The Boise River is a 102-mile-long tributary of the Snake River in the Northwestern United States. It drains a rugged portion of the Sawtooth Range in southwestern Idaho northeast of Boise, as well as part of the western Snake River Plain. The watershed encompasses approximately 4,100 square miles of highly diverse habitats, including alpine canyon…The Boise River is a 102-mile-long tributary of the Snake River in the Northwestern United States. It drains a rugged portion of the Sawtooth Range in southwestern Idaho northeast of Boise, as well as part of the western Snake River Plain. The watershed encompasses approximately 4,100 square miles of highly diverse habitats, including alpine canyons, forest, rangeland, agricultural lands, and urban areas.