Last month’s routine testing of wild shellfish revealed high levels of a deadly toxin, prompting a warning for harvesters to avoid eating their catch until it has been professionally cleared.

The Earth Branch of the WCA issued the alert after discovering paralytic shellfish poisoning (PSP) in samples taken April 28 near Shoemaker Bay. They sampled butter clams, cockles and blue mussels.

PSP is a naturally occurring biotoxin produced by certain types of microscopic algae. When shellfish eat these algae, the toxin builds up in their tissue.

WCA Earth Branch Coordinator Kim Wickman said samples are collected every two to three weeks and results typically take about seven days to return.

“What we’re advising people is to go ahead and process your shellfish and then freeze it. Bring us a sample of six different clams — larger ones — and we can send it off to get tested,” Wickman said. “And if you harvested wild shellfish from two different locations, you need to keep them separate from each other and send samples from both.”

The toxin affects the human nervous system and can paralyze muscles. In high doses, it can cause severe illness or death. Symptoms of PSP can appear within minutes and include numbness or tingling in the lips and fingertips, a “floating” sensation and nausea.

Health officials warn that cooking or freezing shellfish does not destroy the toxin because it is heat-stable and remains dangerous even after boiling.

While most shellfish clear the toxin relatively quickly, some species are more stubborn.

“Most clams will filter out the toxin within one week, so it doesn’t last long,” Wickman said. “But butter clams can actually keep the toxin for as long as four years.”

Butter clams are identified by their heavy, thick shells and deep rings. Other species at risk include mussels, oysters, geoduck, and scallops. Crab can also become toxic because they feed on these shellfish.

Wickman noted that the warning only applies to wild shellfish.

“Canoe Lagoon products are fine,” she said of the commercial supplier in town. “They have to do lots of testing and their products are tested. There isn’t any concern there.”

A new sample of blue mussels was recently submitted for testing to determine if the danger is passing.

“Blue mussels are an indicator species. If that test comes back clear, we’ll get a full sample of blue mussels, butter clams and cockles,” Wickman said. “If that full sample comes back clear then we can remove the warning.”

Harvesters can bring samples of six to eight midsize clams to the WCA office at 1002 Zimovia Highway. For more information, the public can contact Wickman or Lexie Hayes at 907-874-4304.