I'm still looking for Champ on Lake Champlain! I always have a camera with me so I suppose I'll never luck out and see him (or her).
There was a real Lake George, NY monster, Georgie. It was built by a local and moored submerged in the lake out in front of his deck. When he had folks visiting from the city, he'd have an accomplice let it rise up to the surface for a "sighting". I think it is in the Blue Mt. Lake Museum...
I just finished reading a non-fiction fishing book in which the author mentions seeing a "monster" in a small mountain trout pond. He is not the type that believes in monsters, UFOs, etc, and was absolutely shocked and astounded when he saw it. As he watched it, he eventually realized it was a family of otters swimming in a line, equal distances apart. It looked very much like a giant serpent; enough to fool him for a moment or two.
Edit: The Lake George monster was crafted by famous painter Harry Watrous of Hague, on Lake George. It is currently in the West Museum in the Hague Town Hall. Wikipedia has an entry with the whole story.