Bighorn River Fly Fishing

Bighorn River MT

The Bighorn River, nestled in the heart of south-central Montana, is a renowned tailwater fishery. Anglers often begin their journey along this iconic river as it emerges from the Yellowtail Dam on the Crow Indian Reservation near Hardin. The stretch of river encompassing the initial 13 miles downstream from the dam represents the most frequented and heavily fished section.

Beneficial Features of the Bighorn

Here is why Bighorn River is such a great river.

Number of Trout

  • 5000 trout per mile – the initial 13-mile stretch below Yellowtail Dam boasts an average of over 5,000 catchable trout per mile according to biologists from the Montana Department of Fish, Wildlife, and Parks (MDFWP).
  • Some local guides believe their actually more trout than that.
  • This number is nearly double the catchable trout per mile compared to most other trout streams in Montana.

Size of the Trout

The remarkable aspect doesn’t stop there; it extends to the average size and growth rate of the trout in the river. A 6-inch rainbow trout in the spring can easily grow to be a 12-inch fish by the fall.

Furthermore, the typical four-year-old fish in the Bighorn River reaches an impressive length of approximately 20 inches and possesses a robust and well-built physique. These statistics are not isolated cases but are supported by H. R. Stevenson’s master’s thesis from Montana State University, which sets the standard for the river’s fish quality, showcasing that numerous trout in the Bighorn River attain these impressive sizes, with some even reaching significant proportions.

Good Flows & Temps

The Yellowtail Dam, combined with the region’s relatively moderate year-round climate allows for fly fishing opportunities for a substantial portion of the year. Yellowtail Dam’s construction was completed in 1967, and uniquely, it features an afterbay that effectively regulates peak-power-demand releases from the dam. This ensures consistent river flows and moderates water temperatures, making it an ideal habitat for trout to thrive.


Another contributing factor to the river’s prosperity is its high alkalinity, with pH levels typically ranging from 7.4 to 7.8. This favorable pH environment fosters an abundance of freshwater invertebrates, creating a thriving ecosystem in the Bighorn River. As the river meanders across the Bighorn Basin from northern Wyoming, it eventually winds its way through deep limestone canyons. Throughout this journey, the river continuously benefits from the enriching properties of the limestone rock through which it flows.

Cold Water

Before the construction of the dam, the Bighorn River was essentially a prairie river, primarily inhabited by various warmwater fish species. Small populations of brown trout could be found near the mouths of certain feeder streams, although brown trout were never intentionally introduced to the Bighorn. It is speculated that the current substantial brown trout population may have originated from this initial small group.

Great Management

With the creation of the new reservoir resulting from the Yellowtail Dam, the Montana Department of Fish, Wildlife, and Parks (MDFWP) initiated an extensive stocking program. This effort involved releasing 105,000 cutthroat trout and 500,000 rainbow trout into the river. Over the years, hundreds of thousands more rainbow trout were introduced, although the stocking of cutthroat trout ceased in 1972. Initially, the rainbow trout stocked were of the Arlee strain from the Arlee, Montana, state hatchery. However, the Arlee strain, which spawns in the fall, was not well-suited for the Bighorn environment. Subsequently, the Arlee strain was replaced with a lineage of rainbow trout that exhibited spring-spawning behavior, and this strain has proven to be highly successful in competing with the prevalent brown trout population in the river. The last batch of rainbow trout was introduced in 1986, and the Bighorn River now thrives with this thriving, spring-spawning rainbow trout strain.


The river flows through the Crow Reservation, where tribal regulations take precedence. In general, anglers are required to stay within the river channel below the high water marks, unless specific areas allow otherwise. For those looking to wade into the river, access can be somewhat limited, with three primary launch areas available: the afterbay, the 3-mile access point, and the Bighorn or 13-mile takeout further downstream.

Floating the river in a drift boat, raft, or canoe is highly recommended due to its ability to provide access to prime fishing spots. However, it’s worth noting that you don’t necessarily have to spend your entire day fishing from the boat, although some anglers choose to do so. One approach would be stopping to wade whenever there are rising fish or a particularly enticing section of water. The Bighorn River’s riverbed is conducive to wading, making it relatively easy to navigate. Exploring the various side channels and the back sides of islands can be fun as some of the best opportunities often hide in unexpected locations.



Midges in Spring

The Bighorn’s fishing season kicks off early, with increasing activity by St. Patrick’s Day as temperatures rise. During this period, a close examination of the water reveals a significant presence of midges, numbering in the millions. These midges are among the handful of insects that make up 87 percent of the river’s invertebrate life.

The abundant midge hatches on the Bighorn result in extended surface feeding activity among the fish, but they present a challenge. Adult midges often cluster together, and the fish eagerly consume these swarms. Overcoming this challenge requires a light tippet, precise presentation, and confidence in your choice of fly pattern.

Consider a cluster midge pattern tied on a #16-18 hook with some sort of visibility like a parachute wing. Other effective patterns for this hatch include subsurface midge pupae, Griffith Gnats, and small Parachute Adams.

Midges in Winter

Montana winters can certainly deliver bone-chilling cold, but thanks to the Bighorn being a tailwater, its trout remain active and feeding throughout the year. Many seasoned Bighorn anglers keep a close eye on the weather forecasts, seizing the opportunity to fish when temperatures rise above freezing. During the winter, most anglers focus on the first 3 miles below the dam, although the river remains open for fishing all the way down to the Bighorn Access point, 13 miles downstream. For optimal results, consider working a streamer slowly across a deep, slow pool or using small midge patterns for nymphing.

During both the onset and conclusion of the winter season, midge hatches become quite abundant. In November and once again in March, the weather can become tolerable, sometimes even pleasant. During these periods, the fish surface to feed, making them receptive to carefully presented dry flies like the Griffith’s Gnat or other midge cluster patterns.


As spring progresses, another noteworthy insect emerges: the Baetis, also known as the Blue-winged Olive. This is considered a “super-hatch,” attracting anglers from all over the country to the Bighorn. While Baetis populations can vary from year to year, abundant years offer exceptional fishing experiences. Blue-winged Olives thrive in inclement weather conditions, making cloudy, rainy, or even snowy days ideal for dry fly fishing success. If the fish are not taking the dun, try suspending a small #18 Pheasant Tail nymph below your dry fly, as the trout may be selectively targeting emerging nymphs.


Most years, PMDs show up between July 15 and August 1. When the hatch is on, the dry-fly fishing can range from incredible to incredibly frustrating. A realistic PMD Dun will catch fish by the dozens one day, and get nothing but refusals the next.

Avoid becoming too fixated on a single fly or technique that worked well in the past. Trout behavior can vary throughout the day and during different stages of a hatch. Be prepared by carrying PMD nymphs, emergers, duns, and spinners in your fly box, and adapt your approach as you observe what the trout are feeding on.

As PMDs and stoneflies begin to diminish, the emergence of Black Caddis becomes a remarkable sight due to their sheer abundance. These caddis actively swim to the surface to hatch and return to the river bottom to lay eggs, often leading to simultaneous hatching and mating flights during late afternoons and evenings.


To imitate swimming caddis, try swinging a small soft hackle wet fly through the riffles. However, many anglers prefer targeting rising trout in slow eddying waters along the banks.

For hatching adults drying their wings, opt for patterns like CDC Black Caddis that ride high on the surface. During mating flights, focus on imitating dead, spent adults congregating in back eddies, using low-riding patterns such as the Henryville Special or Mike Lawson’s Spent Partridge Caddis for optimal success.


Mastering the Trico hatch on this river presents a unique challenge due to the abundance of natural insects on the surface. Often, your fly will be just one of many in a trout’s view. So, what makes your fly stand out? Many anglers persistently cast, hoping for a chance.

While this approach can yield results, there are tactics to enhance your success. First, understand that most fish have a rhythm. They don’t strike at every passing fly. Some may feed every two seconds when they’re particularly hungry, but most have a slower rhythm, breaking the surface every 5 to 30 seconds. By closely observing each fish and discerning its rhythm, you can anticipate when it will rise next. Well-timed casts can significantly increase your chances, possibly by 200%.

Tricos persist into the fall, though dry-fly fishing can decline due to reservoir turnover, resulting in turbid water discharge. This phenomenon occurs when the lake’s surface cools in autumn, causing colder water, along with accumulated weeds and algae, to sink and pass through turbines, muddying the otherwise crystal-clear Bighorn. Turnover typically happens in September or early October when night temperatures drop below freezing. Fortunately, turbid water doesn’t occur every fall, and when the river is clear, it’s a delightful time to fish.

As November approaches, the river clears up, and the fish start rising to Autumn Baetis or midges. For some anglers, this marks the season to use their “big rod” and work the long runs above and below the weed beds, casting sizable streamers as far as their strength and technique allow.

The Wyoming Section

Bighorn River Wyoming
Bighorn River in Wyoming

Wyoming’s Bighorn River offers giant trout without the crowds because is not as well known or pressured as the Montana section. Yet it ranks close to it’s Montana neighbor. Though it doesn’t hold the numbers of fish as the Montana section does, it still is reported to hold close to 2000 fish per mile.

Lost of Big Fish

The Wyoming section of the Bighorn consistently produces big rainbows and browns. In fact, the Wyoming section offers a better opportunity to catch some really big fish. Unlike the Montana section you can fish the Wyoming Bighorn river in relative solitude.

Wyoming’s Bighorn flows through the North central part of the state. The river runs near the towns of Greybull, Worland and Thermopolis.

A Medium Sized Stream that is Accessible

The Bighorn in Wyoming is a medium sized stream that begins at the Wedding of Waters, below the Wind River Canyon near Thermopolis.

Fishing is great through Thermopolis and down stream for about 20 miles. Through this prime stretch there is plenty of access to the river. With eight boat ramps and some places with 100 foot easements along the banks, there is plenty of access for both float and wade fly fishing.

Catch browns, rainbows and cutthroats

The Bighorn river holds wild, naturally spawning brown trout as well as cutthroat and rainbow which are stocked by the Wyoming Game and Fish. Rainbows and cutthroat will average between 12 and 16 inches. Since these fish don’t get the pressure that their northern neighbors do, they are not bashful.

If you crave the excitement of fly fishing for big browns, this 20 mile section of the Bighorn is excellent for 20 inch browns. Brown trout from 3 to 5 pounds are common here.

The Bighorn is different from most tail waters because it’s flows stay fairly constant in the summer. This is because Boysen Reservoir is drained for irrigation. The flow will start to increase to handle spring runoff in late April and by mid July become steady again.

During the late summer the river grows quite a bit of moss and is best fished with nymphs. Some of the most popular patterns are sow bugs, prince nymphs, hares ears and pheasant tails. In August and September fish can be caught as they rise to pale morning duns, tricos and caddis. Good dry fly fishing will run into October. Streamers will also draw strikes from big fish in August extending through winter and into spring.

Hatch Chart

InsectSizeBegin DateEnd DateBest Time
Scud14-181-Mar30-Novmorning and evening
Midge16-221-Mar15-Junafternoon and evening
Baetis16-221-Mar15-Julafternoon and evening
Caddis12-1615-Apr15-Octmorning and evening
Green Drake10-121-May15-Junafternoon
Terrestrials14-1614-Jun15-Octmorning and afternoon
PMD16-1815-Jun30-Sepafternoon and evening
Little Yellow Stone12-1415-Jun15-Sepmorning and afternoon
Midge16-2215-Sep30-Novafternoon and evening
Baetis16-2215-Sep30-Novafternoon and evening

Wyoming’s Bighorn River may never be as popular as the Montana section of river with the same name. Yet it has large numbers of trophy trout ready to be taken in relative solitude. The Bighorn river in Wyoming may get little publicity but it is truly one of Wyoming’s blue ribbon streams.

How to Book

Fly Fishing the Bighorn River: Hatches, Fly Patterns, Access, and GuidesGÇÖ Advice
  • Galletta, Steve (Author)
  • English (Publication Language)
  • 240 Pages - 07/15/2015 (Publication Date) - Headwater Books (Publisher)
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