Fly Fishing Bighorn River - Thermopolis

Overview

The Bighorn near Thermopolis runs north from the mouth of Wind River Canyon through broad riffles, long glides and pools beside gravel bars. Releases from Boysen Reservoir influence the current, and brown, rainbow and cutthroat trout inhabit the reach. Scud, worm and midge patterns suit the subsurface water; rising fish in softer seams call for careful casts and drag-free drifts.

Tailwater Character

The Bighorn here is fed by bottom releases from Boysen Reservoir, and that single fact shapes everything about how it fishes. The dam captures sediment and buffers temperature, but tributary runoff and weather can still alter local clarity and temperature. Trout feed on a mix of midges, scuds, and aquatic worms supplemented by seasonal mayfly and caddis hatches. Brown trout and rainbow trout share the reach with Snake River cutthroat trout — Wyoming Game & Fish manages this stretch specifically as a trophy fishery for all three — and mountain whitefish are abundant throughout.

Reading the Water

Boysen Dam releases influence this river, while tributary inflow, diversions and local conditions can change the water downstream. Look at current and depth where you intend to fish, paying attention to seams beside faster channels and the drop into a pool.

Tactics on the Bighorn at Thermopolis blend classic tailwater nymphing with rewarding dry-fly windows. On most days, a two-fly nymph rig under an indicator is the bread and butter: a scud or worm pattern paired with a small midge or mayfly nymph, drifted through the riffles, runs, and along the seams of the deeper pools. A 9- to 10-foot 5-weight gives the reach to manage long drifts, and fluorocarbon tippet in the 4X to 6X range matches the clarity of the bottom-release water. When the Tricos or BWOs come off, switch to a single dry or a dry-dropper and hunt for pods of risers in the soft water — these fish key tightly on the naturals, so an accurate cast and a drag-free drift matter more than fly size.

Choose a lie you can reach with a controlled drift. A nymph can follow the deeper edge of a riffle, while a dry fly belongs in the feeding lane of a visible rise. Adjust the presentation as depth and current change.

Hatches on this tailwater follow a dependable calendar. Midges are present every month of the year and are the backbone of the winter and early-spring fishery, fished as size 20-24 pupae under an indicator or as tiny dries during midday cloud cover. Blue-Winged Olives are the signature mayfly, emerging in two waves — a spring window from roughly mid-spring into late spring and a fall window through fall — and overcast, drizzly days bring the best of it on size 18-22 imitations. Caddis fill the warm-season gap from late spring through early fall, Pale Morning Duns add midday surface action through the heart of summer, and Tricos bring technical morning spinner falls from mid-summer into fall. When the banks warm up, hoppers and ants pull fish to the surface along the grassy edges. Through it all, the subsurface game with scuds, midge larvae, and worm patterns produces fish on the days when nothing is showing on top.

Thermopolis makes a base for exploring the river and nearby canyon scenery. The headwater freestone of the Upper Wind River near Dubois offers a different part of the same basin.

Access

Wedding of the Waters Public Access Area, south of Thermopolis off US 20, has designated parking and a developed boat ramp on the Bighorn. Use the signed access road into the managed site.