Recreational shellfish harvesting is a hobby and livelihood for some in San Mateo County, but it can pose serious health risks if not done responsibly.
Approximately every two weeks, Environmental Health Services (EHS) staff collect mussel and phytoplankton samples along San Mateo County’s coast. These samples are sent to the California Department of Public Health (CDPH) and tested for unsafe levels of biotoxins. Certain species of algae naturally produce biotoxins that can become too abundant in shellfish, like mussels. Biotoxins are dangerous and can cause paralytic shellfish poisoning (PSP) and domoic acid poisoning. Mussels are at higher risk of having these toxins present in their flesh than other shellfish because they more readily store these biotoxins.
💡 Tips for staying safe:
| ✅ Dos | 🚫 Don’ts |
| Do call the biotoxin information hotline 1-800-553-4133 for the latest quarantine and health advisory updates from CDPH. | Do not harvest mussels during the annual quarantine from May 1st – October 31st due to the dangerous levels of biotoxins present. The quarantine only applies to recreationally-harvested mussels. |
| Know the symptoms of PSP – early symptoms include tingling of the lips and tongue with progression to tingling of the fingers and toes and then loss of control of arms and legs, followed by difficulty in breathing. | Do not assume recreationally harvested mussels are safe to eat at any time of the year. The annual mussel quarantine is a safety precaution, but the quarantine may be extended or take effect at any time of the year. |
| Know the symptoms of domoic acid poisoning – symptoms include vomiting, diarrhea, nausea, and abdominal cramps within 24 hours of ingestion. More serious symptoms may develop within 48 hours including headache, dizziness, confusion, disorientation, loss of short-term memory, seizures, and breathing difficulty. | |
| If you suspect you have eaten toxic mussels, get immediate emergency medical care at a hospital or call 911. |
- 🔗 More Information
- Visit smchealth.org/shellfish for more information on the Mussel Sampling Program.
- Do you enjoy fishing in San Mateo County? Learn which fish are safe-to-eat at home from the San Francisco Bay and Pacific Ocean at smchealth.org/fishsmart
- If you swim or surf, visit smchealth.org/beaches for weekly beach monitoring updates based on bacteria samples.
San Mateo County Environmental Health Services Blog 