Alligators in the Sewers

It was once a fad among New Yorkers vacationing in Florida to bring back baby alligators for their children to raise as pets. These infant gators eventually grew up and outlived their cuteness, sad to say, at which point their desperate owners flushed them down the toilet to get rid of them. Some of these hastily disposed-of creatures managed to survive and breed in the dank Manhattan sewer system, so the story goes, producing colonies of giant, albino alligators beneath the streets of New York City. Their descendants thrive down there to this day, completely hidden (apart from the rare heart-stopping encounter between sewer gator and sewer worker, that is) from human eyes

citation: http://urbanlegends.about.com/od/alligators/a/sewer_gators.htm