The Gardner is a steep, pretty little Park freestone that drops fast from the high country down to meet the Yellowstone at Gardiner, and it punches well above its size. The upper reaches above Osprey Falls hold native cutthroat in genuine backcountry; the lower canyon below Mammoth runs brown trout and rainbows in pocket water you scramble to reach. There's geothermal water feeding in near the old Boiling River, which colors the temperature picture. It's a hike-and-wade, read-the-pockets sort of river, and the cutthroat up top are worth the climb.

• Mixed