About 100 miles from the ocean, a young woman is preparing to swim in a calm river, though she has to consider the threat of bull sharks lurking beneath the surface. Nearby, Kate, a local ranger, is investigating reports of a significant drop in water levels. Her colleague Mark dives in to explore but suddenly stops responding to her radio calls, prompting concern from Kate. It turns out to be a prank, as Mark resurfaces, claiming he saw a giant alligator, much to Kate's annoyance.