John Sayles read Frank Ray Perilli's script for the film once and then totally scrapped it. Sayles said it was set in Milkwaukee and explained that the alligator grew gigantic because of beer from a beer factory going into the sewers.
Sue Lyon is incorrectly credited as "ABC Newswoman". In fact, her character appears to be working for NBC. The microphone she uses during an interview is clearly marked with the NBC 'N' and peacock logos.
When the alligator attacks Slade's limousine and the camera is on Slade, the car is continually rocking as if being hit. When the scene shifts to the limo driver, the car is still.
When Madison enters the manhole cover at the films climax, he is wearing Adidas trainers; when he lands in the sewer he is wearing boots; when he re-appears from the manhole he is wearing trainers again.