To be fair, part of this is natural and seasonal. Most of natural marine biotoxins are seasonal and the department of health tests regularly. I don't know to what extent the biotoxins are affected by pollution (e.g., fertilizer runoff), but they are a natural occurrence.

Separately, they also have permanently closed the tidelands near Seattle due to pollution. Crabbing is still open each summer, but bivalves are closed.

I was just out on Whidbey Island a couple of weeks ago where I found and ate raw oysters on the beach, then dug clams and brought them home for dinner. The pollution does concern me, but I do trust the government testing. Its also worth noting that the oysters & other bivalves you eat in restaurants come from the same waters.