Montana ·
Bighorn River Fly Fishing Report - September 6, 2026
BIGHORN RIVER
ReportSEP 6 — 13, 2026
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Flow
1500CFS
Bighorn R bl Yellowtail Afterbay Dam nr St. Xavier
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Water Temp
—
Updated 2026-09-05
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Weather
55–86°F
Mostly Clear
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Clarity
Clear
Check post-storm
Flow is running 1,500 CFS out of Yellowtail Afterbay Dam with gauge height at 59.89 ft — slightly lower than last week and in excellent shape with clear water. Expect a warm, sunny Sunday topping out near 86°F before storm chances move in Sunday night, so plan your day accordingly.
What's Working — Hot Flies
Juju Baetis Tungsten #22
22
Olsen's Peacock Blowtorch Barbless #22 - 24
22-24
Black Zebra Midge(TBH) #20
20
Parachute - Blue Wing Olive #22
22
Top Secret Baetis #16
16
Tungsten Split Case Nymph - PMD #20
20
Egan's Thread Frenchie Jig - Olive #12
12
Corn-fed Caddis (CDC) Tan #20
20
Bionic Ant 2.0 - Black #16
16
Egan's Frenchie #12
12
Roza's World Spain Perdigon Barbless #18 - 32
18
Coffey's CH Sparkle Minnow Sculpin #6
6
Hatch Chart
| Insect | Size | Activity | Prime Time |
|---|---|---|---|
| Baetis (Blue-Winged Olive) | 20-22 | Moderate | 10 AM - 2 PM |
| Caddis | 16-18 | Moderate | 4 PM - 7 PM |
| PMD (Pale Morning Dun) | 18-20 | Light | 9 AM - 12 PM |
| Midge | 20-24 | Heavy | 7 AM - 10 AM |
| Terrestrials (Ants) | 14-16 | Moderate | 11 AM - 4 PM |
Best Time Window
- 6:30 AM - 10 AM: Early midge hatch in the tailouts — nymph the flats with small zebra midges and blowtorches before the sun gets high.
- 10 AM - 2 PM: Prime BWO window — watch for rising fish in the softer water and be ready to switch to a dry fly when you see sipping activity.
- 5 PM - 7:30 PM: Evening caddis and terrestrial action heats up along the banks — skitter a CDC caddis through the riffles and drift ants tight to the grass before dark.
Guide's Tip
From the benchWith 1,500 CFS and clear water, the Bighorn's fish have seen pressure and are leader-shy — drop to a 5X or 6X tippet for your midge and baetis presentations and keep your leader at least 9 feet. Focus your morning on the flat, glassy tailouts below the riffles where midges concentrate, then shift to the main current seams as the BWO hatch develops mid-morning. The afternoon heat will push fish into shaded banks and deeper slots, so work terrestrials and attractor nymphs tight to structure. Keep an eye on the sky Sunday evening — storm cells could move in after 10 PM, so plan to be off the water by dark.
Main Species
Brown Trout
Rainbow Trout
Mountain Whitefish
