Dark Tide.

Andi joins her husband Tim on a tropical island to help him with the capturing of poisonous sea snakes for their venom. Her flagrant sensuality attracts the attention of hired hand Dak, and when Tim becomes bitterly obsessed with his faltering job, Andi shares an intimate afternoon with the obsessed crewman, but then refuses to continue the affair, which leads the jilted lover to begin a series of escalating violent events.