Swimmers were chased by a poisoned sea lion near San Francisco Bay this month

A California sea lion chased a small group of open-water swimmers back to shore near the Albany Bulb, on the eastern edge of San Francisco Bay, on September 5, 2026, in an encounter local swimmers described as unlike anything they had experienced on that stretch of water before. The animal involved, a sea lion regulars have nicknamed Blondie, has become familiar enough along that shoreline that its behavior this month stood out as a clear break from the ordinary curiosity sea lions usually show toward swimmers.

The chase coincided with a surge in domoic acid poisoning among California sea lions along the coast this year, a neurotoxin that can leave otherwise cautious animals disoriented and unusually aggressive. One open-water swimmer described the encounter as an attack, saying the group was not bitten but that it felt like one.

The Albany Bulb Encounter Happened in Daylight, Close to Shore

The swimmers involved were on a routine open-water swim, not far from shore, when the sea lion began following and bumping toward them rather than keeping its usual distance. Accounts of the encounter, compiled by the local newsroom Richmond Side, describe a rushed swim back to the beach rather than a prolonged struggle, with no injuries reported.

Encounters like this one have become common enough this year that several Bay Area swim groups have started sharing informal warnings about specific animals and locations rather than treating each sighting as an isolated event. The Albany Bulb itself is a former landfill turned public shoreline park along the Bay Trail, popular with waders and open-water swimmers because the water there is calmer and more sheltered than the open coast, the same shelter that can also draw in a disoriented animal looking to rest.

This is not the first year a domoic acid outbreak has produced an aggressive encounter along the California coast. A 2024 bloom brought a similar incident farther south, when a surfer described being confronted by a sea lion that behaved erratically enough to draw statewide coverage at the time. What distinguishes this year’s outbreak, by the Marine Mammal Center’s own count, is not the existence of aggressive encounters but their frequency.

A Neurotoxin That Turns Curious Animals Aggressive

Domoic acid accumulates in small schooling fish such as sardines and anchovies, which sea lions eat in large quantities during blooms of the algae that produce the toxin. Once ingested, the compound attacks the brain and the heart, and can cause seizures, disorientation, and heart failure in affected animals. According to NOAA Fisheries, the current bloom is being fed by an upwelling of nutrient-laden water from deeper in the ocean, the same seasonal process that periodically fuels these outbreaks along the California coast.

A sea lion in the early stages of poisoning may look and act mostly normal. One further along may lose its usual wariness of humans entirely, which is part of what makes late-stage cases more likely to end up close to swimmers rather than staying clear of them the way a healthy animal would. Domoic acid poisoning is documented to leave lasting neurological damage in some survivors rather than only acute symptoms, which is one reason a sea lion that behaves aggressively once may keep doing so on later encounters rather than returning to normal.

The Rescue Numbers Are Running Far Above Normal

The Marine Mammal Center said its team has responded to an unusually high number of California sea lions suffering domoic acid poisoning this year, with more than 150 rescued since the start of January and more than 110 of those since July 1 alone. The organization has said it typically handles somewhere between 70 and 90 domoic acid cases in an ordinary year, a figure this year’s total has already run well past.

Monterey and Santa Cruz counties have been hit hardest overall, but the Albany Bulb encounter shows the same toxin reaching animals well up into San Francisco Bay itself, not just the more exposed open coastline to the south.

A Bloom Cycle That Keeps Recurring Along the Coast

The organism responsible, a type of algae in the genus Pseudo-nitzschia, blooms when ocean conditions bring nutrient-rich water toward the surface, and warmer, more variable coastal conditions in recent years have made large blooms more frequent rather than rarer. Each bloom cycle works its way up the food chain from plankton to the small fish that sea lions depend on, which is why poisoning cases tend to spike weeks after a bloom rather than during it.

Marine mammal responders have not said when this year’s bloom is expected to taper off, and rescue totals were still climbing as of the most recent count, leaving open how many more encounters like the one near Albany Bulb are still ahead this fall.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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