A sewer alligator is an urban legend and myth centered around alligators which lives in sewers, in areas which an alligator would not typically be found in, such as New York City or Paris. These accounts are mostly fictional and are rare to encounter. Stories date back to the late 1920s and early 1930s; in most instances they are part of contemporary legend.

Alligator is a 1980 American independent horror film directed by Lewis Teague and written by John Sayles. It stars Robert Forster, Robin Riker and Michael V. Gazzo. It also includes an appearance by actress Sue Lyon in her last screen role. Set in Chicago, the film follows a police officer and a reptile expert who track an enormous, ravenous man-eating alligator flushed down the toilet years earlier, that is attacking residents after escaping from the city's sewers.