Toxic Algae Behind Deaths of Hundreds of Sea Lions, Dolphins


  • California’s Central Coast beaches are littered with dead dolphins and sea lions this summer.
  • Large marine mammals are suffering from the effects of currently blooming neurotoxin-producing algae.
  • The toxin causes disorientation, bulging eyes, muscle spasms, and seizures and can be fatal.

Across the beaches of the central coast of California this summer, hundreds of dead sea lions, dolphins, and other marine life are washing ashore while hundreds more are sickened, delirious, and seizing as rescue workers rush to try to save them. 

The cause: microscopic, neurotoxin-producing algae blooming off the coast, making its way through the food chain, and infecting large marine mammals with domoic acid toxicity.

Harmful algal bloom (HAB) events have been recorded in Southern California in 2002, 2006, 2007, 2017, and 2022 — but this year is different.

A sick sea lion was roped off by rescue workers

A sick sea lion was roped off by rescue workers to prevent people from approaching.

Channel Islands Marine & Wildlife Institute (CIMWI)



“I can definitely say that this is the worst outbreak that we have seen,” Sam Dover, executive director of the Channel Islands Marine and Wildlife Institute, said in an email to Insider.

He added: “We have been responding to many animals that are actively showing clinical signs and die shortly thereafter. Many beaches have animals both live and dead in various states of decomposition.”

The nonprofit Channel Islands Marine and Wildlife Institute, which has posted signs on beaches across the Central Coast warning visitors not to approach sick animals, has received more than 1,000 reports of animals in distress between June 8 through June 14, according to a report submitted to NOAA Fisheries, and continues to receive between 250 and 300 reports per day.

“It’s like the waves of a tsunami keep washing over our local beaches with even more sea lions and dolphins suffering from domoic acid,” read the update from CIMWI to NOAA Fisheries sent Tuesday.

As of June 27, the update read, CIMWI has responded to over 500 live sea lions exhibiting signs of domoic acid and over 150 dead sea lions in Santa Barbara and Ventura counties.

A warning message is written in sand to prevent people from approaching a sick sea lion on the beach.

A warning message is written in sand to prevent people from approaching a sick sea lion on the beach.

Channel Islands Marine & Wildlife Institute (CIMWI)



“There have also been over 30 live common dolphin strandings which succumbed quickly to the suspected neurotoxin. The toll for dead dolphins is up to 110. The numbers for live and dead stranded marine mammals suspected of having domoic acid rises by the hour.”

Dover told Insider that domoic acid “comes from an algae that filter feeding fish such as anchovies and sardines that the mammals then ingest. The toxin affects the brain and results in seizures and in many cases death.  The toxin is dose dependent so it just depends on how much they eat and whether it will result in mortality.”

Additional symptoms of poisoning by the toxin include lethargy, disorientation, head bobbing and weaving, bulging eyes, foaming at the mouth, and muscle spasms. Beachgoers who spot a sickened animal should keep their distance, prevent pets from approaching the creature, and report the sighting to NOAA Fisheries or organizations like CIMWI.

In typical cases, domoic acid toxicity subsides within 72 hours, and sea lions can fully recover if the toxin is eliminated from the body in urine. However, due to the massive bloom of algae containing the toxin, much of the food supply contains the contaminant, and infected creatures cannot recover on their own. 

Volunteer rescuers treat sick sea life with aggressive fluid therapy to flush out their systems, anti-seizure medication if warranted, and anti-inflammatories to decrease brain swelling associated with the neurotoxin.

Signs posted by Channel Islands Marine and Wildlife Institute warning of sick seals on the beaches of Carpinteria, California.

Signs posted by Channel Islands Marine and Wildlife Institute warning of sick seals on the beaches of Carpinteria, California.

Katherine Tangalakis-Lippert



Mortality rates with adult sea lions have been “significant,” according to CIMWI, and animals are dying despite receiving treatment. While CIMWI volunteers are still rescuing adult sea lions, the extraordinarily high number of sick animals stranded on the beaches grows daily, so rescuers are focused on treating younger animals that will have ingested less toxic fish

“We thought last year’s domoic acid event affecting Santa Barbara and Ventura was tragic,” Tuesday’s CIMWI update to NOAA Fisheries added. “This year’s event is even more horrific. Our beautiful beaches are ‘littered’ with sick, dying, and deceased sea lions and dolphins.”

While rescuers from CIMWI and other organizations continue working to help stranded sea lions, the reports of sick and dying creatures far outweigh what the volunteer organizations can manage. 

“Our team members are physically tired and emotionally drained,” CIMWI’s report added. “They are ‘working’ harder and giving more than any one person and team should have to in order to do all they can to help these animals. There are just too many animals suffering from domoic acid with this algal bloom event.”

Why is the algae bloom so big?

It’s difficult to pinpoint exactly why this algae bloom has grown so big, said Vera Trainer, the Aquatic Sciences Director at the University of Washington. 

Generally, the warmer the year, the larger the blooms, Trainer said. “We have the hottest temperature on record for the ocean at the moment. That’s a contributing factor, which is caused by human impact,” John Warner, CEO of the Marine Mammal Care Center, said in an interview with KTLA. 

Moreover, this type of algae, called Pseudo-nitzschia, acts sort of like a weed. Trainer compares it to dandelions because of how much it spreads each year, and also because it has long periods of lying low until the conditions are just right for blooming. 

So it seems that right now, the conditions in the Pacific might be the perfect storm for making sea lions sick.



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