This Boulder River fishing report is valid from July 26 through August, 2025.
The Boulder is very low and will be too warm to fish well or ethically in its lower reaches after about 2:00PM. Up above Natural Bridge Falls, the afternoons will be fine except perhaps on the hottest days.
The Boulder is now functionally a large small stream. Fly choice should not be particularly complicated, but you need to get away from easy access points and areas that others have fished. This can be hard on the Boulder; walk a bit from the pullouts. Fish dry-dropper combos in general. If no rises, deep-nymph the heads of the larger pools.
- Hatches: Tan caddis, Yellow Sally, PMD, Nocturnal Stoneflies.
- Dry Flies: Small Chubby Chernobyls, hoppers, attractor dries like Trudes, Wulffs, Hazy Cripples, etc.
- Nymphs & Wets: Mostly smaller attractors with some flash, such as Copper Johns, Princes, Lightning Bugs, etc. If these don’t work, try more delicate tungsten-headed mayflies like PT Spankers and Perdigons. If dredging, pair your small nymph with a midsize stonefly.
- Streamers: Limited utility right now. Maybe some small olive Woolly Buggers fished under indicators or big ones dragged through the most turbulent rips. Otherwise, stick to nymph/streamer crossovers like TJ Hookers and Zirdles.
Boulder River Streamflow Data
This stream gauge is near Big Timber, right at the bottom of the Boulder near its confluence with the Yellowstone. The Boulder actually runs slightly higher near the Boulder Forks Fishing Access, since a great deal of water is pulled off for irrigation downstream. Further upstream, the Boulder is much smaller, since the East and West Boulder both come in near Boulder Forks.
Flows under 500cfs are fishable on foot, 500-1500 both on foot and floating, and 1500 to 2500 only floating.
