Oregon State Clam Digging: "shellfish:
Paralytic Shellfish Poisoning - also known as “red tide” - happens when shellfish take in a lot of algae that has a toxin that is bad for humans. PSP is often linked to warm conditions and huge algae blooms. PSP is not usually a concern in cold Alaskan and Pacific Northwest waters, but scientists still test razor clams for the toxin.
Domoic Acid is the other worry before the beaches open for a razor clam dig. Domoic Acid is a natural ocean poison that clams, which feed on material in the water, absorb in their body tissues - especially fat.
High levels of Domoic Acid - starting at about 20 parts per million - can make people sick."