An alligator lived in the sewers underneath Raccoon City. This very large mutant grew from a baby which, like the urban legends, was flushed down the toilets, fulfilling the "sewer gator" myth. This alligator became a threat to a band of survivors moving through the sewers in search of a way to the Raccoon City Underground Laboratory. It was killed when it bit into a fuel canister, and a well-targeted shot caused it to explode inside its mouth.
Another alligator residing in the Lakeside Area of the Raccoon Zoo was one of the main attractions until the virus outbreak occurred. The survivors who crossed the small lake had to deal with the monster while swimming across.
Yet two other alligators lived in the sewers of Sheena Island. Considering that the island was near Europe, this animals were probably transported as pets like the one in Raccoon's sewers.