Bighorn River
Fort Smith · 13-Mile Reach
S Montana, USA
Open live forecast →Target species: Rainbow and Brown.
Stream gauge: 06287000. Flow and water temperature update on every refresh.
Weekly AI Outlook as of 06/05/26
The Bighorn sits at 1,490 cfs with crystal clear water — classic June conditions that reward precision over power. PMDs and caddis are driving the action, with midday emergence windows for PMDs when air temps climb into the 80s-90s early week. Technical fishing in gin-clear water means long leaders and drag-free drifts are non-negotiable. Evening caddis action should fire as temps cool through the weekend cold front.
- Flow: 1,490 cfs — stable and clear, perfect June level for wading access to technical lies
- Hatches: PMD emergence midday as air temps hit 88-96°F, evening caddis as temps drop. Midges steady all day
- Water Temp: Mid-50s — ideal for PMD activity and sustained trout feeding through afternoon heat
- Best Window: 11am-2pm for PMD emergence, 7-9pm for caddis as Saturday's cold front arrives
Generated weekly from live USGS gauge readings, weather forecasts, and recent fly shop reports. Updates Friday mornings.
About this Water
- Tailwater
- Best months: Year-round; best May–Oct. Peak: June (caddis/PMD) and Oct (browns/streamers)
The Bighorn River below Yellowtail Dam in Fort Smith, Montana is one of the most productive tailwater fisheries in North America — a 13-mile reach of cold, clear, nutrient-rich water supporting extraordinary densities of large rainbow and brown trout. The river is famous for its midge hatches, scud patterns, and the most technical dry fly fishing in the Rockies — size 24 to 28 flies to fish feeding in thin current seams. The Bighorn is not a wilderness experience but it is a numbers fishery of rare quality.
The Bighorn's fish-per-mile count in the prime section below Yellowtail Dam is among the highest measured for any river in the Rocky Mountain West — verified by Montana FWP electrofishing surveys showing 5,000+ trout per mile in peak years.
January Outlook
The Bighorn River below Yellowtail Dam near St. Xavier is one of Montana's — and Wyoming's — finest winter tailwaters. Year-round midge hatches in the dam-release section. Cold air but consistent fishing.
Productive Patterns
- Zebra Midge
- RS2
- WD-40
- Juju Baetis
Tips
The 13-mile quality water section from the dam to the Bighorn access stays productive year-round. January midging requires small patterns and patience. Access via the St. Xavier road.
Water Notes
Dam-regulated 2,500–6,000 cfs. Water 42–48°F year-round. Open despite air temps well below zero. One of the upper midwest's finest winter tailwaters.
February Outlook
February midging on the Bighorn tailwater. The dam-regulated water keeps conditions remarkably consistent through winter. Large rainbow and brown trout are active year-round in the quality water section.
Productive Patterns
- Zebra Midge
- RS2
- Mercury Midge
- Pheasant Tail
Tips
Fish the 13-mile quality section from Yellowtail Dam downstream. The first three miles below the dam are consistently productive in winter. 6X tippet and tiny patterns are the key.
Water Notes
2,500–5,500 cfs. Water 42–48°F. Constant tailwater. Open year-round below Yellowtail Dam.
March Outlook
The Bighorn tailwater below Yellowtail Dam is open year-round. Midge and Baetis action warms up in March with some of the river's most consistent dry fly fishing on productive grey winter days.
Productive Patterns
- Zebra Midge
- RS2
- Mercury Baetis
- WD-40
Tips
The 13-mile reach below Afterbay Dam is the prime section. Fish the long flat tailouts below riffles with double midge rigs on 6X. The Bighorn is cold — neoprene waders are recommended.
Water Notes
Regulated 1,200–2,500 cfs. Water 45–52°F. Clear and consistent from the dam release.
April Outlook
Spring on the Bighorn brings excellent Baetis and midge hatches. One of North America's finest tailwaters fishing at full capacity.
Productive Patterns
- Blue Winged Olive
- Parachute BWO
- RS2
- Flashback Pheasant Tail
Tips
April is among the Bighorn's finest months — consistent flows, rising fish, and minimal crowds. The Bighorn is famous for sight-fishing to large rainbows and browns in clear water. 5X–6X tippet.
Water Notes
1,200–2,200 cfs. Water 48–56°F. Protected from runoff — the dam regulates flow perfectly.
May Outlook
PMD and caddis hatches begin in May, layering onto the existing Baetis and midge activity. The Bighorn's dry fly season is in full swing.
Productive Patterns
- PMD Sparkle Dun
- Elk Hair Caddis
- Pale Morning Dun
- Soft Hackle Emerger
Tips
The Bighorn's famous sight-fishing is at its peak in May. Float the 13-mile reach to cover all the prime water. The downstream sections near Three Mile Access are wade-accessible.
Water Notes
1,200–2,500 cfs. Water 52–60°F. Outstanding spring tailwater conditions.
June Outlook
Excellent caddis and PMD action throughout June. The Bighorn's insect diversity is remarkable for a tailwater.
Productive Patterns
- Elk Hair Caddis
- PMD
- Trico Spinner
- Pale Morning Dun
Tips
The Bighorn's evening caddis hatch is exceptional. Fish the long runs and riffles below the Two Leggins section. Float trips from Afterbay Dam to Bighorn Access provide diverse fishing.
Water Notes
1,200–2,500 cfs. Water 56–64°F. Prime season.
July Outlook
Trico hatches become the signature event in July. The Bighorn's Trico spinner fall is among the best in North America — massive falls of size 22–24 flies bring even the largest trout to the surface.
Productive Patterns
- Trico Spinner
- Trico Dry
- Pale Evening Dun
- Elk Hair Caddis
Tips
The Trico spinner fall begins mid-morning and can last several hours. Fish need to be approached carefully during the fall. The pools below the riffles concentrate the most fish.
Water Notes
1,200–2,200 cfs. Water 60–66°F. Hot afternoons — fish mornings for Trico spinner fall.
August Outlook
Trico season continues through August with excellent early morning fishing. Afternoon terrestrial fishing with ants and beetles supplements the Trico activity.
Productive Patterns
- Trico Spinner
- Ant
- Beetle
- Pale Evening Dun
Tips
August Trico fishing on the Bighorn is a bucket-list experience. Get on the water by 7am. The afternoon heat slows activity — shift to streamers or take a break until evening.
Water Notes
1,000–2,000 cfs. Water 62–68°F. Hot afternoons. Fish early for Tricos.
September Outlook
Baetis return in September with excellent fall BWO fishing. Cooler temperatures make all-day fishing comfortable again.
Productive Patterns
- Blue Winged Olive
- Parachute BWO
- Elk Hair Caddis
- Streamer
Tips
Fall on the Bighorn is exceptional — Baetis hatches, brown trout beginning to color up, and far fewer guides and anglers than summer. The streamer fishing for large browns is outstanding.
Water Notes
1,000–2,000 cfs. Water 58–64°F. Excellent fall tailwater conditions.
October Outlook
October brings spawning brown trout and exceptional streamer fishing. The Bighorn's large brown trout are at their most aggressive.
Productive Patterns
- Streamer
- Woolly Bugger
- Articulated Streamer
- Sculpin Pattern
Tips
October is prime big-fish month on the Bighorn. Trophy brown trout move up from the reservoir and become aggressive. Streamers fished on sink-tip lines produce the most memorable fish.
Water Notes
1,000–1,800 cfs. Cooling 50–58°F. Outstanding fall trophy trout conditions.
November Outlook
November on the Bighorn is excellent. The fall BWO season extends into the tailwater quality section and midge fishing is consistent. Significantly less pressure than the summer peak season.
Productive Patterns
- Zebra Midge
- RS2
- Blue Winged Olive
- WD-40
Tips
November on the Bighorn is underappreciated — excellent fishing, few anglers. The Afterbay access points are open year-round. Winter fishing pressure is a fraction of the summer crowds.
Water Notes
2,500–5,500 cfs. Water 42–50°F. Stable tailwater. Good fall/winter access at Afterbay.
December Outlook
Year-round tailwater fishing below Yellowtail Dam. December midge fishing for large rainbow and brown trout. Cold Wyoming winter conditions but consistent fish activity.
Productive Patterns
- Zebra Midge #22-24
- RS2
- Mercury Midge
- WD-40
Tips
The Bighorn tailwater is open and fishable year-round. December fishing focuses on the deep slots near the dam. Bundle up — Wyoming winters are serious. The fish are worth it.
Water Notes
2,500–5,000 cfs. Water 40–46°F. Open year-round. Ice on banks but main channel open.
Hatch Calendar
| Insect | Peak | Active | Size | Productive Patterns |
|---|---|---|---|---|
| Midge Chironomidae |
Jan, Feb, Mar, Nov, Dec | Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec | #18–22 |
|
| Blue Winged Olive Baetis spp. |
Apr, Oct | Mar, Apr, May, Sep, Oct, Nov | #16–22 |
|
| Pale Morning Dun Ephemerella inermis |
Jul, Aug | Jun, Jul, Aug | #16–18 |
|
| Caddis (Black) Chimarra atterrima |
Jul | Jun, Jul, Aug | #16–22 |
|
| Caddis (Tan) Hydropsyche spp. |
Jul, Aug | Jun, Jul, Aug, Sep | #16–18 |
|
| Trico Tricorythodes spp. |
Aug | Jul, Aug, Sep, Oct | #20–24 |
|
| Sulphur Ephemerella excrucians |
Jul, Aug | Jul, Aug | #16–18 |
|
| Scud Gammarus / Hyalella |
Mar, Apr, May, Nov, Dec | Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec | #14–18 |
|
Access & Approach
Fort Smith, MT (fly to Billings then drive 60 miles south). Multiple guide services based in Fort Smith. Drift boat is the most efficient fishing method. Montana fishing license required. BLM manages access via boat ramps.
Nearby Fly Shops
- Bighorn Angler
- Bighorn Trout Shop
Regulations & License
Fishing in Montana requires a current license. Always verify season dates, bag limits, and any special-regulation waters before you fish.
Montana fishing regulations & license →
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About Current
Bighorn River conditions on Current combine real-time flow data (USGS, WSC, CDEC, CEHQ), weather, tide predictions, hatch probabilities calibrated to this specific water, and recent fly shop reports from the area.
Bighorn River is one of 245 hand-curated waters in Current. The app and web forecast also generate AI outlooks for any unlisted river, lake, or saltwater flat anywhere in the world — drop a pin or paste a name and Current produces a fresh seasonal outlook with weather, flow context, and recommended techniques.
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