Northern Idaho is narrower and often forested; southern Idaho includes broad valleys and the Snake River Plain. is the correct choice. The mountainous northern and central areas differ from the larger irrigated valleys of the south.

Rivers connect mountain snowpack, valleys, ecosystems, farms, and communities. Seasonal runoff helps replenish waterways, while reservoirs and diversion structures change how water is available. River management therefore involves tradeoffs among agriculture, energy, habitat, and recreation.