Bighorn River Fly Fishing: Montana's Blue-Ribbon Tailwater Below Yellowtail Dam

The Bighorn River doesn't look like much from the highway. An hour south of Billings, you turn off the interstate at Hardin and drive through open grasslands on a two-lane road that dead-ends at Fort Smith, a town of about 100 people. Nothing about the landscape suggests world-class trout fishing. Then you walk down to the Afterbay and see the water: cold, clear, and teeming with sow bugs, scuds, and rising trout. The Bighorn holds over 2,000 wild trout per mile below Yellowtail Dam, fed by some of the most reliable hatches in the West. It's one of Montana's great fisheries, tucked into a corner of the state most tourists never visit.

Quick Reference

What	When	Key Numbers
Dry fly fishing	April through October	2,500-3,500 CFS ideal; BWOs, PMDs, caddis, Tricos
Nymphing	Year-round	2,000-5,000 CFS fishable; midges, scuds, sow bugs
Streamer fishing	March-April, October-November	Best on cloudy days; Woolly Buggers, leech patterns #4-8
Guided float trips	Book by March for peak season	$550-700/day for 1-2 anglers, lunch included
Fly shop	Bighorn Angler	Fort Smith, MT; 30+ years on the river
Regulations	Montana license required (no tribal permit for river)	Artificial lures only; 3 trout daily, only 1 over 18"

Why the Bighorn

The Bighorn River below Yellowtail Afterbay Dam is one of the most productive trout fisheries in the Rocky Mountain West. Cold, nutrient-rich water from Bighorn Lake creates a tailwater that supports over 2,000 wild trout per mile in the upper sections, with the 30-year average sitting around 2,200 fish per mile. Recent surveys have recorded peaks above 2,500 per mile when conditions align.

What separates the Bighorn from other Montana tailwaters is its consistency. The Afterbay Dam smooths out the hydroelectric fluctuations from Yellowtail Dam, delivering steady flows year-round. While freestone rivers across Montana blow out during spring runoff, the Bighorn stays clear and fishable. The river averages 150-250 feet in width with flows typically running 2,000-3,000 CFS, creating a broad, wadeable tailwater loaded with aquatic insects.

The fish quality matches the numbers. Brown trout regularly push 18-22 inches, with fish over 24 inches taken every season. Rainbows average 14-18 inches, with plenty of larger specimens mixed in. Both species are wild, self-sustaining populations that thrive on the river's dense food base. Local guides will tell you the pink scud is the Bighorn's secret weapon. They call it the "guide fly" because it catches fish when nothing else works. That says a lot about a river where the trout eat year-round.

River Sections

The fishable tailwater runs roughly 13 miles from the Afterbay Dam to Bighorn Fishing Access Site (FAS), with an additional lower stretch down to Mallards Landing. Public access is limited to a handful of designated sites, so knowing the sections matters.

Afterbay Dam to Three Mile Access (3 miles)

This is wade fishing paradise. Fine gravel substrate and manageable flows make the first three miles below the dam the most accessible walk-and-wade water on the entire river. Classic spots like the "Breakfast Hole," "Hot Dog Run," and "Red Cliffs" hold consistent fish populations. The cold, oxygen-rich water right below the dam concentrates trout, and you can reach productive water within minutes of the parking lot.

Floating this short section is also popular and gives better access to the prime seams along both banks.

Three Mile to Bighorn FAS (10 miles)

The heart of the fishery. This ten-mile float passes through the most productive water on the river, with braided channels, long riffles, undercut banks, and mid-river gravel bars holding feeding trout. This section is best accessed by drift boat or raft, as shoreline access between the two launch points is limited.

Most guided trips focus on this stretch, and for good reason. The variety of water types means you can nymph deep runs in the morning, switch to dry flies when a hatch comes off, and pound banks with streamers on cloudy afternoons. Pack a lunch and plenty of water. There's nowhere to stop on this float, and on a hot July day, the ten miles feel longer than you'd expect.

Bighorn FAS to Mallards Landing (13+ miles)

Below Bighorn FAS, the river enters motorized water. Jet boats are allowed on this lower section, which changes the character considerably. Fish numbers decrease as you move downstream, and water quality gradually shifts as the river picks up agricultural input. Most fly anglers focus on the upper 13 miles, but this stretch can produce solid fishing with less pressure if you don't mind the occasional motor passing through.

Flow Guide

Dam releases from the Afterbay control everything on this river. The Bureau of Reclamation manages releases to balance irrigation demands, recreation on Bighorn Lake, and downstream fishery health. Montana FWP has advocated for base flows of 2,500-3,500 CFS with periodic flushing flows of 6,000-8,000 CFS to clean spawning gravel and maintain channel health.

CFS Range	Conditions	Best For
Below 2,000	Low flows; excellent wading; side channels shallow	Walk-and-wade anglers; sight fishing to cruising trout
2,000-3,500	Ideal range; fish spread to flats and riffles	Dry fly fishing; float trips; best all-around conditions
3,500-5,000	Higher water; stronger current; good depth	Nymphing; streamer fishing from drift boats
Above 5,000	High water; limited wading; fast current	Experienced rowers only; flushing flows that benefit long-term habitat

Track current Bighorn River flows on RiverReports before making the drive. The ideal window for most anglers is 2,500-3,500 CFS, which provides enough depth to hold fish in their feeding lanes while keeping wading feasible in the upper section.

Hatches and Fly Patterns

The Bighorn's hatch calendar rivals any tailwater in the country. Stable flows and rich nutrient loads produce dense, predictable insect emergences from spring through fall. Hatch information sourced from Montana Angler, Bighorn Fly & Tackle, and local guide reports.

March-April: Midges and Early BWOs

Most Montana rivers are unfishable in March. The Bighorn is not. While the Madison and Yellowstone are running brown with snowmelt, the tailwater below the dam stays clear and in the upper 30s. It's cold, no question, but the fish are eating.

Early spring is a nympher's game. The workhorse rig is a Ray Charles Sow Bug (#14-16) with a Zebra Midge (#18-22) dropper, fished deep and slow through the softer runs. By late March, Blue-Winged Olives start showing on overcast days. BWOs on the Bighorn run larger in spring than on most tailwaters (sizes 14-16), and on a drizzly afternoon, you can find risers scattered across every flat. Carry RS2s (#16-20), Griffith's Gnats (#18-22), and BWO Parachutes (#14-18) to cover the hatch. Don't forget a Pink Scud (#14-16) for the subsurface work.

May-June: PMDs and Caddis

The PMD hatch in late June is when the Bighorn earns its reputation as a dry fly river. Pale Morning Duns start trickling off around mid-June and build through July, hatching in the slower flats and eddies where trout line up in feeding lanes. On a good day, you'll see dozens of fish rising in a single run, each one locked onto a specific drift line. It's the kind of fishing that rewards accuracy over distance.

Most PMDs run sizes 14-18, with 16 being the money size. The catch: trout often ignore the healthy duns sitting on top and focus on cripples and emergers stuck in the surface film. A Split Case PMD (#16-18) or PMD Comparadun (#14-18) fished in the film will outperform a standard dry most days. Carry Elk Hair Caddis (#14-16), Rusty Spinners (#16), and Pheasant Tail Nymphs (#14-18) for the overlap with early caddis activity.

July-August: Tricos, Caddis, and Terrestrials

A typical July day on the Bighorn has three acts. Act one: you're on the water at dawn for the Trico spinner fall. Tiny mayflies (#18-22) mate, drop to the surface, and die in clouds so thick they look like fog. Every trout in the river rises. It's technical fishing (12-14 foot leaders, 5X-6X tippet, downstream presentations to individual fish), and it's addictive. CDC Tricos (#20) and Trico Spinners (#18-22) are your weapons.

Act two starts mid-morning when the Trico fall ends. Switch to terrestrials. A Chubby Chernobyl (#10-12) or Parachute Ant (#14-18) tight to the banks produces aggressive strikes from fish that just spent two hours sipping tiny bugs.

Act three is the evening caddis. Tan caddis (#16-18) come off as the light fades, and a Poodle Sniffer or Elk Hair Caddis skated through the riffles can make a long day even longer in the best way.

September-October: Fall BWOs and Streamer Season

Fall BWOs fish differently than spring BWOs. The bugs are smaller (sizes 18-22 versus the spring's 14-16), and the trout are pickier after a summer of heavy hatch activity. You need finer tippets and better drifts. But the tradeoff is that you're sharing the river with far fewer anglers, and the fish you hook tend to be bigger. BWO Parachutes (#18-22), Black Caddis (#18-20), and Zebra Midges (#20-22) cover the surface and subsurface game.

The real fall opportunity is streamers. Brown trout turn aggressive ahead of their November spawn, and cloudy days with rising water can trigger some of the best streamer fishing of the year. Olive and black Woolly Buggers (#4-8) and articulated patterns (#2-6) stripped through the deeper runs produce the kind of violent strikes that keep you casting through cold afternoons. If you've been meaning to make your first trip, fall is the move.

November-February: Winter Nymphing

Winter fishing is subsurface work. Midges hatch daily, and sow bugs and scuds remain the staple diet. Water temps sit in the upper 30s, so fish move slowly but eat steadily in the deeper runs.

Key flies:

• Zebra Midge #18-22
• San Juan Worm #10-12
• Ray Charles Sow Bug #14-16
• Pink Scud #14-16
• Midge Cluster #18-20

Tip: Best window is 11am-3pm when water temps peak. Fish deep, fish slow, and target the softer runs where trout conserve energy.

Access and Logistics

Getting There

Fort Smith, Montana is the gateway to the Bighorn River, and it's remote. Plan accordingly.

• From Billings: ~60 miles south via Highway 313 (about 1.5 hours)
• Nearest commercial airport: Billings Logan International (BIL)
• From Bozeman: ~250 miles east (4+ hours)
• From Sheridan, WY: ~100 miles north (2 hours)

Fort Smith has a population around 100 people. There are no grocery stores, no gas stations with reliable hours, and limited cell service. Stock up in Billings or Hardin before making the final drive.

Float vs. Wade Fishing

Floating is the standard way to fish the Bighorn. Drift boats cover the most water and access fish that wade anglers can't reach. The 3-mile Afterbay to Three Mile float takes 3-4 hours of fishing. The full 13-mile float to Bighorn FAS is a long day.

Float	Distance	Approximate Time
Afterbay to Three Mile	3 miles	3-4 hours fishing
Three Mile to Bighorn FAS	10 miles	Full day (7-8 hours)
Afterbay to Bighorn FAS	13 miles	Very long day
Bighorn FAS to Mallards Landing	13+ miles	Full day (motorized water)

Wading is productive but limited. The first three miles below the Afterbay Dam offer the best wade access, with fine gravel bottom and gradual depth changes. Beyond Three Mile, shoreline access is extremely limited because the river flows through the Crow Indian Reservation. You can wade from the three FAS sites (Afterbay, Three Mile, Bighorn), but you cannot walk across reservation land to access the river at unauthorized points.

Wading safety: Felt-soled boots or studded rubber soles are essential. The Bighorn's bottom can be slick with algae, and sections that look shin-deep can be over ten feet. Use a wading staff and stay conservative.

Fly Shops and Outfitters

Fort Smith exists because of this fishery. Several quality operations serve visiting anglers:

• Bighorn Angler (Fort Smith): Full-service fly shop, guided trips, lodging, and vacation packages. Over 30 years on the river.
• Forrester's Bighorn River Resort (Fort Smith): Orvis-endorsed guides, resort lodging, and all-inclusive fishing packages.
• Bighorn Fly & Tackle (Fort Smith): Fly shop, lodging, drift boat rentals, and guided trips less than a mile from the river.
• Bighorn Trout Shop (Fort Smith): Guided trips, lodge accommodations, and full-service fly shop.

Guided float trips typically run $550-700 per day for 1-2 anglers, including rods, flies, and lunch. Book by March for peak summer dates (July-August). The Fort Smith shops are also your best source for current conditions. Call ahead the week before your trip. The folks at these shops fish the river every day and will tell you exactly what's working.

Crow Reservation and Regulations

The Bighorn River flows through the Crow Indian Reservation. A few important things to know:

Fishing license: A valid Montana fishing license is all you need to fish the Bighorn River itself. No tribal permit is required for fishing within the high-water marks.

Land access: Setting foot on reservation land above the high-water mark without a tribal recreation permit is not allowed. This means you can wade and float the river freely, but you cannot walk across reservation land to access the river at unauthorized points. Stick to the designated public access sites (Afterbay, Three Mile, Bighorn FAS). Trespassing on Crow Tribal land results in citations and fines.

Montana regulations on the river:

• Artificial lures only (cable to Bighorn FAS)
• Combined trout limit: 3 daily, only 1 over 18 inches
• Catch and release is strongly encouraged by local outfitters and conservation groups
• Open year-round
• Montana Conservation License + AIS Prevention Pass + Base Fishing License required

Nonresident license costs (2026): Season license $117.50; 5-day license $73.50. Purchase through the Montana FWP licensing system before arriving in Fort Smith.

Tips for First-Time Visitors

1. Stock up before Fort Smith. Billings or Hardin are your last stops for groceries, gas, and supplies. Fort Smith has limited services.
2. Book a guide for day one. Even experienced anglers benefit from a guided float to learn the river layout, access points, and current hatch activity.
3. Bring a range of leader sizes. Trico and BWO fishing demands 5X-6X, while streamer and nymph work calls for 3X-4X. The Bighorn rewards preparation.
4. Check flows before you go. Monitor conditions on RiverReports. The 2,500-3,500 CFS range is the sweet spot for most techniques.
5. Plan for weather. Southern Montana can swing from 90 degrees in July to unexpected cold fronts any month. Wind is common. Layer up and bring rain gear.
6. Respect the reservation. Stay within the high-water marks and use designated access points only. The Crow Nation has been generous in allowing public fishing access on the river.

Using RiverReports

Track real-time Bighorn River flows on RiverReports. The key gauge to watch is the Bighorn River below Yellowtail Afterbay Dam near St. Xavier, which shows dam releases that control conditions across the entire tailwater.

Compare current readings against the flow guide above to assess conditions before your trip. Flows between 2,500 and 3,500 CFS generally produce the best all-around fishing, while lower flows favor wading and sight fishing, and higher flows push fish to predictable holding lies for nymph and streamer anglers.

For anglers comparing Montana's best tailwaters, see our guide to the Missouri River for how the Bighorn stacks up.