Eat scallops - forget everything else.

Here is a link to a Telegraph article about a Michelin-starred chef in Spain who allegedly served shellfish from a water source known to be contaminated with diatoms (small protists) that produces domoic acid.

Spanish Michelin star chef arrested over toxic shellfish

Domoic acid is considered a marine toxin.  It can cause an illness called Amnesic Shellfish poisoning.  I'll let you read about it and its effects here.  Yes, it's a Wikipedia article.  But it is the clearest explanation I found, and has some great anecdotal bits at the end, including a possible link to Alfred Hitchcock's movie "The Birds".  I have always been a bit partial to the movie because it was filmed in and around the area where I grew up.