A member of the public notified Contra Costa County animal control officials that the adult female sea lion was seen near Knightsen Elementary School, mammal center spokesman Jim Oswald said.
Animal control officers were able to guide the sea lion off the street into a fenced area at the school until volunteer responders from Sausalito's Marine Mammal Center were able to retrieve her, Oswald said.
The sea lion, who was named Na'au and had been retrieved by the mammal center on two prior occasions, was identified by an microchip in her flipper.
Na'au suffers from domoic acid poisoning, a disease contracted by animals that feed on fish that have eaten toxic algae, Oswald said. The disease is known to impact an animal's ability to navigate, which could explain why she was found beached in the far East Bay.
"We're really trying to determine how toxic the poisoning is," Oswald said. If the condition is determined to be chronic, Na'au might not be re-released into the wild.
"Veterinarians will determine the best course of action," Oswald said. Depending on her diagnosis, Na'au could be placed in an aquarium or euthanized.
The Marine Mammal Center has rescued more than 970 mammals this year, Oswald said.
"The normal yearly average is around 600," he said. "There's definitely something going on."