Island Park Reservoir

Island Park Reservoir holds the Henry's Fork above Box Canyon, at about 6,300 feet in the lodgepole country west of Yellowstone. It covers about 7,300 acres when full, and it is an irrigation reservoir first: the level drops through the summer, and in a dry year it falls far enough to leave the upper arms and the McCrea Bridge area out of reach by August. What comes out the dam is the cold water that makes Box Canyon below.

It fishes as a stillwater for rainbows, kokanee and brook trout. In June and early July the shallow west end and the arms warm first, and fish feed on chironomids, damsels and callibaetis in the weed beds; a float tube on a calm morning is the classic way to fish it. Later in summer the fish follow the cool water down and toward the dam, and in fall the brook trout color up and move shallow. Ice fishing near the dam is popular in winter. There are no special rules: Idaho's general limits apply.