Alligator (1980)

A vicious alligator named Ramon, who was flushed into the city sewer as a baby, survives to become a 32-foot-long menace who devours animals and people alike. Ramon's so huge because of the steady diet of dead pets - treated with growth hormones - that he's fed on for 12 years. Now the tremendous brute is angry and looking for revenge. Only detective David Madison knows of Ramon's existence, and it is his task to prove to the rest of the city that a tropical beast lives in their midst. Veteran screenwriter Sayles' script finds the perfect blend of comedy and horror, making this an entertaining romp through the sewers of Chicago.