Let's not forget the Pinnipeds, too. They have been responsible for some beach closures, as have geese.

While Keta's comment about human poop is funny, DNA analysis on the fecals often shows it is cat, dog, etc. One of the more embarrassing uses of the DNA analysis was when regulators were pointing fingers at dairies for fecal contamination in a river, the real culprit was the elk herd.

Apparently, each type of mammal and bird harbors different E. coli.