I assume you are familiar with Monster Quest. One of the only episodes that found anything like proof (aside from giant squid) was regarding Champ. They found evidence that SOMETHING in the lake was using echolocation--the RADAR used uniquely by bats and water-bound mammals like whales and dolphins. Perhaps Champ is an ancient variety of whale? there have been fossilized remains of small whales found nearby from whe Champlain connected with the Atlantic.