Deadly Species (2002)

Wealthy big game hunter, Wilson Frields, funds an expedition going deep into the Florida Everglades to search for the Calusa: a lost tribe of Native Americans. When the team discover the gruesome remains of another expedition, Friels admits he is searching for the Calusa's Fountain of Youth and its guardian, a mythical and deadly beast. As they delve deeper into the Everglades, the bloodthirsty beast begins to stalk and kill members of the group and, in one struggle, their leader Brinson Thomas is injured and begins to metamorphose into a creature himself. His only hope: to drink from the waters of the Fountain. The terrible truth behind the Calusa must be discovered if any of them are going to get out of there alive!