Beginning at Boysen Reservoir in Wyoming, the Bighorn enters Montana more than 150 miles downstream, where it flows into Bighorn Lake, formed by the Yellowtail Dam. Below the dam, the river flows through an isolated landscape as a tailwater stream, traveling through the Bighorn Canyon National Recreation Area for the first twenty miles. After flowing through the Crow Reservation for twenty-eight miles, the Bighorn River continues northward towards the confluence with the Yellowstone River near Bighorn, Montana.
The Pryor Mountains and the smaller Bighorn Mountains backdrop the valley and stream throughout. There are many rock cliffs with scattered trees for the terrain. Along the bank, there is a mix of grass, cottonwood trees, and a variety of brush to provide adequate cover for trout. The river consistently pulls out large fish. Brown trout average around fifteen inches, while rainbow trout average around sixteen inches. The abundance of trout in the Bighorn is one reason many anglers fish here – it is a proper blue-ribbon trout stream. The Bighorn River is known for holding the most consistent population of thriving wild fish. Fishing for trout on the Bighorn River is best within the first 13 miles of tailwater below the dam. There are estimates that fish populations on this upper stretch hold between 3000-5000 fish per mile. A large quantity of these fish average fourteen inches in length. The rich fertility of the Bighorn River as a tailwater with crawling mayflies and abundant hatches allows the trout to grow at a steady rate.
With great hatches year-round, including midges, blue-winged olives, caddis, and some golden stones, the Bighorn fishes well throughout the year. Its best fishing season is in May and June. Nymphing is one of the most productive ways to fish the Horn, although fishing light tippets and dry flies provides technical and fun fishing. Something most don’t know is that it can be a great winter fishery nymphing and fishing streamers in and around deep pools. Usually, it is fished with very consistent patterns like rubber legs, worms, pheasant tails, and other attractor nymphs. Although when a hatch is popping, double dry fly rigs when the fish are rising give them a variety to choose from. As the river progresses much further downstream, irrigation begins to pull a good portion of water, making the stream slower and a tad warmer. Big browns can handle these warmer water conditions, even though anglers may not find them in great numbers. The trophy-sized fish tend to lurk alone.
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Sections of the Bighorn River
After (Yellowtail Dam) to Bighorn Access Site
This section of the Bighorn is possibly one of the most famous fly fishing sections of river in the state. The Yellowtail Dam regulates river flows coming out of the reservoir. A huge plus is that demand for irrigation does not highly impact the flows. As a result, the Bighorn River is almost always cool, which couldn’t be better for aquatic insect life and trout. Beginning in April, anglers can target rainbow and brown trout during prolific hatches of blue-winged olives during periods of warm weather. The perfect time to be on the Bighorn to experience this hatch is when you have an overcast day coupled with warmer temperatures.
In the early summer, much like other tailwaters and freestones across the state, the Bighorn has a yellow sallie hatch. A yellow sallie is a small stonefly that can be well represented using size 14-18 yellow stimulator flies. Like many other stoneflies, yellow sallies prefer clean water, and unlike caddis and mayflies, they will crawl out of the water and onto rocks to hatch.
Later in the summer, the Bighorn experiences hatches of pale morning duns. Anglers can fish the hatch during the late morning hours, and the spinner falls in the evening. But what the Bighorn is most famous for is the caddis hatches in August. Be prepared to bring an assortment of caddisflies with you if you’re planning to fish the river in August! Like the Missouri River and the Madison, the caddis will likely be most active in the evening during the summer months.
By September, hatches of tricos, a small (size 18-22) mayfly, begin to hatch in the section below the dam. This can bring pods of fish to the surface to slurp and pick off this array of mayflies. For the angler, it can provide an exceptional dry fly fishing challenge. Light tippets, long leaders, and precise casting are required to manage the microcurrents.
Bighorn Access Site to Yellowstone
Thirteen miles below the dam is the Bighorn Access Site. At this point, the current begins to slow down the closer the water gets to the Yellowstone River. Temperatures start to increase on the lower river due to the water’s distance from a cold water source. In addition, irrigation starts pulling water from the Horn. Trophy-sized brown trout tend to be caught in this lower section. There is excellent fishing between the Bighorn Access and Two Leggins Access sites, but the trout population is nothing like the first thirteen miles below the dam. This is a great streamer section in the fall to target a potential trophy. Below the Two Leggins Access Site, anglers can still target trophy brown trout during the spring and fall; but the numbers will continue to decrease. This section turns into a warmwater fishery during the warmer months and offers fly fishing opportunities for catfish and bass.
Seasons on the Bighorn River
During the winter, midges are a go-to. The slower pools, runs, eddies, and calm water is best. Midges don’t tend to hatch as well in faster-moving water as a PMD would. Nymphing midges in deep pools and long runs are a great bet, just like fishing them on the surface during a warm winter day. Long well-tapered leaders for the midge dry flies and nymphs are a must. As a tailwater, there are many assortments of larvae, and one of them is a red worm. San Juan Worms imitate the red worms found in the Horn’s aquatic buffet.
Spring run-off does occur when the reservoir fills. Flows are managed, but sometimes the fishing can be hit-or-miss in early June. In July, the Horn experiences hatches of yellow sallies and even a handful of golden stoneflies.
With warmer weather leaving the winter and spring, the blue-winged olives begin hatching in healthy numbers. From the beginning of April to June, anglers that prefer dry fly fishing will fish baetis. These bugs love to hatch on warm, cloudy days.
During the late summer, the Bighorn River experiences prominent hatches of pale morning duns and caddis that last throughout July and August. The PMD hatch generally occurs during the late morning hours or the middle of the day in the heat. After PMD’s, the caddis follows and hatch well into August. Caddis activity is most prominent during the late evening hours.
Hatch after hatch, bug after bug. Fall brings tricos. Early in the morning and late in the evening is the best time to fish Tricos. Much like midges, utilizing long leaders and light tippets is necessary to present small dries in microcurrents. Hatches of tricorythodes can bring up pods of fish and large singles.
Popular Bighorn River Flies
- X-Caddis (size 14-18)
- Sparkle Dun (size 14-20)
- Foam Beetle (size 12-16)
- Rusty Spinner (size 14-20)
- Last Chance Cripple (size 14-18)
- Buzzball (size 16-18)
- Yellow Stimulator (size 14-18)
- Captive Dun (size 14-18)
- Griffith’s Gnat (size 16-20)
- San Juan Worm (size 14-18)
- Pheasant Tail (size 14-20)
- Hare’s Ear (size 14-20)
- Two Bit (size 14-18)
- Zebra Midge (size 14-22)
- Prince Nymph (size 14-18)
- Galloup’s Barely Legal – olive/white (size 4)
- Galloup’s Dungeon – olive, black, white, yellow (size 4-6)
- Home Invader – black, white, olive, yellow (size 6)
- Bow River Bugger (size 4-6)
- Sparkle Minnow Sculpin (size 4-8)
Bighorn Angler – Unquestionably one Montana’s most famous trout rivers, fly fishing the Bighorn River is on every angler’s bucket list. Its trout-filled waters flow from the base of the Yellowtail Dam in Fort Smith, Montana and abundant insect hatches produce exceptional rainbow and brown trout fishing almost year-round for both novice and expert anglers alike. With a team of the most hardworking and courteous guides in Montana, the Bighorn Angler is second to none when it comes to outfitting, having offered high-quality fly fishing packages for over 30 years. Their wide array of lodging options, top-notch guide service, and home cooked meals are the perfect ingredients for the ultimate Bighorn River fly fishing experience. You will also find a fully-stocked fly shop with knowledgeable and courteous staff on-site.
Bighorn River Lodge – Montana’s Bighorn River Lodge has drawn avid fly fishing enthusiasts and sportsmen alike for decades. Known as one of Montana’s finest trout river in the country, the Bighorn River boasts an abundance of trout ranging in size from 14 to 18 inches, many exceeding 20 inches. Recent fish counts indicate an unsurpassed fish population of 5,000 trout per river mile. The Bighorn River is situated on the eastern edge of the Rock Mountains just north of the Wyoming – Montana state line. If you are looking for a Montana fly fishing vacation, this is your destination!