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The Washington State Department of Health has closed Quartermaster Harbor beaches to recreational shellfish harvest — including  clams, oysters, mussels, oysters, geoduck and scallops — after diarrhetic shellfish poison (DSP) was detected at unsafe levels in area shellfish on Vashon-Maury Island.

Public Health – Seattle & King County posted advisory signs at beaches warning people to not collect shellfish, according to a news release sent Thursday afternoon. Commercial beaches are sampled separately and commercial products should be safe to eat. Although DSP has been a problem in European countries, it’s an emerging health threat for Washington.

DSP comes from naturally occurring algae that produces the toxin. It can’t be destroyed by cooking or freezing. A person cannot determine if DSP toxin is present by visual inspection of the water or shellfish.  DSP can only be detected by laboratory testing.

DSP poisoning symptoms include nausea, vomiting, abdominal pain and diarrhea, with diarrhea being the most commonly reported symptom. Symptoms may appear within minutes of eating contaminated shellfish or may take several hours to develop.

Recreational shellfish harvesting can be closed due to rising levels of DSP at any time. The department advises harvesters to call its Biotoxin Hotline at 1-800-562-5632 or visit the Biotoxin Website before harvesting shellfish anywhere in Puget Sound.