Boulder River
Fly fishing in Montana · Intermediate · Best seasons: Summer, Fall
Target Species
Rainbow Trout, Brown Trout
About This Water
Near Big Timber with excellent freestone fishing. Wild rainbow and brown trout in beautiful canyon.
Fishing Recommendations
Welcome to one of Montana’s true "Blue Ribbon" gems. As your guide, I can tell you that the Boulder River is often overshadowed by its famous neighbors, the Yellowstone and the Madison. However, for the angler who loves fast-moving water, stunning scenery, and wild, aggressive trout, the Boulder is second to none.
Here is your comprehensive guide to fly fishing the Boulder River.
🎣 Location Overview
The Boulder River is a classic freestone river that begins in the Absaroka-Beartooth Wilderness and flows north to meet the Yellowstone River at Big Timber.
What makes it special is its dual personality. The Upper Boulder (above Natural Bridge Falls) is high-alpine, tumbling through boulder gardens and tight canyons. The Lower Boulder (below the falls) transforms into a broader, valley-bottom river flanked by cottonwoods and hay fields. It is remarkably scenic, with the jagged peaks of the Beartooths as your backdrop. Because it is un-dammed, it is a "flashy" river—meaning it reacts quickly to snowmelt and rain—but once it settles after runoff, it offers some of the best dry-fly fishing in the state.
🐟 Target Species & Behavior
The Boulder is home to hard-fighting, wild trout.
- Rainbow Trout: These are the primary residents of the faster water. They hold in the "pockets"—small eddies behind large rocks, the soft edges of heavy foam lines, and the heads of riffles. They are opportunistic and will often move several feet to smash a dry fly.
- Brown Trout: While found throughout the river, the larger Browns tend to congregate in the lower reaches where the water deepens. They hold under undercut banks, near submerged logs, and in the deep tailouts of pools. During the fall, they become highly aggressive as they prepare to spawn.
- Mountain Whitefish: You will find plenty of these in the deeper runs. They are great fighters and a sign of a healthy river ecosystem.
📅 Best Times to Fish
The Boulder is a seasonal river; timing your trip is critical.
- Summer (Late June – August): This is the prime window. Once the spring runoff subsides (usually late June or early July), the river becomes a dry-fly paradise.
- July: Peak "Hopper-Dropper" season.
- Time of day: 9:00 AM to 4:00 PM is usually the sweet spot for insect activity.
- Fall (September – October): This is my favorite time. The crowds vanish, and the Brown trout become active.
- September: Great terrestrial fishing and the start of the Blue Winged Olive (BWO) hatches.
- October: Streamer season. Focus on the lower river for big Browns.
- Conditions: Look for overcast days in October for the best BWO hatches and streamer action.
🪰 Recommended Flies & Techniques
Top Fly Patterns
- Dry Flies:
- Attractors: Royal Wulff (size 12-16), Chubby Chernobyl (Gold, Olive, or Tan, size 8-12), Purple Haze.
- Terrestrials: Morrish Hopper (Pink or Tan), Dave’s Hopper, Ants and Beetles.
- Match the Hatch: Parachute Adams, Sparkle Dun (PMD or BWO).
- Nymphs:
- Pat’s Rubber Leg (Brown/Orange), Prince Nymph (size 12-16), Pheasant Tail (size 14-18), and Lightning Bugs (Silver or Gold).
- Streamers:
- Woolly Bugger (Olive or Black), White Zonkers, or the Gallup’s Dungeon for the lower river.
Techniques
- High-Stick Nymphing: Because the river is so rocky, a short-line nymphing technique is lethal. Keep as much fly line off the water as possible to avoid the conflicting currents.
- Hopper-Dropper: This is the "standard" Boulder setup. Fish a large, buoyant dry fly (like a Chubby) with a 2-3 foot dropper to a weighted nymph.
- Pound the Banks: When floating or wading the lower river, get your flies within inches of the grass lines and undercut banks.
💡 Pro Tips & Local Knowledge
- The "Pocket Water" Secret: Don't spend too much time in the long, flat pools. On the Boulder, 80% of the fish are in the "pockets." If a spot looks like it's too small to hold a fish, cast there anyway.
- Wading Safety: The Boulder is notoriously slippery. The rocks are round and often covered in a fine layer of silt. Felt-soled boots and a wading staff are highly recommended.
- Floating vs. Wading: The Boulder is a difficult river to row. It is shallow and rocky. Only experienced oarsmen should attempt to float it, and only in a raft (hard-sided drift boats are risky here). For most anglers, walk-wade access provides the best experience.
- The Natural Bridge: Below the Natural Bridge Falls, the river actually disappears underground during low water years and re-emerges further downstream. Pay attention to water levels in late August.
⚠️ Important Information
- Access: Montana’s Stream Access Law is generous, allowing you to fish anywhere below the high-water mark. However, the Boulder flows through a lot of private ranch land. Use established Fishing Access Sites (FAS) like Green Mountain, any of the Bridge accesses, or the Main Boulder Station.
- Regulations: Always check the current Montana FWP Fishing Regulations. Usually, the Boulder is open year-round, but specific sections may have catch-and-release or tackle restrictions.
- Bear Safety: You are in Grizzly Country, especially on the Upper Boulder. Always carry bear spray and know how to use it.
- Permits: A valid Montana Fishing License and Conservation License are required for all anglers.
The Boulder is a physical river that rewards the active angler. Keep moving, keep your flies dry, and enjoy some of the purest trout water the West has to offer. Tight lines!
Bug Hatches & Matching Flies
| Hatch | Type | Peak months | Time of day | Hook sizes | Matching flies |
|---|---|---|---|---|---|
| Salmonfly Pteronarcys californica | stonefly | June, July | All day | #4-8 | Rogue River Stone #4-6, Pat's Rubber Leg #6-8, Cat Puke #4-8 |
| Golden Stonefly Hesperoperla pacifica | stonefly | June, July | Morning/Evening | #8-12 | Chubby Chernobyl (Gold) #8-12, Golden Twenty-Incher #10-12, Water Walker #10 |
| Pale Morning Dun (PMD) Ephemerella excrucians | mayfly | July, August | Late Morning/Afternoon | #14-18 | Sparkle Dun #16-18, Pheasant Tail #14-18, RS2 (PMD Color) #16-18 |
| Mother's Day Caddis Brachycentrus occidentalis | caddis | May | Afternoon | #14-16 | Peacock Elk Hair Caddis #14-16, LaFontaine's Deep Sparkle Pupa #14-16, Iris Caddis #14-16 |
| Blue-Winged Olive (BWO) Baetis | mayfly | April, May, September, October | Mid-day | #18-22 | Parachute Adams #18-22, Baetis Barr Emerger #18-20, Micro Mayfly #18-22 |
| Spruce Moth Choristoneura occidentalis | terrestrial | August | Morning/Afternoon | #12-14 | Spruce Moth (Tan) #12-14, Stimulator #12-14, Godard Caddis #12 |
| Yellow Sally Isoperla | stonefly | July | Afternoon/Evening | #14-16 | Little Yellow Sloan #14-16, Iron Lotus #16, Yellow Sally Foam Stone #14 |
| Grasshopper Orthoptera | terrestrial | August, September | Late Morning/Afternoon | #8-12 | Morrish Hopper #8-12, Parachute Hopper #10-12, Rainy's Grand Hopper #8-10 |