Health officials issued the closure after finding elevated levels of Diarrhetic Shellfish Poison or DSP, a naturally-occurring biotoxin, in areas ranging from Bellingham to Seattle. The San Juan Islands are not included - the islands are only closed for harvesting of butter and varnish clams.
Cross-hatching shows the areas closed to to recreational shellfish harvesting. The diagonal lines in the San Juans indicate the area closed to butter and varnish clams. View a larger map on the Department of Health website.
Jerry Borchert studies marine biotoxins for the Washington State Department of Health.
"These four areas that closed down here recently, they were scattered throughout Puget Sound, which makes it kind of interesting that we see such a large coverage of different areas closing down," says Borchert.
All species of shellfish are affected by the toxin, including clams, oysters, mussels, and scallops. Borchert says freezing or cooking does not eliminate DSP.
Commercial shellfish, which are tested separately, are still considered safe to eat.
DSP has been rampant in Europe for many years. The first known case of illness in the U.S. occurred in 2011.
Borchert says the health department has been monitoring DSP since then, and he has seen it come and go frequently in Washington.
While the biotoxin is not lethal, it can make a person very ill.
Borchert says symptoms can show up within half an hour.
"Basically the symptoms are vomiting and diarrhea, or could just be some intense cramping. And typically they last a few hours, but they could last as long as a day."
Borchert says anyone who believes they have ingested the toxin should call their local health provider. A map of beaches closed to shellfish harvesting is on the Washington State Department of Health's website, and will be updated after the next round of tests.