The movie came out in 1980:
Alligator
“In 1968, a teenage girl purchases a baby American alligator while on vacation with her family at a tourist trap in Florida and gives it the name Ramon. When the family returns home to Chicago, the girl’s surly, animal-phobic father promptly flushes it down the toilet and into the city’s sewers.
The baby alligator survives by feeding on the discarded carcasses of animals used in illegal experimentation and dumped into the sewers. These animals had been used as test subjects for an experimental growth formula intended to increase agricultural livestock meat production. However, the project was abandoned because while the formula had the desired effect of making the animals larger than normal, it had the unwanted side effect of massively increasing the animals’ metabolism, causing them to develop an insatiable appetite.”
https://en.wikipedia.org/wiki/Alligator_(film)
It was a bad movie. I remember a group of boys playing pirate making a younger boy walk the plank (diving board) at a party. We started crying when they were about to push him into the water. He saw the alligator, but they didn’t.
The movie had limited character development because the alligator would eat them too soon. Definitely not a Jaws quality movie.