I wonder if other eagles ever do this? Maybe a distant Golden Eagle swimming in a Scottish loch might be mistaken for a large aquatic creature of some kind - Nessie? Birds are dinosaurs, after all..
As for nessie, I'm not sure there are any outstanding 'unexplained' photos (the 'surgeon's photo' is much like the famous bigfoot film - it's been admitted to being a hoax, but 'true believers' insist that that's just the person being coerced into a cover up)