Wildlife officials are warning the public of a toxic algae bloom affecting marine mammals along Los Angeles County beaches.

On Monday evening, the city of Hermosa Beach posted an “Urgent Marine Wildlife Alert” message to X, telling beachgoers to keep 50 feet away from any stranded marine mammals.

This warning comes after months of sea lions, dolphins and other mammals stranding themselves ashore – suffering from domoic acid poisoning.

According to experts, domoic acid is a naturally occurring toxin in algae that is potentially lethal to marine mammals like sea lions and dolphins.

The Channel Islands Marina and Wildlife Institute (CIMWI) said warmer water temperatures, increased sunlight exposure and increased nutrients within coastal ecosystems contribute to the toxic algae bloom.

“When filter-feeders (e.g., small fish, shellfish, and bivalves) consume the toxic algae, they are not affected,” explained CIMWI. “But when predators like sea lions, sea birds, and dolphins eat these filter-feeders, they are negatively impacted by the toxin accumulated in their prey.”

In recent years, high levels of the neurotoxin have led to widespread beachings of sea lions and other marine mammals who are too sick to swim and may experience life-threatening symptoms like seizures, brain damage and unpredictable behavior.

The toxin will naturally flush out of an animal’s body, but repeated exposure may require medical intervention.

Recently, a man was arrested for beating an infected sea lion with a large stick in Ventura. Officials said it’s critically important that a sick animal be left alone to protect them and the public.

Officials said sickened sea lions can exhibit a mix of symptoms:

• stargazing (head extended backward, staring into space)
• disorientation
• head weaving
• mouth foaming
• lethargy
• erratic behavior
• inability to get out of the tidal zone
• unresponsiveness
• involuntary muscle spasms
• seizures
• side-to-side head movement

If you see a sickened sea lion or other mammal, do not approach it. Instead, observe it from at least 50 feet away, determine its exact location and report it to the CIMWI Rescue Hotline at 805-567-1505, or the Marina Mammal Care Center rescue hotling at 1-800-39-WHALE (94253).