PORT TOWNSEND — The state has closed Fort Flagler State Park and Mystery Bay State Park to shellfish harvesting because biotoxins that cause paralytic shellfish poisoning have been detected at lethal concentrations.

Paralytic shellfish poisoning (PSP) concentrations rose to more than 1,700 micrograms per 100 grams of shellfish in samples taken this week, according to the state Department of Health. The closure level is 80 micrograms.

Such high amounts of toxins are potentially lethal, the state says; PSP in such high concentrations is likely to be fatal. PSP is a nerve toxin deadly to both humans and animals.

“It was unusual this time how it went from nontoxic to very toxic in a short space of time,” said Michael Dawson, water quality manager for Jefferson County Public Health.

“I’m not sure why it developed so rapidly.”

The harvesting season at Mystery Bay is closed at this time anyway, Dawson said.

But Fort Flagler is a popular shellfishing beach.

“Normally it’s open through the end of December,” Dawson said. “Hopefully there will be some clamming opportunities later in the year.”

The closure extends to clams, oysters, mussels, scallops and other species of molluscan shellfish.

It does not include crabs at Fort Flagler, Dawson pointed out, adding that the crabbing season ends Monday.

“For this weekend coming up, crabbing is still open at Fort Flagler,” Dawson said.

Crab meat is not known to contain the biotoxin but the guts can contain unsafe levels, experts say.

To be safe, they advise cleaning crabs thoroughly and discarding the guts (butter).

Shellfish harvested commercially are tested for toxin prior to distribution and should be safe to eat, the state said.

Danger signs have been posted at high-use beaches, warning people not to consume shellfish from the area.

Paralytic Shellfish Poison (PSP) is a naturally occurring marine biotoxin that is produced by some species of microscopic algae. Shellfish eat these algae and can retain the toxin.

Symptoms of PSP can appear within minutes or hours after consumption and usually begin with tingling lips and tongue, moving to the hands and feet, followed by difficulty breathing and possibly, death. Anyone experiencing symptoms should contact a health care provider immediately and, for extreme reactions, call 9-1-1.

Dawson said algae blooms are common in the area in late summer.

“We had a pretty good year in Jefferson County for biotoxins in spite of the warm weather. It held off until now,” Dawson said.

He said it is difficult to predict how long the toxins will remain at high levels.

Once toxins recede and allow most species to be harvested, some species — butter clams and varnish clams — will continue to be contaminated for months.

Elsewhere, Sequim Bay was closed to recreational harvesting last week because of a high level of toxin that causes diarrhetic shellfish poisoning (DSP).

This is a less serious illness than that caused by PSP. DSP can cause diarrhea, nausea, vomiting, abdominal cramps and chills.

Beaches on the Strait of Juan de Fuca remain open to harvesting of all species.

Discovery Bay and Port Ludlow including Mats Mats Bay are closed for the harvest of butter clams and varnish clams only.

Ocean beaches are under an extended seasonal closure.

Toxins cannot be detected by sight or smell. Neither cooking nor freezing destroys biotoxins.

Recreational shellfish harvesters can get the latest information before they leave for the beach by visiting www.doh.wa.gov or calling 800-562-5632.

The emergency regulation hotline is 866-880-5431.

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Executive Editor Leah Leach can be reached at 360-417-3530 or at lleach@peninsuladailynews.com.