The second of six wildlife films from around the world.

The crystal-clearwaters of the Soca river in the Slovenian Alps are home to the giant marble trout. Tonight's programme tells how local biologist Jose Ocvirk saved the marble trout from the brink of extinction. After becoming prey to starving First World War soldiers, the fish was then threatened by brown trout introduced in the 1920s. This film charts the marble trout's life from egg to adulthood, and shows how it still must battle for survival against the brown trout and a range of predators.