San Mateo County’s Mussel Sampling Program
This page was last updated 11/21/23
There are currently no active shellfish advisories. On November 20th, 2023 the California Department of Public Health (CDPH) lifted its warning about sport-harvested shellfish from San Mateo County. To learn more, read CDPH’s press release.
Approximately every two weeks Environmental Health Services staff collects mussel and plankton samples along San Mateo County’s coastline as part of the State’s Mussel Sampling Program.
The mussel samples are sent to the California Department of Public Health and tested for unsafe levels of naturally occurring toxic materials known as “biotoxins.” Results are published once a month to keep the public informed on when it’s unsafe to eat mussels and other shellfish.
Why are biotoxins in shellfish dangerous?
Certain species of algae (phytoplankton) produce naturally occurring biotoxins that can become too abundant in shellfish like mussels, clams, oysters, crabs, and lobsters. Shellfish consumed with unsafe levels of biotoxins can cause paralytic shellfish poisoning and other health issues that may pose a serious threat to humans and wildlife, including death.
When is it safe to eat recreationally harvested mussels in San Mateo County?
Never assume mussels are safe to eat. While a quarantine on mussels takes effect annually from May 1st - October 31st as a safety precaution, the quarantine may become extended or take effect at any time of the year. Please call the biotoxin hotline at 1-800-553-4133 before including mussels or any shellfish on your menu.
The quarantine extends from the California-Oregon boundary south to the California-Mexico boundary and applies to all bays, inlets, and harbors.
Using Mussels as Bait
Mussels for use as bait shall be broken open at the time of taking, or prior to sale at the discretion of the enforcing agency. Mussels used as bait should be placed and sold in containers adequately labeled in large bold faced letters that are at least a half an inch in size.
Clams should be washed thoroughly and cooked. All dark parts of the clams and scallops must be discarded because biotoxin is concentrated in the dark parts if present. Only the white meat of clams and scallops should be prepared for human consumption.
For the latest quarantine and health advisory updates by the California Department of Public Health’s Marine Biotoxin Monitoring Program, please call 1-800-553-4133 or click here.