Islanders cruising along Quartermaster Drive on Monday were surprised to see bright orange water lapping up along the edge of Quartermaster Harbor at Portage.

Frank Cox, a spokesman for the state Department of Health’s shellfish program, said the bright red or orange water that many refer to as “red tide” and believe to be toxic is actually caused by a non-toxic noctiluca algea bloom.

Conversely, Cox said, the harmful blooms that cause paralytic shellfish poisoning — and which lead to clamming bans at Quartermaster and other Vashon beaches — often cannot be seen.

Quartermaster Harbor is currently open to the harvesting of all clams except butter clams, and Cox said it will likely open for butter clams soon.

“Mussel samples since the first of the year have all been no toxins detected,” he said.

However, Cox added that Quartermaster has historically experienced periods of very strong paralytic shellfish poisoning blooms. The toxic algae blooms close the harbor to clamming at least once a year, he said, and as recently as 2006 shellfish from the harbor were found to have lethal levels of biotoxins, which cannot be killed with cooking or freezing.

“Some years it goes very, very toxic there,” he said.

Even when the harbor is clear of toxic algae as it is now, clam diggers may have more luck on Vashon’s outer beaches. Over half of the harbor’s shoreline is permanently closed to harvesting due to pollution.

Know before you dig

Updated information on beach closures due to paralytic shellfish poisoning blooms can be found at www.doh.wa.gov/ehp/sf/recshell.htm or by calling the 24-hour Shellfish Safety Hotline at 1-800-562-5632.