The toxin, domoic acid, is produced by a naturally occurring algae that blooms in coastal waters. But this spring, there's more of it in more places than ever before.
CBS News Correspondent Jerry Bowen reports an unprecedented rescue effort has been launched in response.
Sea lions are brought at the San Pedro marine mammal center on I.V. drips to help them get through seizures. In San Diego, they're seeing four times the number of stricken sea lions they do during a normal year. At Sea World, the medical center operating room has been converted to a nursery for pups whose mothers are too sick to nurse them.
Dr. Judy St. Leger, a Sea World veterinarian, runs a sea lion triage. She's caring for 80 animals in various stages of poisoning by the toxin, which attacks the brain.
She said it is not uncommon for the animals to appear as if they are in a coma.
The toxin is dangerous to humans, too. In 1987, three people died and 104 others fell ill on Prince Edward Island, Canada after eating tainted blue mussels.
According to Greg Langlois of the California Department of Health Services, "It's a very nasty toxin. It can affect people very severely."
Coastal waters are being tested and commercial catches like crabs and sardines are being inspected. Officials say they're safe, but warnings are out on sport caught fish and shellfish.
Meanwhile, sea lions are being given MRIs to see the extent of the brain damage and to determine which ones will survive. Most of the treated sea lions are making it, and making the leap back to the water world that's been so deadly this spring.