From Beneath.

Jason and Sam travel to visit Sam's sister at her secluded farmhouse. While waiting for them to appear, Jason is bit by a strange organism in a pond. The bite begins a transformation in Jason, and now the couple must race against time to figure out what happened to Sam's sister and her family, and what lies in store for them. All of these elements are tantamount to the ultimate fear addressed in the film, the fear of losing a loved one and worse, becoming a monster in their eyes.