Snake-Columbia basin streamflow

The Snake is the Columbia's largest tributary, draining about 108,000 square miles across Wyoming, Idaho, Oregon and Washington. This page lines up the two ends of it: the gage above Jackson Lake in Wyoming, which reads the unregulated headwaters before any storage touches them, and Weiser, Idaho, which reads the river after the entire Snake River Plain irrigation system has taken its share.

Together they measure development rather than only hydrology. The headwater gage shows what the snowpack produced; Weiser shows what survived the plain. The seasonal patterns differ accordingly: the upper gage runs a clean snowmelt curve peaking in June, while Weiser's summer level answers to irrigation demand and reservoir operations. Weiser is also the flow that enters Hells Canyon, so it governs hydropower on the Idaho Power system and the augmentation released for juvenile salmon on the lower Snake.