LOS ANGELES -- A bloom of ocean algae that produces a toxic acid has sickened and killed hundreds of birds, sea lions and dolphins in California, environmentalists said.

Birds and animals have been washing up on shores from San Diego to San Francisco Bay.

In the past week, 40 birds have been taken to the International Bird Rescue Center in San Pedro with symptoms of domoic acid poisoning, which attacks the brain and can cause seizures.

In previous seasons, the center might see seven birds a week, director Jay Holcomb said.

"I have been doing this work for 35 years and I have never seen anything like this as far as the number of species affected, other than an oil spill," Holcomb said Thursday.

Domoic acid is produced by microscopic algae. Birds and sea mammals ingest the acid by eating fish and shellfish who dine on the algae.

The algae population increases or "blooms" every year as the ocean waters warm but this year's bloom seems early, extensive and "very, very thick," said David Caron, who teaches in the biological sciences department at University of Southern California.

"In five years of study I have not seen a bloom this large at this particular time of year," Caron said. "It's having an extraordinary impact on pelicans and many other species."

"There are conceivably thousands of animals being affected," Caron said.

The Wetland and Wildlife Care Center in Huntington Beach had received 73 sick or dead birds since Sunday, assistant director Lisa Birkle said.

The toxin has been swifter and deadlier than usual, she said.

"The concentration of the toxin is so great this year that we haven't had a chance to react to it," Birkle said. "Normally we're able to flush out the toxin with a treatment regimen ... This year they're just coming in dead."

Fourteen sea lions have been treated for domoic acid poisoning at the Pacific Marine Mammal Center in Laguna Beach. Seven died, said Michele Hunter, the center's director.

Humans can't be harmed by swimming in algae blooms but consuming fish and shellfish tainted with the acid can cause nausea, seizures and even death.

The state Department of Health Services issued a warning against eating sport-harvested shellfish, anchovies, sardines, and both sports-harvested and commercially caught lobsters and crabs.

The warning came early this year. The advisory usually runs from May 1 to Oct. 31.

A domoic outbreak in 2002 and 2003 sickened or killed more than a thousand sea lions and 50 dolphins, said Joe Cordaro, a biologist with the National Marine Fisheries Services.