The Shark Men

A group of tourists head into an uncharted region of Brazilian forest. Beyond a fence of jungle vegetation they discover a concrete island in the center of an artificial lake. Using a derelict boat to cross the murky water, they are attacked by ravenous aquatic predators. An elderly stranger appears, taking the survivors into his secret fortress, a former military research station. He reveals that he has created a breed of half man, half shark mutations, and his guests will be fed to the specimens to satisfy their hunger.
The tourists imprison the deranged scientist and seek a means of escape. But can they survive against creatures who possess the most lethal traits of shark and man?