Additional Resources and Information

Construct a “water wand”: This can be made out of any tubing that will fit in the access hole on the well seal. ½-inch copper pipe works well. Attach a female garden hose fitting to one end of about a 4-foot section and cap or crimp the other end. Drill a series of small holes in the pipe for the water to spray out. Too many holes will prevent the wand from generating a good spray action. Test the wand before you use it. The idea is that it will thoroughly wet the inside of the well casing with chlorinated water.

1. Plan a time window with little or no water usage for a period of at least 48 hours.
2. Add white vinegar to the well water to achieve a pH between 5.5 and 6. You may be adding ½ to 1 gallon at a time between testing. Depending on water chemistry, plan on having 2 to 3 gallons on hand.
3. Once the desired pH is achieved, add chlorine solution to the well water to achieve approximately 200 ppm free chlorine. mg/L or ppm can be calculated from an estimated volume of water in the well.
4. Attach a garden hose from a bib downstream of the check valve and pressure switch and flush the hose onto the ground to remove potential debris.
5. Attach the garden hose to the water wand and insert the wand into the well through the top seal port. (You will have to remove a plug or the well casing vent to do this.)
6. Turn on the garden hose and allow the well pump to cycle, circulating chlorinated water back into the well for approximately 6 hours.
7. Check that there are still adequate free chlorine levels every 2 hours.
8. Turn off the hose, remove the wand and replace the casing vent.
   This procedure will loosen debris in the well. Run the garden hose on the ground until clear to avoid pumping debris into the distribution piping during the next steps. After flushing you may need to add more chlorine to the well to continue.
9. Disinfect the distribution piping by pumping the chlorinated water into the system. Turn on a faucet farthest from the well until significant chlorine can be detected then shut the faucet off. Continue to draw chlorine into the system one or two faucets at a time as described above. Remember hot water taps and toilets too.
10. With no water usage allow the chlorinated water to remain in the pipes for at least twelve hours. More time is better.
11. Flush each faucet one or two at a time until chlorine no longer be detected. Do not turn on so many faucets at a time that the pump cannot keep up and system pressure is lost.

Note: These procedures may need to be modified to be applied to your specific water system.

‌Why did OEHHA update the advisory for eating fish from Lake Mendocino?‌‌‌

OEHHA updated the advisory for Lake Mendocino because additional data became available. This advisory supersedes the previous advisory released in 2009 and is part of an ongoing effort by OEHHA to provide safe-eating advice for fish from different California water bodies. Lake Mendocino is located approximately 5 miles northeast of Ukiah, in Mendocino County.

Why should I eat fish?

The American Heart Association recommends eating at least two servings of fish each week. Low-contaminant fish are an important part of a healthy, well-balanced diet.

Fish are a good source of protein and vitamins, and are a primary dietary source of heart-healthy omega-3 fatty acids. Eating low-contaminant fish while pregnant may be beneficial to the baby’s brain development.

Which contaminant is of concern for people eating fish from Lake Mendocino?

Mercury

• Mercury is a metal that comes from mining, air fallout from burning coal and other fuels, and from natural sources. It is the most commonly found contaminant of concern in fish.
• Too much methylmercury, the form of mercury found in fish, can harm the brain, especially in fetuses, babies, and children. Methylmercury can pass from mothers to their babies during pregnancy.
• Because fetuses, babies, and children are especially sensitive to mercury, OEHHA has one set of advice for how much mercury-containing fish women ages 18–49 years and children should eat, and another set of advice for women 50 years and older and men 18 years and older.

How did OEHHA determine the consumption guidelines for eating fish from Lake Mendocino?

• OEHHA compared contaminant levels in fish caught from Lake Mendocino to levels that are considered safe for human consumption.
• OEHHA’s consumption guidelines balance the health benefits of fish consumption and the risks from the contaminants.

What does OEHHA recommend for people who want to eat fish from Lake Mendocino?

• OEHHA recommends the types and amounts of fish that may be eaten each week as “servings.” A serving is about the size and thickness of your hand for fish fillets. Give children smaller servings. For smaller fish species, several individual fish may be required to yield a serving.
• Women 18–49 years and children 1–17 years
  • Should not eat black bass species or Striped Bassm ay eat:2 total servings per week of Common Carp, or1 total serving per week of Channel Catfish, silverside species, or sunfish species.

• Women 50 years and older and men 18 years and older may eat:
  • 5 total servings per week of Common Carp, or
  • 3 total servings per week of silverside species, or
  • 2 total servings per week of Channel Catfish or sunfish species, or
  • 1 total serving per week of black bass species or Striped Bass.

For additional fish species found in Lake Mendocino and not included in this advisory, OEHHA recommends following the statewide advisory for eating fish from California's lakes and reservoirs without site-specific advice.

How long is the advisory in effect?

This advisory is effective until an update is issued because chemical contaminant levels in fish do not change much over time.

What else can I do to protect my health and the health of my family?

• Eat a variety of fish.
• Eat smaller (younger) fish of legal size.
• Eat only the skinless fillet or meat portion of fish.
• Thoroughly cook the fish and allow the juice to drain away.
• Learn about OEHHA's guidelines for eating sport fish in California:
  • Visit https://oehha.ca.gov/fish/advisories, or call OEHHA at (916) 324-7572 or (510) 622-3170
  • Check the Freshwater or Ocean Sport Fishing Regulations booklets from the California Department of Fish and Wildlife, or visit https://www.wildlife.ca.gov/Regulations.

A harmful algal bloom (HAB) is an overgrowth of algae in a water body that could affect water quality and aquatic life. Some HABs produced by bacteria can create toxins that may also harm people, animals, and the local environment.

How to Identify a Harmful Algal Bloom

Algal blooms can make the water appear green, blue, brown, gold, or red.

Seeing colors, scum, mats, foam, or paint-like streaks in the water or clumps on the shore may indicate a bloom.

However, only professional water testing can confirm if HABs and toxins are present.

States often have monitoring programs for this purpose.

Symptoms of Exposure

• Ear, eye, nose, skin, and throat irritation, and headache

• Paralysis, respiratory illness, and seizures

• Abdominal pain, diarrhea, liver and kidney damage, and vomiting

• Drooling, diarrhea, low energy, not eating, stumbling, tremors, and vomiting

Symptoms vary depending on how the person or animal was exposed and whether the HAB is in salt or fresh water.

If exposed, shower immediately and see a doctor or vet if symptoms occur.

Don't

• Play with scum or mats on the shore
• Let animals drink water, eat algae, or swim
• Swim
• Fish or wade
• Boat or kayak

If a well is found to contain coliform bacteria, it may be possible to eliminate the contamination by disinfecting the well. The goal is to disinfect the well so that coliform bacteria are eliminated. If the well is improperly constructed or located, contamination may not be eliminated or may be eliminated temporarily. In that case, you may need either a new well or an approved disinfection system. Please contact this office to discuss the problem creating the need to disinfect the well.

1. Pump the well to waste for at least 30 minutes. With pump not operating, pour the correct amount of liquid sodium hypochlorite into the well casing. The sodium hypochlorite you use must be ANSI/NSF* Standard 60 certified for potable drinking water. Most wells have a cap or plug that may be removed to pour the liquid into the casing.
   

   Well casing diameter	Amount of 12.5% available hypochlorite solution needed (per 100 feet of well depth)
   4 inches	One cup
   6 inches	Two cups
   8 inches	Three Cups
   12 inches	Eight cups (half gallon)

   Note: These quantities are for 100 feet of well depth. Adjust the quantities to fit the depth of your well. This table is for liquid hypochlorite with 12.5% available chlorine.
2. Do not operate the pump for 30 minutes after adding the hypochlorite. Then surge the well either by turning the pump on and off several times or by connecting a hose to the nearest hose bib and circulating the water into the well casing opening for several minutes.
3. (This step is to disinfect the distribution system if necessary). Start the pump and begin opening taps in the distribution system. Start with the tap closest to the well and let the water flow until a strong odor of chlorine is noted. Then, close the tap and continue procedure until you have detected the chlorinated water at all taps.
4. Allow this water to sit undisturbed in the well and distribution system for 24 hours if possible; or at least overnight. This water should not be used for drinking or bathing.
5. After the 24-hour period or overnight, open all taps (starting with the tap closest to the pump) and allow water to run to waste until no chlorine odor is detected.
6. After the chlorinated water is completely flushed from the well and distribution system, a sample must be collected and analyzed by a certified laboratory. If coliform bacteria are absent, the disinfection has probably been successful. A follow-up sample should be collected from the well after one week. Another follow-up sample should be collected after one month to verify that the water remains free of contamination.

_{*American National Standard Institute (ANSI) or National Sanitation Foundation (NSF}

A quarantine is hereby established on all species of mussels taken for human consumption by recreational sport harvesters from California’s ocean shore. The quarantine area extends from the Oregon border to the Mexican border, including all bays, inlets, and harbors.

This quarantine is to protect and preserve public health under the California Health and Safety Code Section 131056. During the quarantine season, mussels may concentrate naturally occurring toxins that are highly poisonous to humans.

DO NOT EAT MUSSELS HARVESTED IN VIOLATION OF THIS QUARANTINE

State law prohibits the sale or offering for sale for human consumption of any bivalve (two-shelled) shellfish, except by a State-certified commercial shellfish harvester or dealer. Shellfish sold by certified harvesters or dealers are subject to frequent mandatory testing and are not subject to this quarantine.

Mussels may be used or sold for use as bait when displayed and sold in containers labeled in boldfaced type letters at least one-half inch in height as follows:

MUSSELS FOR BAIT ONLY, UNFIT FOR HUMAN FOOD

Clams and Scallops

Persons taking clams or scallops are warned to remove and discard the digestive organs or viscera and any other dark parts. Only the white meat of clams and scallops should be prepared for human consumption. Also, bivalve shellfish should not be taken for food from any area subject to sewage or chemical contamination.

All health officers and their authorized representatives are hereby instructed to enforce the provisions of this quarantine order, which shall be effective May 1 through October 31, 2025. The health officers of the coastal and bay counties are instructed to post copies of this order or other suitable placards in visible places advising the public of this quarantine.

The annual mussel quarantine is for the prevention of paralytic shellfish poisoning (PSP) and domoic acid poisoning and is in effect from May 1 through October 31. This quarantine applies to all species of mussels harvested for human consumption by the public anywhere on the California coast, including all bays and estuaries. Also enclosed is a document containing a summary of the 2024 monitoring results and background information on the PSP toxins and domoic acid.

Press Releases

CDPH will post a notification announcing the annual mussel quarantine. Securing media coverage in all counties is important since PSP outbreaks in the past have involved residents of inland counties as well as those along the coast. Your assistance is requested to ensure that this announcement receives coverage in your area.

Placards

Quarantine placards (or the quarantine notice itself) should be placed in conspicuous locations near popular mussel and clam beds within your jurisdiction to warn the public of the PSP and domoic acid hazard. They also should be provided for display at stores, bait shops, dive shops, public parks and access points, and similar locations along the coast.

Reporting of Shellfish Poisoning Illness

PSP and domoic acid poisoning due are reportable as diseases (Title 17, California Code of Regulations, Sections 2500). Even suspected cases of shellfish poisoning in humans should be reported immediately by telephone to local health departments and by them to the Division of Communicable Disease Control at (510) 620-3434.

Outreach to Groups at High Risk of Shellfish Poisoning

Special efforts to inform high-risk communities of shellfish poisoning hazards should be continued. In addition to recreational harvesters, immigrants from countries with no history of marine toxins, as well as people from areas with no routine toxin monitoring, are particularly at risk of consuming toxic shellfish. This risk is magnified when there is a cultural history of harvesting shellfish for subsistence or ceremonial purposes. Mussel quarantine warning signs in Spanish, Vietnamese, Chinese, Cambodian, Laotian, Ilocano, Hmong, and Tagalog are available from the CDPH Environmental Management Branch (EMB).

Shellfish Toxins Monitoring Program

All coastal county health departments are requested to participate in the shellfish biotoxin monitoring program. If illness and deaths from PSP and domoic acid are to be prevented, it is essential to have periodic sampling data, especially along the open coast, where mussels may commonly be harvested despite quarantine warnings.

Coastal mussel samples also are essential because they provide early warning information needed to keep clam beds open during the quarantine period. If an adequate coastal monitoring program is not maintained, it may be necessary to quarantine all species of sport harvested bivalve mollusks, not just mussels, during the May through October period or longer.

Coastal county health authorities also are invited to participate in a volunteer-based phytoplankton monitoring program. Early detection of toxin-producing phytoplankton can alert CDPH to potentially dangerous toxic blooms before shellfish resources are impacted.

How to Sample and Submit Shellfish Specimens for Testing

Each coastal county health department is requested to submit shellfish samples (mussels from the outer coast are preferred) from one to two representative sites, approximately once to twice per month year-round, as weather and tidal conditions permit. Please note that at least 200 grams of shellfish meat (approximately one cup) are requested. Shipping containers and detailed instructions can be obtained by contacting the CDPH EMB Biotoxin Monitoring Program.

You will be notified promptly of laboratory test results if any sample equals or exceeds the federally established "alert" level of 80 micrograms of PSP toxins per 100 grams of shellfish meat or 20 parts per million (ppm) for domoic acid. In addition, all coastal county health departments and other sampling program participants receive monthly and annual reports summarizing shellfish testing results for the entire coast of California.

Shellfish Information

CDPH maintains an interactive map of the recreational bivalve shellfish health advisories and recent biotoxin results that can be found online.

The CDPH Biotoxin Information Line, with recorded updates on shellfish biotoxins and quarantines, is a toll-free telephone number at 1-800-553-4133.

CDPH has developed a “Frequently Asked Questions” (FAQ) for the annual mussel quarantine that can be found online. 

Additional information about the CDPH Biotoxin Monitoring Program can be found online. 

If you have questions about the annual mussel quarantine or the CDPH Biotoxin Monitoring program, please contact Vanessa Zubkousky-White, coordinator of the EMB Marine Biotoxin Monitoring Program at Vanessa.Zubkousky@cdph.ca.gov or (510) 412-4635; questions about human shellfish poisoning cases may be directed to the Infectious Diseases Branch at (510) 620-3434.

Vanessa Zubkousky-White
Senior Environmental Scientist

Enclosures

This information is provided for the preparation of press releases, answering inquiries from the public, and other purposes related to shellfish poisoning and the annual mussel quarantine. Questions and requests for additional information about the quarantine may be directed to the California Department of Public Health (CDPH), Environmental Management Branch [Vanessa Zubkousky-White, Marine Biotoxin Monitoring Program, at

510-412-4635]. Questions about human shellfish poisoning cases may be directed to the Infectious Diseases Branch at 510-620-3434.

Introduction

The annual quarantine on sport-harvested mussels is normally in effect from May 1 through October 31. Occasionally the annual quarantine will begin sooner than May 1 due to significant increases in toxin levels earlier in the year. Similarly, a biotoxin event may persist beyond the end of October, resulting in an extension of the annual quarantine for one or more counties. The annual mussel quarantine applies to the entire coastline of California, including all bays, inlets, and harbors. The main purpose of the quarantine is to protect the public from the toxins that cause paralytic shellfish poisoning (PSP) and domoic acid poisoning, also known as amnesic shellfish poisoning. Both of these syndromes are associated with consumption of bivalve (two-shelled) mollusks, such as mussels, clams, oysters, and scallops, which feed by filtering tiny particles from the water. Domoic acid has also been found at levels of concern in the viscera and flesh of crustaceans like crab and small finfish like anchovies and sardines.

The mussel quarantine restrictions and recommendations apply only to shellfish collected by sport harvesters. Mussels and other bivalve mollusks harvested by state-certified shellfish growers and sold commercially in markets and restaurants should pose no risk of PSP and domoic acid poisoning to consumers as they are closely monitored and

tested. Since the PSP outbreak in 1980 included illnesses from consumption of commercially harvested oysters, commercial shellfish producers have been required to submit specimens weekly from all commercial harvest areas for PSP assay by CDPH. Bivalve mollusks imported into California are similarly monitored for biotoxins by the producer states.

Shellfish toxin levels do not rise and fall in predictable cycles and can increase rapidly. Prevention of human illnesses requires strict enforcement of the annual quarantine, combined with year-round surveillance, public education, occasional special health advisories and commercial closures as needed.

Reporting of Suspected PSP and Domoic Acid Poisoning in Humans

PSP and domoic acid poisoning are immediately reportable to the local health authority (Title 17, California Code of Regulations, Sections 2500). Even suspected cases should be reported immediately by telephone to the local health department and to the nearest poison control center. Local health departments should interview patients regarding shellfish exposure and report these cases promptly to the Infectious Diseases Branch at 510-620-3434.

Paralytic Shellfish Poisoning (PSP)

1. The Ecology and History of PSP in California

   The source of the PSP toxins in bivalve mollusks is a dinoflagellate known as Alexandrium catenella. Unfortunately, unlike some parts of the world where visible blooms of Alexandrium occur, it is highly unusual to experience a ‘red tide’ of this dinoflagellate along the California coast. Because the PSP toxins produced by Alexandrium are so potent, it takes very few cells in the water to create a public health risk from shellfish consumption. Therefore, visual cues of ocean color are not reliable indicators of safe or unsafe conditions for shellfish harvesting and consumption. Shellfish can develop extremely hazardous levels of toxin within a few days without any visible warning. Conversely, the majority of red tides observed along the California coast are associated with nontoxic species of dinoflagellates. Elevated levels of the PSP toxins have historically been detected in mussels, oysters, scallop viscera, clams, abalone jingles, and gooseneck barnacles. Red abalone, crab, and shrimp have not been the source of any cases of PSP in California, although the latter two crustaceans could potentially accumulate PSP toxins in the internal organs. In California, PSP toxins are detected in shellfish most commonly during the warm spring, summer, and early fall months, although episodes of high toxicity in shellfish have occurred during the winter months also.

2. PSP in Humans

   Symptoms of PSP poisoning can occur within a few minutes to a few hours of consumption of contaminated seafood. Symptoms may begin with tingling and numbness of the lips, tongue, and fingertips, followed by slurred speech, difficulty in swallowing, disturbed balance, and lack of muscular coordination. Respiratory failure and death may occur without proper medical care. Treatment is supportive, including mechanical ventilation for severe cases; there is no known antidote to the toxin. Symptoms tend to resolve completely within a few days. Diagnosis is based on clinical presentation, compatible food history, and detection of elevated saxitoxin from the suspected seafood. Persons experiencing PSP symptoms should immediately seek medical treatment.

   PSP was made a reportable disease in 1927. There is some limited information about cases prior to 1927 although there could be underreporting during this time. Since 1903, 582 illnesses due to PSP have been reported in California; 39 patients have died. Over 99 percent of these illnesses have occurred during the months of May through October. The last major PSP outbreak in California occurred in July 1980 with 98 illnesses and 2 deaths. In August 1991, 11 non-fatal illnesses due to PSP, including 3 hospitalizations, were reported in persons who had eaten mussels they had collected in northern Sonoma County. In March 2018, 1 non-fatal illness due to PSP resulting in hospitalization occurred in a patient who ate mussels collected in northern Marin County.

3. PSP Toxins in 2024

   Alexandrium was observed at sites along all coastal counties during 2024, except Monterey where there were limited phytoplankton samples. This dinoflagellate was observed during all months in 2024, and it occurred at multiple sites along the California coast sporadically throughout the year. The highest percent composition was observed in September at Morro Bay in San Luis Obispo County.

   Measurable concentrations of PSP toxins were found in 147 shellfish samples from the following coastal counties: Del Norte, Humboldt, Mendocino, Sonoma, Marin, San Francisco, San Mateo, Santa Cruz, Monterey, San Luis Obispo, Los Angeles, Orange, and San Diego. Detection of measurable PSP toxins occurred during the months of May through December. Concentrations of PSP toxins greater than or equal to the alert level (80 μg/100 g of tissue) were detected in samples from Del Norte, Humboldt, Sonoma, Marin, Santa Cruz, and Monterey counties. The highest concentration detected was in a mussel sample was 840 μg/100 g PSP toxins collected July 9 at Hunter Rock in Del Norte County.

4. PSP Toxins in Early 2025

   Measurable concentrations of PSP toxins were found in shellfish samples from the following coastal counties: Santa Barbara, Ventura, Los Angeles, Orange, and San Diego. Detection of measurable PSP toxins occurred during the months of January through April. Concentrations of PSP toxins greater than or equal to the alert level (80 μg/100 g of tissue) were detected in samples from Santa Barbara and San Diego counties. The highest concentration detected was in a mussel sample was 1,518 μg/100 g PSP toxins collected April 14 at an aquaculture site offshore of Santa Barbara.

Domoic Acid

1. The Ecology and History of Domoic Acid in California

   In 1987, domoic acid was first recognized as a cause of poisoning in humans when approximately 150 persons in Canada became ill and four died after consuming toxic mussels from Prince Edward Island on the Canadian Atlantic coast. The source of the domoic acid in this outbreak was a diatom known as Pseudo-nitzschia pungens forma multiseries. This single-celled marine algae, like dinoflagellates, is a natural food source for filter-feeding animals.

   The first documented occurrence of domoic acid on the Pacific Coast of the United States was in September and October 1991 in the vicinity of Santa Cruz, on Monterey Bay. In this episode it was found to be the cause of death of several hundred brown pelicans and Brandt's cormorants. The birds were exposed to domoic acid by feeding on anchovies, which had fed on a bloom of the diatom Pseudo-nitzschia australis. Prior to the 1991 event, there is evidence that Pseudo-nitzschia was abundant in Monterey Bay in 1961 during a sooty shearwater die off, inspiring Hitchcock’s film The Birds.

   Subsequent sampling revealed elevated concentrations of domoic acid in mussels at several locations around Monterey Bay, and elevated levels also were found in razor clams sampled in Humboldt and Del Norte Counties. The high levels of domoic acid in Monterey Bay coincided with a bloom of the diatom Pseudo-nitzschia australis, and the toxin also was found in plankton samples containing mostly this diatom species. Low concentrations of domoic acid have subsequently been found in mussels from almost every coastal county in California.

   Similar domoic acid events occurred in May 1998, the summer of 2000, and the spring of 2015 along the San Luis Obispo County coast and in Monterey Bay. These events involved illness or death in large numbers of California sea lions and, as in 1991, anchovies and sardines again appeared to be responsible for providing a pathway for toxin transport from the diatoms to the marine mammals. Volunteer phytoplankton observers were instrumental in CDPH’s ability to detect and track these blooms. Intensive sampling of a variety of seafood species determined that high concentrations of domoic acid could be found in a number of bivalve shellfish, like mussels and oysters, as well as in the digestive gland of crabs, spiny lobsters, sardines and anchovies. Persistent elevated levels of domoic acid have been detected in razor clam meat from Humboldt and Del Norte counties since 2015. Domoic acid also has been found in Oregon and Washington in razor clams, mussels, and crabs.

   The seasonal pattern of occurrence of Pseudo-nitzschia and domoic acid has changed significantly since monitoring began in 1991. The initial event in Monterey Bay occurred in the fall and phytoplankton monitoring in the years immediately following this event confirmed this seasonal pattern of increase in Pseudo-nitzschia. There was very little domoic acid toxicity detected through the remainder of the 90’s, although there was a large-scale marine mammal mortality event due to domoic acid in 1998 as noted above. During 2000 there was a noticeable increase in domoic acid activity in Monterey Bay and along the San Luis Obispo County coast during the summer months, extending into November at some locations. In 2002 there was an early spring increase in Pseudo-nitzschia and domoic acid concentrations. This event began in Monterey Bay in February and appeared to ‘move’ down the coast between San Luis Obispo and Los Angeles Counties through June. This spring bloom pattern persisted through most of the remainder of the decade, although a smaller fall event occurred in 2009 and a winter event occurred in Santa Barbara County in 2011. In 2015, domoic acid was detected in shellfish from Del Norte County to Los Angeles County when a large bloom of Pseudo-nitzschia persisted off the west coast of North America from California to Alaska. In 2017 domoic acid was again detected over a large range of the coast with elevated levels in

   mussels from Del Norte, Monterey, Santa Barbara, Ventura, and Los Angeles counties. The changing seasonality and distribution of Pseudo-nitzschia, and subsequently of domoic acid concentrations in seafood, reinforces the need for a rigorous monitoring program throughout the year to ensure public health protection.

   Extensive phytoplankton sampling is being conducted to investigate the spatial and temporal distribution of the diatoms associated with domoic acid production. Extensive blooms of the diatoms that produce domoic acid have been detected and followed along most coastal counties since this program began.

   These environmental observations provide an early warning to potentially toxic blooms, allowing CDPH to respond quickly with intensified sampling and toxin analysis in the affected area.

2. Domoic Acid Poisoning (Amnesic Shellfish Poisoning) in Humans

   Within 24 hours of eating contaminated shellfish, patients develop gastrointestinal symptoms such as diarrhea, vomiting, and abdominal pain, followed by headache, memory loss, and disorientation. In severe cases, domoic acid poisoning can cause cardiovascular instability, seizures, coma, and death. Survivors may experience anterograde short-term memory loss (i.e., inability to recall the recent past). Diagnosis is based on clinical presentation, compatible food history, and detection of domoic acid from the suspected seafood. As with PSP, medical therapy consists of supportive care; there is no known antidote to the toxin, and persons experiencing symptoms should receive immediate medical attention.

   Domoic acid poisoning in humans associated with the consumption of shellfish harvested in California has not been reported.

3. Domoic Acid in 2024

   Pseudo-nitzschia was observed at sites along all coastal counties during 2024. This diatom was observed during every month in 2024. Elevated percent composition was observed during May in Santa Barbara County, August in Humboldt and San Luis Obispo counties, and September in San Luis Obispo and Santa Barbara counties.

   Measurable concentrations of domoic acid were found in 25 shellfish samples, not including razor clam samples. These were from Del Norte, Humboldt, and Santa Barbara counties collected between July and October. Concentrations of domoic acid greater than or equal to the alert level (20 µg/g of shellfish meat, or 20 parts per million [ppm]) were detected in samples from Humboldt and Santa Barbara counties. The highest concentration detected was 45 ppm domoic acid in a mussel sample collected September 23 at an aquaculture site offshore of Santa Barbara.

   Razor clam samples from Del Norte and Humboldt counties had measurable concentrations of domoic acid throughout 2024. Concentrations of domoic acid above the alert level (20 µg/g of shellfish meat, or 20 parts per million [ppm]) reached 230 ppm in razor clams from Humboldt County in October.

   More information on crab monitoring data from 2024 and associated health advisories is available at the following link: https://www.cdph.ca.gov/Programs/CEH/DFDCS/Pages/FDBPrograms/FoodSafetyProgr am/DomoicAcid.aspx

4. Domoic Acid in Early 2025

   Measurable concentrations of domoic acid were found in shellfish samples, not including razor clam samples, from Santa Cruz, San Luis Obispo, Santa Barbara, Los Angeles, and San Diego counties collected between January and April 2025.

   Concentrations of domoic acid greater than or equal to the alert level (20 µg/g of shellfish meat, or 20 parts per million [ppm]) were detected in samples from Santa Barbara, Los Angeles, and San Diego counties. The highest concentration detected was 27 ppm domoic acid in a mussel sample collected April 1 at La Jolla Pier in San Diego County.

   Razor clam samples from Del Norte and Humboldt counties had concentrations of domoic acid above the alert level (20 µg/g of shellfish meat, or 20 parts per million [ppm]) in January (both) and April (Humboldt). The highest concentration detected was 280 ppm in razor clams from Humboldt County in January.

Special Risks from Various Kinds of Seafood

The greatest hazard for PSP and domoic acid poisoning is from the consumption of mussels (see also discussion below on razor clams) because: (1) they concentrate the toxins more quickly and to higher levels than do other shellfish, (2) they generally occur along the open coast where they are directly affected by oceanic blooms, and (3) they are eaten whole without removal of digestive organs. The digestive organs of crustaceans such as lobster and crab, as well as of small finfish like sardine and anchovy, can also contain dangerous levels of domoic acid, as can the flesh. Other contaminants can also be concentrated in the viscera, so the public is advised to avoid consuming the internal organs of any seafood species.

The consumer cannot distinguish toxic mussels from harmless ones. Moreover, cooking cannot be relied upon to destroy the toxins because they are relatively heat stable. The safest guideline for consumers is: Do not eat mussels taken by recreational

sport-harvesters from California coastal waters during the annual quarantine months of May through October. During other months, visit the website for a map of the current recreational bivalve shellfish health advisories (https://experience.arcgis.com/experience/394836318cfe4f7494e1c09097a43559/) or call the CDPH "Biotoxin Information Line" at 1-800-553-4133 for an up-to-date, recorded message of any special health advisories.

While clams can develop hazardous levels of PSP toxin, they are placed under quarantine only in localized areas when tests reveal the presence of elevated toxin levels in mussels in the vicinity of clam beds or in clams themselves. In clams, the toxin is concentrated primarily in the digestive organs (dark meat), hence, these portions from all types of clams should always be discarded; only the white meat should be eaten.

A special hazard is presented by the Washington or butter clam (Saxidomus spp.). They may concentrate the PSP toxins in the neck or siphon (the tube-like part of the clam that sticks out between the shells). It has been found that PSP toxin in the necks of Washington clams may persist for a year or more after a PSP toxin event.

Northern razor clams (Siliqua patula) have been found to present a special risk for domoic acid poisoning because they concentrate this toxin in the white meat of the foot and siphon, parts that normally are preferred for human consumption. Razor clams are able to retain this toxin for extended periods, just as the Washington clam retains the PSP toxins.

Scallops from California waters may also become toxic. This is true for both the adductor muscles (the "scallop" or white meat that is ordinarily eaten) and the digestive organs (the darkish soft tissue of a scallop left after the white adductor muscle has been removed). In August 1980, a man died of PSP after eating only the digestive organs of a single rock scallop (Hinnites giganteus) taken by a sport-diver on the Sonoma County

coast. Subsequent investigations revealed that a lower, but still hazardous, concentration of the toxin also may occur in scallop adductor muscles during a PSP episode. The digestive organs of scallops should never be eaten as they may remain toxic

year-round. It is unknown how long PSP toxins may persist in the white meat of scallop adductor muscles.

Groups at Special Risk of Shellfish Poisoning

In addition to recreational harvesters, immigrants from countries with no history of marine toxins, as well as people from areas with no routine toxin monitoring, are particularly at risk of consuming toxic shellfish. This risk is magnified when there is a cultural history of harvesting shellfish for subsistence or ceremonial purposes. CDPH has a number of alternative language quarantine signs available to county health departments and community-based outreach organizations. https://cdphdata.maps.arcgis.com/sharing/rest/content/items/28d01a8b6dc44e59abb719c 91c6c02d5/data

1. Infectious Disease Hazards

   Bivalve shellfish should never be taken from waters contaminated by sewage or other pollutants because they also can concentrate disease-producing bacteria and enteroviruses, such as Hepatitis A virus.

   
   

2. Public Information Available

CDPH has developed a “Frequently Asked Questions” (FAQ) for the annual mussel quarantine that can be found online.

EMB maintains a toll-free "Biotoxin Information Line" with recorded updates on shellfish biotoxins and quarantines at 1-800-553-4133.

EMB also maintains an interactive map of the recreational bivalve shellfish health advisories and links to recent biotoxin data PDFs.

An information leaflet entitled "Natural Marine Toxins" is produced by CDPH and the University of California Cooperative Extension.

Press releases are prepared by CDPH to announce the annual mussel quarantine and any health advisories issued. These can be found online.

Monthly reports issued by CDPH are available that include summary information and maps of PSP toxicity and toxigenic phytoplankton distributions along the coast. The monthly and annual reports can be found online or by contacting redtide@cdph.ca.gov.