oakland’s Lake Merritt. Their cause of death was a toxic algae bloom that was the largest such outbreak in nearly a decade, killing tens and thousands of fish throughout the San Francisco Bay, and also bleeding into the San Pablo Bay.

And we could be in for a repeat of that deadly (for fish) phenomenon this year too. KPIX reports that scientists have confirmed another “red bloom” toxic algae outbreak along East Bay shorelines in Berkeley, Emeryville, and Albany. Moreover, the Chronicle adds that there are additional unconfirmed reports of the reddish-brown waters “near the San Francisco airport and Tiburon and in San Pablo Bay.”

"It's alarming to see an algae outbreak of this size in the Bay for the second year in a row," Jon Rosenfield, science director at advocacy group San Francisco Baykeeper tells KPIX. "While it's too early to tell how this harmful algae bloom will proceed, there's not much that we can do to stop it once it has started. Prevention is the only cure."

This year’s outbreak is once again being blamed on the 37 different sewage treatment plants whose waste flows into the Bay, with high levels of nitrogen and phosphorus. Still, biologists say another toxic algae outbreak might not necessarily cause another mass fish die-off, or that it could take six to seven weeks for the algae to reach pockets where large amounts of fish live.

While it’s deadly to fish, this particular species of algae is not considered harmful to people  (though it can be harmful to dogs.) This toxic algae was at one point considered a possible culprit in the case of a couple who died mysteriously along with their baby and dog in Mariposa County in the summer of 2021, though those deaths were eventually attributed to extreme heat.

If you see any of that reddish-brown algae floating in the Bay, SF Baykeeper asks that you report any “red tide” algae sightings on their website.

Related: City of Oakland Will Incinerate the 1,200 Pounds of Dead Fish That Have Turned Up in Lake Merritt [SFist]

Image: @Oakland via Twitter