Three spring creeks-Nelson, DePuy, and Armstrong-rise on private ranchland and feed the river. They are loaded with fat (14- to 20-inch) brown, rainbow, and cutthroat trout that feed all day on lavish hatches of midges and pale morning dun, sulfur, and blue-wing olive mayflies. It's year-round fishing, though July and August are prime time. The ranchers preserve the quality of the angling by enforcing fly-rod-only, catch-and-release regulations. They charge a modest fee and restrict the number of anglers. You can book a day of fishing through most of the many outfitters in the Livingston and Bozeman area.