''The River Why'' is an adaptation of the 1983 Sierra Club novel by David James Duncan. The coming-of-age tale centers on a young man named Augustine "Gus" Orviston (Zach Gilford) and his quest for an elusive Rainbow Trout, which is a metaphor for his internal search for self-knowledge. Amber Heard plays his love interest, a tomboy fly-fisher named Eddy.