Sea lions are typically not aggressive toward humans. However, these usually curious and playful marine animals have been making headlines recently for multiple attacks on people off the coast of California.
The aggression is linked to a toxic algae bloom impacting nearly 400 miles of the Southern California coast, mostly in L.A. and Santa Barbara Counties. Aggressive and erratic behavior isn’t the only way this toxic bloom can affect these animals, and sea lions aren’t the only infected animals.
Sea Lion Attacks
Recently in March 2025, two people in Southern California were attacked by an aggressive sea lion. One man was on his surfboard when the sea lion charged, bit him, and dragged him off the surfboard.
The Californian, Rj LaMendola, recounted his experience on a Facebook post. In it, he explained how the sea lion seemed “...feral, almost demonic, devoid of the curiosity or playfulness.”
A similar incident occurred when a 15-year-old was in the water taking a swim test to be a lifeguard. The sea lion approached Phoebe Beltran while she was in the water and repeatedly bit her in the arm.
Both LaMendola and Beltran are recovering from their injuries.
Read More: What Is Red Tide – and Is It Getting Worse?
Why are Sea Lions Attacking People?
It’s likely that sea lions are becoming aggressive toward people because of a toxic algae bloom. According to researchers from NOAA and the Marine Mammal Care Center in Los Angeles, a bloom of Pseudo-nitzschia is the likely culprit.
Pseudo-nitzschia produces a neurotoxin known as domoic acid. This toxin can cause animals such as sea lions to be lethargic, have seizures, act erratically, and it can lead to death. According to researchers, the 2025 bloom occurred earlier than usual.
“What is unique about this event is that this bloom is very early in the season and doesn't appear to be associated with strong winds or a thick marine layer like we have seen in the past,” said Michelle Berman Kowalewski, founder and director at the Channel Islands Cetacean Research Unit, in a statement with NOAA.
The algae blooms feed on nutrients brought on by upwelling — when winds bring nutrient-rich deep ocean water to the surface. With these nutrients, the algae can grow and spread faster. Some experts at NOAA wonder if run-off from the L.A. fires could have also led to the earlier bloom.
Other Animals That Are Impacted
As the algae blooms, it can infect fish, which are a major food source for sea lions and dolphins — the other marine animal greatly impacted by this bloom. When the sea lions and dolphins eat the fish, they become poisoned and can experience the symptoms listed above.
According to NOAA, the West Coast Marine Mammal Stranding Network partners are receiving up to 100 calls a day about infected dolphins and sea lions. Besides the sea lion attacks, other reports indicated that dolphins have been seen swimming in erratic circles in shallow water and are being stranded on beaches.
Marine experts can treat animals that have been poisoned with domoic acid, however, there are so many cases that the experts have to forgo treating all the sick and focus on who they think they can save.
“We are having to do triage on the beach as we try to identify those animals where we have the greatest chance of making a difference,” said John Warner, chief executive officer of the Marine Mammal Care Center in Los Angeles, in a statement with NOAA.
NOAA and its partners are continuing to monitor the situation and are doing their best to keep both the animals and people safe. If you happen to be at the beach and see an animal looking lethargic or acting erratically, it’s suggested you stay 50 yards or more away from it.
Read More: Algal Blooms May Have Threatened These Ancient Cities
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
Marine Mammal Care Center. What Is Domoic Acid?
NOAA. Early Bloom of Toxic Algae off Southern California Sickens Hundreds of Sea Lions and Dolphins
NOAA. Could the LA Wildfires Harm Marine Life in California?
A graduate of UW-Whitewater, Monica Cull wrote for several organizations, including one that focused on bees and the natural world, before coming to Discover Magazine. Her current work also appears on her travel blog and Common State Magazine. Her love of science came from watching PBS shows as a kid with her mom and spending too much time binging Doctor Who.
