Poisoned and erratic sea lions are washing up on California beaches, sparking an urgent warning for the public to stay away over fears these creatures may attack.
Wildlife experts from The Marine Mammal Center revealed that the animals are suffering from a form of brain damage caused by a neurotoxin called domoic acid – the same affliction that caused ‘demonic’ behavior and attacks on people last year.
These toxins fill portions of the ocean during algae blooms, contaminating fish like sardines and anchovies that the sea lions eat. It affects parts of the brain that control memory and behavior.
Dozens of sea lions were seen over the last week of August having seizures, twitching, moving strangely and appearing lethargic or confused as they washed along the shores near the San Francisco Bay Area.
Some of the sea lions have died from domoic acid poisoning, which is also dangerous to people who eat contaminated shellfish or certain seafoods.
Michael Milstein, a spokesperson for the National Oceanic and Atmospheric Administration (NOAA), said: ‘It is a very insidious and brutal disease that occurs both during cold water years due to strong upwelling in offshore wind here along the California coast, as well as during warmer water years.’
Wildlife officials have not reported any incidents where the disoriented sea lions attacked beachgoers this year, which became a common occurrence during cases of domoic acid poisoning in 2025.
Concerningly, experts could not fully explain why incidents were spiking so late in summer, leading to more than 100 cases of sick sea lions washing up on US beaches in 2026 so far, compared to just 70 to 90 in an average year.
Wildlife experts with The Marine Mammal Center carry a sea lion believed to be infected with the neurotoxin domoic acid
Sea lions are not typically aggressive towards humans, but scientists have said many have been infected with a terrifying neurotoxin which alters behavior (Stock Image)
The Marine Mammal Center, an animal hospital based in the Bay Area, has urged the public to stay at least 150 feet away from any sea lions that appear on shore.
‘All wildlife can be unpredictable, but sick animals are particularly stressed and disoriented,’ the group said in a statement.
The hospital added that its hotline for reporting marine animals in distress has been flooded with hundreds of calls due to wildlife being affected by toxic algae blooms in the Pacific.
‘Our Dispatch team receives more than 350 calls to our hotline on their busiest days. If left untreated, domoic acid can cause marine mammals to have seizures and heart failure,’ the center revealed.
The current hotspot has been at the Monterey Peninsula and nearby Central California Coast, near Monterey and Santa Cruz counties.
Flare-ups of the toxin began to appear earlier in the summer, but Marine Mammal Center spokesperson Giancarlo Rulli said cases are now strangely picking back up near the end of the season.
‘The fact that we are about to turn the page on August into September and just the unknowns right now of how these flare-ups have kind of popped up, surged, dissipated, and then popped back up again is a real concern,’ Rulli told SFGATE.
One potential cause for the late-season sicknesses and deaths is the emergence of a record-setting El Niño, which meteorologists have confirmed is making sea-surface temperatures in the Pacific hotter than at any other point in recorded history.
Over 100 domoic acid cases have been reported in 2026. The typical year sees between 70 and 90 cases
Domoic acid toxicosis causes sea lions to become lethargic, erratic, aggressive and suffer from seizures. The condition can be fatal without treatment
NOAA has said that strong winds off California push surface water aside and pull cold, nutrient-rich water up from the deep ocean in a process called upwelling.
Those nutrients help algae grow quickly in the sunlight. This year’s warmer El Niño water then helps certain algae, including an organism called Pseudo-nitzschia, multiply into large blooms that release the toxin domoic acid.
The toxin can poison fish, shellfish, sea lions that eat them and people who eat contaminated seafood.
Although sea lions have been documented attacking people while suffering from the brain-destroying illness, being bitten by a sea lion is not a common way for humans to be infected with the toxin. Touching a sea lion also does not lead to infections.
A case of amnesic shellfish poisoning (ASP) is the likeliest way someone would become infected, mainly through eating contaminated mussels, clams, oysters, scallops, crab guts and sardines or anchovies.
Cooking or freezing seafood does not destroy the toxin and the California Department of Public Health has warned that infections can be fatal for people who consume high amounts of domoic acid.
The California coast is now home to approximately 250,000 sea lions, compared to just 1,500 in the 1920s.
Videos taken by beachgoers earlier in July captured at least one incident where multiple sea lions chased dozens of people along the shore in San Diego, but it is not known if the animals were suffering from domoic acid contamination.
‘The toxin will naturally flush from an animal’s system over time, but sea lions repeatedly exposed to the toxin will suffer longer-lasting and more serious effects,’ the Marine Mammal Center said.
