The Washington State Department of Health has closed Oak Bay for recreational shellfish harvest for butter and varnish clams, health officials announced Monday.

The closure came after a recent clam sample in Oak Bay was found to contain elevated levels of the marine biotoxin that causes Paralytic Shellfish Poisoning (PSP).

Danger signs have been posted at public access points warning people not to consume butter or varnish clams from the area.

Officials said other shellfish species are not affected.

Water Quality Manager Michael Dawson of Jefferson County Public Health said the samples were collected Thursday, Aug. 25.

Signs were posted Friday, Aug. 26.

Health officials warned that PSP can be fatal.

Illness is caused by eating shellfish contaminated with toxins from the naturally occurring marine plankton Alexandrium, and biotoxins are not destroyed by cooking.

Symptoms of PSP can appear within minutes or hours and usually begin with tingling lips and tongue, moving to the hands and feet, followed by difficulty breathing, and paralysis.

People who experience any such symptoms after consuming shellfish should contact a health care provider immediately, or call 911 in case of an extreme reaction.