River Monsters (2009)

The eerie disappearance of three men in far eastern Russia proves to be a baffling case for Jeremy Wade. His first visit to Russia takes him on a three-day trip to the Amur River where he seeks to uncover what happened to the fisherman and others who have met their demise on these waters. The prime suspect is a predator that can top a ton and exceed 18 feet in length — yet for some reason, not a soul will help him find it. Stonewalled at every turn, Wade begins to believe there is there a dark secret he's not meant to discover.