After Dionne bribes tour guide Rodrigo to see "Big Ben," they find the massive alligator dead and torn in half. The hippo ambushes the boat, capsizing it and injuring Rodrigo. As the group scrambles onto trees and debris, the hippo systematically hunts them down.
Tragedy strikes the family group when grandfather Tim and his teenage grandson Mikey are picked off by the hippo. Overcome with grief after witnessing her father and son die in quick succession, Sally falls into a catatonic state and willingly surrenders herself to the creature.
Walker arrives on a small motorized boat to rescue the survivors, but his boat runs out of fuel. Walker, Sistine, and Dionne row to an abandoned alligator facility in the swamp. There, they discover old records confirming that the facility was secretly used decades ago to breed imported hippopotamuses under the scrapped 1910 American Hippo Bill initiative.
Outside, Sistine discovers a baby hippo calf trapped under heavy rusted iron fencing. Realizing the mother hippo's territorial fury was driven by protecting her trapped calf, Sistine works to free the baby hippo. Once freed, the calf reunites with its mother in the water. Recognizing that the human threat has de-escalated, the mother hippo leaves with her calf into the bayou. Walker, Sistine, and Dionne ignite the facility to signal a rescue helicopter, which picks up the surviving women as dawn breaks over the swamp.