So is the water in the story for the link. The problem is that contaminated is not a binary function. If the material is sufficiently dispersed in the water radiation levels won't rise much (I say rise because sea water is already naturally radioactive, as most things are. Which one could say that sea water is "contaminated" but that wouldn't be useful). If it isn't sufficiently distributed then the distance between you/a fish/sea creature is going to play a big factor since water is really good at stopping radiation. Basically think about you and your wifi router. If there's a metal wall between you and the router you're not getting a signal. Attenuation is the key concept in both radiation and the wifi router. Though this is obviously the fall back for "if they mess up" which isn't likely.
