State and county health officials are warning people not to eat mussels caught for sport along the coast, including Ventura County.
Testing has revealed elevated levels in mussels of a toxin called domoic acid, said Debra Borsos, a spokeswoman for the Ventura County Environmental Health Division.
Domoic acid is produced by sea algae, which are eaten by mussels and other shellfish. The toxin's production usually increases this time of year along the California coast, necessitating an annual mussel quarantine.
It will remain in effect through October, Borsos said.
A mild case of domoic acid poisoning mimics flu symptoms, including vomiting, diarrhea, abdominal cramps and dizziness. A severe case can cause disorientation, seizures and even death.
The quarantine, which went into effect April 23, applies to all species of mussel taken by the public along the coast, including bays, harbors and estuaries. Commercially harvested shellfish are exempt.