Montana's trout rivers are mostly freestones, and the two exceptions, the Missouri below Holter Dam and the Bighorn below Yellowtail Dam, are what keep the state fishable while everything else is brown with snowmelt. That is the key to planning here. Late May and June are runoff on the Madison, Yellowstone, Big Hole, Gallatin, Blackfoot and Bitterroot; the tailwaters carry those weeks, and then the freestones come into shape in late June or early July and stay good into October. Montana also has fish that most states do not: Arctic grayling in the Big Hole, westslope cutthroat across the western third of the state, and bull trout in the Flathead and Clark Fork drainages.
The Madison and the Salmonfly
The Madison River runs from Quake Lake to Ennis as a long, fast riffle that fishes well from a drift boat and from the bank, then slows below Ennis Lake toward Three Forks. The Salmonfly emergence in June is the famous event, followed by Golden Stoneflies into July, caddis through the summer evenings, Tricos in August and September, and crane flies in September and October. Ideal flows run around 800 to 4,000 cfs on gauge 06037100. Big orange Stimulators and Sofa Pillows in #4 to #8 carry the stonefly weeks; Sparkle Duns and Parachute Adams in #16 to #20 cover the mayflies. Hebgen Lake upstream is a trophy stillwater with gulper rainbows and browns sipping Callibaetis in summer.
The tailwaters: Missouri below Holter, Bighorn below Yellowtail
The Missouri below Holter Dam
The Missouri River from Holter Dam through Craig to Cascade is a big, slow, weed-rich tailwater that behaves like an oversized spring creek. Sowbugs and scuds feed the fish all year, midges and Blue-Winged Olives run through the cold months, Pale Morning Duns arrive in June and July, caddis in the evenings, and the Trico spinner falls of July through September are the reason the river has a reputation. This is #18 to #24 fishing: Zebra Midges, Jujubee Midges, RS2s and CDC Baetis emergers, fished on long leaders to rainbows that are hard to fool and hard to land. Flows of 2,000 to 15,000 cfs are all fishable; the river is rarely blown out.
The Bighorn below Yellowtail Dam
The Bighorn River at Fort Smith is the other great Montana tailwater and, like the Missouri, a sowbug and scud river with heavy rainbows and browns. Blue-Winged Olives run from fall through April, Pale Morning Duns in June and July, caddis through summer, and Tricos from July into October. The upper thirteen miles from the Afterbay to the Bighorn access are the core water, floated in a drift boat and waded at the launches. The river flows through the Crow Reservation, and access rules on tribal land are specific; stay in the river channel and at the state access sites.
The Yellowstone and Paradise Valley
The Yellowstone River is the longest undammed river in the lower 48, and it fishes like it: big, fast and entirely at the mercy of snowmelt. From the park boundary at Gardiner through Yankee Jim Canyon and Paradise Valley to Livingston, it holds Yellowstone cutthroat, rainbows and browns. The Salmonfly hatch in June often coincides with peak runoff, so it is a gamble; the reliable fishing starts when the river drops in July, and grasshoppers along the banks in August and September are the best dry-fly fishing of the year. The Shields, Stillwater and Boulder rivers, all gauged tributaries, are worth exploring and do not have guide pages yet.
The Big Hole, the Gallatin and the Jefferson drainage
The Big Hole River from Wisdom to Twin Bridges is a Blue Ribbon freestone and the last river in the lower 48 with a native, river-dwelling population of Arctic grayling. The Salmonfly hatch in June is one of Montana's best, and the river gets hot and low in August, when Montana Fish, Wildlife and Parks often restricts fishing hours; check before an August trip. The Gallatin runs from Yellowstone Park through the canyon along US-191 toward Bozeman, a pocket-water freestone for rainbows and browns. The Beaverhead, Ruby and Jefferson, which join the Big Hole to form the Missouri headwaters, are gauged with temperature and are all significant trout rivers without pages here yet.
Western Montana: the Missoula freestones and the Flathead
Blackfoot, Bitterroot, Clark Fork and Rock Creek
Western Montana's fishing is arranged around Missoula. The Blackfoot is the river from the Norman Maclean story, restored and now a solid rainbow, brown and cutthroat fishery. The Bitterroot runs north from Darby through Hamilton to Missoula with an early Skwala stonefly in spring, then Salmonflies in June and hoppers from July. The Clark Fork flows through downtown Missoula and is fished right in the city. Rock Creek, east of town, is a wilderness freestone with westslope cutthroat and a Salmonfly hatch that peaks in late May and June. All four follow the same calendar: runoff in May and June, prime from July, and low, warm water in August that can trigger afternoon closures.
The Flathead, bull trout and the northwest
The South Fork of the Flathead runs through the Bob Marshall Wilderness and holds westslope cutthroat and bull trout in water most anglers reach by trail or pack string. Flathead Lake is the largest natural lake in the West; Georgetown Lake near Anaconda is shallow, weedy and one of the best chironomid lakes in the state. The Kootenai, Swan, Yaak and Thompson rivers in the far northwest are gauged and largely unwritten here.
Before you go
Montana's regulations change by river and by season, and summer heat restrictions can close afternoon fishing on specific rivers with little notice. Confirm everything with Montana Fish, Wildlife and Parks. Waters inside Yellowstone National Park require the park's own permit. For all gauged rivers in the state see the Montana fishing hub, and for the trout detail the Montana trout page.