Norway's salmon farms have a parasite problem, and it is spilling into the open sea. Salmon lice bred in the crowded open-net cages of roughly 1,000 farming facilities are infesting wild salmon as they migrate between rivers and ocean, and the film follows the people trying to measure and stop the damage. Aquatic biologist Helge Skoglund dives into freezing rivers each autumn to count returning fish for the government; the wild population has dropped from over a million to under 400,000, closing many rivers to fishing entirely. The Norwegian Seafood Council puts average farmed-fish mortality at around 17 percent, a number the film uses to show how deep the crisis runs inside the industry itself. Salmon farmer Thomas Myrholt offers a possible fix: closed tanks sealed off from the open sea that he says keep his stock lice-free, and he is pushing for regulation to make that approach standard. Fishermen, scientists, and farmers each get to make their case for what happens to Norway's rivers next.