The Middle Fork of the Flathead River is born in the high, rocky country of western Montana, near the roof ridge of North America. For dozens of miles it rolls through green wilderness, taking in the snowmelt from Muskrat Pass and Slippery Bill Mountain and a half dozen creeks as it grows into one of the beloved waterways of the American West.

On a warming midsummer morning, the waters curled like a cat around the shins of a short woman wearing polarized sunglasses and a trucker’s hat pincushioned with fishing flies. Hilary Hutcheson is a fly-fishing guide and climate activist who speaks to audiences across the nation. Her summer fishing season in western Montana is brief, which means frenetic, and by