Begin where the Snake River begins, as crystal-clear, clean water on the calderas of the Yellowstone Plateau, on the edge of the vibrant national park. In late spring, the largest tributary in the headwaters, the Henry's Fork of the Snake River, is still locked in a head-high layer of snowpack. On wind-blown ridges rimming the water, hundreds of elk graze under the late morning sun. A-frames and log cabins hibernate, boarded and silent, awaiting the summer arrival of the fly fishers who treasure this place. Everything appears at peace and as it should be.
But for those who know what to look for, a less pristine reality is evident, even here in the river system's headwaters. It's represented by the 7,000-acre Island Park Reservoir on the Henry's Fork, built in 1938 to benefit farmers downhill from here by holding back and controlling the flow for irrigation diversions. This repurposing of the water becomes obvious 20 miles south of Island Park, where the plateau tips to deliver the Henry's Fork to the Snake River Plain, a rapid descent from the residue of a high-elevation winter to a more recognizable spring, from the postcard Idaho to the real Idaho, from what was to what is.
From here on, the Snake, to use the euphemism of record, becomes a "working river" – wholly subservient to agriculture. There are many ways to describe how a river system gets harnessed to ag, but we'll begin with the most basic, the dams and reservoirs. The Snake's drainage is interrupted by no fewer than 23 large dams that form reservoirs, and there are many smaller dams that divert water for irrigation without stalling the river's flow. The reservoirs impound about half of the river's 1,078 miles. None of this is news; we began damming this river – the largest tributary of the Columbia – more than a hundred years ago, and the dams were only the first step in the creation of one of the world's largest concentrations of industrialized agriculture.