Whatcom County beaches south of Point Whitehorn are again closed to recreational shellfish harvesting because of unsafe levels of paralytic shellfish poison, health officials said Wednesday, Oct. 19.

Beaches north of Point Whitehorn, near Birch Bay, were closed only to the harvest of varnish clams.

Paralytic shellfish poison biotoxins can cause death. They are found in naturally occurring algae. Molluscan shellfish have difficulty filtering out the biotoxin, leading to an unsafe buildup in the flesh of clams, mussels, scallops and other shellfish.

Shellfish sold in stores are tested before they are shipped to retailers and are safe to eat, according to the county Health Department.

Crab meat isn't affected, but "crab butter" and crab entrails can harbor the biotoxin, which is not destroyed by cooking or freezing.

County beaches have been closed to shellfish harvesting several times in the past year, and most recently reopened to the harvesting of most shellfish about a month ago.