Fly Fishing Bighorn River - Below Yellowtail Afterbay

The Bighorn River below Yellowtail Afterbay is one of the most productive tailwater fisheries in the lower 48 states, offering world-class fly fishing for large, healthy trout in a stunning high-plains setting. This massive tailwater is renowned for its incredible trout densities, consistent flows, and trophy-sized fish that draw anglers from around the globe. The section flows through open ranchland and agricultural areas near Fort Smith, with the Bighorn Mountains providing a spectacular backdrop. The combination of excellent water quality, stable flows, and exceptional trout populations makes this one of the most sought-after tailwater fisheries in the American West.

The tailwater section below Yellowtail Afterbay is characterized by large, powerful flows that create diverse water types including fast riffles, deep runs, extensive gravel bars, and classic tailwater pools. The river bottom consists of cobble, gravel, and some sand, providing excellent habitat for both trout and aquatic insects. The gradient is moderate to gentle, creating excellent holding water throughout the section. The banks are lined with cottonwoods, willows, and agricultural fields, providing essential cover and shade. The water clarity is typically excellent, with stable temperatures year-round due to the tailwater releases from Yellowtail Afterbay. This is big water that demands respect, with flows typically ranging from 2000 to 4000 CFS year-round, though flows can peak around 7,872 CFS in June.

This section supports exceptional populations of wild brown trout and rainbow trout, with fish typically ranging from 14 to 18 inches. The brown trout are particularly large and healthy, often exceeding 20 inches and occasionally reaching 26+ inches. Rainbow trout are also well-represented and known for their acrobatic fights and vibrant colors. The tailwater's stable flows and excellent food base support some of the highest trout densities in Montana. Trophy fish exceeding 24 inches are common, with fish over 26 inches possible. The tailwater fishery was created by dam construction, which reduced spring flooding and increased fall/winter flows, establishing the blue ribbon fishery conditions present today. Mountain whitefish are also abundant and provide consistent action.

Hatch activity is exceptional throughout the year, with a variety of mayflies, caddis, midges, and scuds providing consistent fishing opportunities. The tailwater is famous for its prolific midge hatches year-round, with small patterns (#18-22) being particularly effective. Pale Morning Duns (PMDs) and various caddis species provide excellent dry fly opportunities during late spring and early summer. Blue-winged Olives emerge in spring and fall, providing additional dry fly opportunities. Scuds and sowbugs are extremely abundant and provide consistent subsurface action. Streamer fishing can be particularly productive, especially when targeting larger brown trout. Nymphing with tandem rigs is highly productive year-round, as trout continue feeding on nymphs even when not visibly rising.

Optimal wading flows for the tailwater section range from 2000 to 4000 CFS, with flows above 5000 CFS becoming challenging for safe wading. Flow management significantly affects wading, with the dam's operational changes creating a more regulated hydrograph with less variability compared to pre-dam conditions, resulting in more stable wading conditions year-round. The river is excellent for float fishing in drift boats and rafts, with numerous access points making it easy to plan multi-day floats or shorter day trips. Access is excellent along local roads, with numerous public access points, fishing access sites, and pullouts throughout the section. The town of Fort Smith provides limited services, with additional services available in Hardin and Billings. The nearest major commercial airport is Billings Logan International (BIL), approximately 90-120 minutes away.

The Bighorn River below Yellowtail Afterbay is a world-class tailwater fishery that offers some of the finest fly fishing in Montana. Its combination of exceptional trout populations, stable flows, and year-round fishing opportunities makes it a bucket-list destination for serious fly anglers. The section's reputation for trophy-sized trout and incredible insect biomass makes it one of the most productive and sought-after tailwater fisheries in the American West.