Survivors live on makeshift floating communities called "atolls" or on individual boats, scavenging for resources like "dirt" (highly valuable soil) and fresh water.
The Mariner reluctantly helps a woman named Helen (Jeanne Tripplehorn) and a young girl named Enola (Tina Majorino). Enola has a map to "Dryland"—a mythical last piece of land—tattooed on her back.
Kevin Costner stars as The Mariner , a solitary, nameless drifter who has mutated to survive in this environment, possessing gills and webbed feet.