Paralytic Shellfish Poisoning

Paralytic Shellfish Poisoning, or in layman’s terms “Red Tide,” is a naturally occurring biotoxin that is produced by some species of microscopic algae.  Because shellfish are filter feeders, they pump water through their bodies straining out and eating algae and other food particles. When they eat biotoxin-producing algae, the toxin can accumulate in their tissue causing illness in humans who consume them.  

The Washington State Department of Health has a Biotoxin Program that performs year-round monitoring of PSP and Amnesic Shellfish Poison (ASP, or domoic acid) in molluscan shellfish. Puget Sound Restoration Fund assists the Washington State Department of Health in the collection of shellfish samples around Puget Sound. Managing volunteers from 20 distinct sampling sites, PSRF ensures samples from each site arrive in Shoreline at the WA Department of Health State Lab in a timely fashion. Samples are processed quickly and results are immediately used to update harvest openings and closures.

If you intend to harvest shellfish from any beach - public or private- you should check with the WA DOH hotline 1-800-562-5632. You can also look on their website for beach closure information.  Both the hotline and the website are updated as soon as results are available.

*Shellfish harvested commercially and sold to the public come from licensed, certified growers.  Commercial harvest operations must meet stringent state and federal health standards, and the shellfish they harvest are regularly tested for biotoxins.

More about PSP

PSP in Washington is caused by phytoplankton known as Alexandrium catanella. This phytoplankton often blooms alongside other algae and plankton. Therefore, when you see the water is red, you know there is a bloom of some sort going on, but not necessarily Alexandrium. Conversely, if the water is clear, it does not mean that shellfish are safe to eat. After a bloom passes it takes several weeks for most shellfish to excrete all remains of the biotoxin. The butter clam in particular takes months to reach a safe consumption status - lucky for them, but no good for someone hoping to make chowder.

Back in the old days seafaring folks would carry a cat on board their vessel so they could feed them a sample of their shellfish catch. If the cat survived, the shellfish was on the table for dinner. Scientists at Wood's Hole Oceanographic Institute have teamed up with the Department of Health. They are hoping to learn more about the Alexandrium species. Specifically they are looking at how levels of A. catanella in the water column are associated with levels of toxicity in shellfish. Perhaps one day not too far away, scientists will be able to use water samples as an early detection method for PSP blooms.

In the meantime I recommend carrying your neighbor's cat to the beach with you - or at least your cell phone.

More information regarding biotoxins

If you have an interest in volunteering to sample shellfish at one of our sites, please contact us at or 206.780-6947