This movie is based in an american town near a swamp. It is about a boy who discovers a swamp monster but is trying to convince his dad and the locals it exists. I remember a scene where he takes his friend into a garage to dress him up in a costume similar to the monster. Also a scene where they all discover it but let the creature go in to the end. I’m not sure if its a 90’s movie or 2000’s. It’s more of a family movie rather than a horror movie. Hopefully this helps and someone can remember it!