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While recreational shellfish harvesting is a year-round activity, it is especially popular in the summer when warmer weather and mid-day low tides make it easier. However, warmer temperatures can also create conditions for marine (saltwater) biotoxins. Marine biotoxins are poisons that accumulate in shellfish, under the right conditions (warm temperatures, sunlight, and nutrient-rich waters). Cooking the shellfish doesn’t get rid of the toxins, which means eating shellfish with biotoxins can make you really sick, or even kill you.
To reduce your risk, always check the Washington State Department of Health’s (DOH) Shellfish Safety Map (website in English only) before collecting shellfish. The shellfish safety map is updated daily and is the best source of information for closures. It shows which areas are safe for recreational shellfish harvesting, and which are closed due to dangerous toxins or pollution.
When you arrive at a shellfish harvesting site, also look for shellfish closure signs. They are bright red and look like this picture.
Signs like these will be posted at shellfish harvesting sites when the site is closed.
Testing shellfish for toxins
How does DOH know whether shellfish are safe for harvesting or not? The answer is regular, frequent shellfish testing, which local health agencies (like us!) conduct in partnership with DOH. My Environmental Health colleague Leonard is out on King County beaches and marinas all summer long, from May to October. He collects blue mussels and butter clams and delivers them to DOH’s laboratory. DOH then tests the shellfish to see if any areas should be closed. As they say, it takes a village!
Recently, I tagged along with him to see what it’s like. Our first stop was at a marina in South King County. Down a dock, Leonard pulled up a box of mussels that was encrusted with barnacles. He partially filled a bucket with mussels from the box (releasing a couple of opportunistic eels that had swum in looking for a snack), before washing the mussels and cleaning off the box. This is an important step – we want water to be able to flow in and out of the box, so the mussels continue to ingest it. Then, when DOH tests the mussels, they’ll get a good idea of what the water is like. All in all, it’s a quick stop!
The next stop, further south, is a bit more involved. This time, we’re here to dig for clams – butter clams, specifically. We don’t need to walk far – after 20 years, Leonard has a good sense of where to look. This is where I have to admit that despite growing up in the area, this was my first time digging clams! Thankfully, Leonard is a great teacher. He showed me what to look for in the sand, and where to start digging. He also showed me how to identify butter clams, which have horizontal lines running across the shell. They’re bigger than the other species you’ll see, like littlenecks (which have vertical lines from the base to opening). We look for butter clams specifically because they retain toxins longer than other species. This makes them better for testing.
After a quick stop for lunch, we visited two more locations – another one to dig clams, and another one to collect mussels. After that, the day ended with a trip up to the DOH Public Health Lab in Shoreline. There, they’ll analyze the shellfish for biotoxins. The results help them decide whether to close areas to recreational harvesting right away, or forecast when closures might be required.
Harvest safely and learn more
If you’re heading out to dig shellfish, always check the map first to what areas are open and safe (website is in English only). When you’re on-site, look for emergency closure signs like the one pictured at the beginning of this blog. Shellfish harvesting can be a great year-round activity, but as always, it’s important to know before you go.
You should also check the Washington Department of Fish and Wildlife’s harvesting shellfish webpage (website is in English only) to learn about harvesting season, sizes and limits. You can learn more about biotoxins on the state’s Marine Biotoxin’s webpage (webpage is in English only).
Originally published 6/11/24