On a warming mid-summer morning at the river, the waters curled around the shins of a short woman holding a tall mug of coffee. The woman wore a trucker’s hat pin-cushioned with fishing flies and polarized sunglasses that cut the water’s glare.

Hilary Hutcheson is a well-regarded fly-fishing guide and climate activist, much in demand across the nation. Hutcheson’s main fishing season in western Montana is brief, which means frenetic, and by late July, her voice, which is lightly scuffed at the best of times, sounded as if it were being played through old speakers.