Salmon generally spawn in gravel beds in the extreme reaches of the Columbia and other large river systems on their return from the ocean - often hundreds of miles upstream from the river's mouth. After spending three to four years at sea chinook salmon return to spawn in the streams in which they were born and then to die. The South Fork of the Salmon River and the streams that feed it in the mountains of central Idaho are one such location.

River environment is critical in terms of both the development of salmon eggs and fry as well as the salmon's migration to the sea. This environment has changed for salmon returning to the South Fork over the last century and a half - changed in ways that have contributed to large decreases in the chinook population. Dams have obviously been the largest factor. They create barriers to fish both upstream and down. However, other factors have also played an important role. These include increased commercial fishing in the Pacific and in the river itself, changes in water temperature as a result of water pooling behind dams, and changes in water clarity brought about by both naturally occurring and man-made siltation. Fire, logging, mining, farming, and road construction and use have all contributed to increased silt in the rivers and streams of the Columbia system.