Dozens of sea lions are washing up on California beaches, exhibiting erratic behavior and neurological distress due to a neurotoxin known as domoic acid. Wildlife experts are issuing urgent warnings for the public to maintain distance from the affected animals.
The Marine Mammal Center reported that the sea lions are suffering from brain damage caused by the toxin, which can contaminate fish such as sardines and anchovies. Domoic acid affects parts of the brain responsible for memory and behavior, leading to symptoms like seizures, twitching, lethargy, and confusion.
Over the last week of August, numerous sea lions were observed in distress along the shores near the San Francisco Bay Area. Some of these animals have died from the poisoning. The toxin is also dangerous to humans who consume contaminated shellfish or certain seafoods.
Michael Milstein, a spokesperson for the National Oceanic and Atmospheric Administration (NOAA), described the illness as "insidious and brutal," occurring during both cold and warm water years due to oceanographic conditions like strong upwelling along the California coast.
While wildlife officials have not reported any sea lion attacks on beachgoers this year, such incidents were common during previous domoic acid poisoning events in 2025. This year, more than 100 cases of sick sea lions washing ashore have been reported, exceeding the typical annual range of 70 to 90 cases.
The Marine Mammal Center has advised the public to stay at least 150 feet away from any sea lions found on shore. The organization has received hundreds of calls to its hotline reporting marine animals in distress, which it attributes to toxic algae blooms in the Pacific.
Giancarlo Rulli, a spokesperson for the Marine Mammal Center, noted a particular concern regarding the resurgence of cases near the end of the summer season, with flare-ups appearing, dissipating, and then reappearing. This pattern is unexpected so late in the season.
A potential factor contributing to the late-summer sicknesses is the current El Niño, which has led to record-high sea surface temperatures in the Pacific. NOAA explains that strong winds off California cause upwelling, bringing nutrient-rich deep water to the surface. These nutrients can fuel algae growth, and warmer El Niño waters can promote blooms of certain algae, like Pseudo-nitzschia, which produce domoic acid.
While sea lions can attack humans when disoriented by the toxin, human infection typically occurs through consumption of contaminated seafood, particularly mussels, clams, oysters, scallops, crab guts, sardines, or anchovies. Cooking or freezing seafood does not eliminate the toxin, and the California Department of Public Health warns that consuming high amounts can be fatal.
The California coast is now home to an estimated 250,000 sea lions, a significant increase from the 1,500 recorded in the 1920s. Although videos have emerged of sea lions chasing people on beaches in San Diego, it is not confirmed whether those animals were suffering from domoic acid contamination.
According to the Marine Mammal Center, the toxin will naturally flush from an animal's system over time, but repeated exposure can lead to more severe and long-lasting effects.