California Department of Public Health press release:

The California Department of Public Health (CDPH) announced today the statewide annual quarantine on mussels gathered by sport harvesters from California’s ocean waters ends at midnight on Thursday, October 31, 2019, for all coastal counties except for Humboldt and Mendocino counties.

The annual quarantine on sport-harvested mussels, which typically runs May 1 through October 31, is intended to protect the public from shellfish poisoning caused by marine biotoxins. There have been no reports of shellfish related poisonings in California during this quarantine period.

CDPH has also lifted the September 4, 2019 shellfish safety notification related to sport-harvested whole scallops and all clams in Sonoma County. The safety notification was issued due to dangerous levels of naturally occurring paralytic shellfish poisoning (PSP) toxins that can cause illness or death. However, recent testing shows that PSP toxins have decreased to safe or undetectable levels in this area.
CDPH previously issued a safety notification warning consumers not to eat mussels, clams, or whole scallops from Humboldt and Mendocino counties: this advisory remains in effect. Dangerous levels of domoic acid have been detected in mussels from Humboldt and Mendocino counties, making them unsafe to consume. Domoic acid and PSP toxins remain at low or undetectable levels along all other portions of the California coast with the exception of razor clams in Humboldt and Del Norte counties.

These warnings do not apply to commercially sold clams, mussels, scallops or oysters from approved sources. State law permits only state-certified commercial shellfish harvesters or dealers to sell these products. Shellfish sold by certified harvesters and dealers are subject to frequent mandatory testing to monitor for toxins.

CDPH’s shellfish sampling and testing programs issue warnings or quarantines when needed. Local health departments, various state, federal and tribal agencies, community groups and others participate in the monitoring program. Residents and community groups interested in volunteering to assist with the testing program should email RedTide@cdph.ca.gov or call (800) 553-4133.

Updated information about current conditions is available by calling the Shellfish Information Line at (800) 553-4133. More information can be found on the CDPH Marine Biotoxin Monitoring Web page or the CDPH Annual Mussel Quarantine - Frequently Asked Questions (FAQ) Web page.