Alligator

Alligator is a 1980 American horror thriller film directed by Lewis Teague from a screenplay by John Sayles, and starring Robert Forster, Robin Riker, Michael V. Gazzo, and Dean Jagger. It also features appearances by Jack Carter, Sydney Lassick, Perry Lang, Angel Tompkins, Henry Silva and Sue Lyon in her last screen role. 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.

Synopsis from Wikipedia, CC BY-SA 4.0. Everything below written here.

Poster © the film's rights holders.