The purpose of this quarantine is to protect the public from deadly poisons that may be present in bivalve mollusks, such as mussels, clams, oysters and scallops. Since 1903, 582 total cases including 543 illnesses and 39 deaths have been attributed to Paralytic Shellfish Poisoning in California.

Mussels are the most dangerous because they accumulate high levels of toxins more quickly than other mollusks and are commonly eaten without removing the digestive organs. All dark meat should be removed from clams, oysters and scallops before eating, since the poison may be concentrated in those areas. Health officials emphasize that toxic mussels cannot be distinguished from harmless ones. Moreover, cooking does not destroy the toxins, as they are heat resistant.

The California quarantine applies only to mussels collected locally by sports harvesters. All commercial shellfish harvesters in California must be certified by the State and are subject to strict testing requirements.

The safest guideline to follow is: Do not eat mussels from California coastal waters collected by sports harvesters from May 1 through October 31.