Freestone · Mixed · Montana

Boulder River

Fast whitewater cascading through a boulder-strewn canyon on the upper Boulder River in Sweet Grass County, Montana, flanked by conifer forest

The Boulder is a pretty little freestone off the Absaroka–Beartooth front, the kind of river you'd happily fish even if it were empty — and it isn't.

Prime · Brown Trout
Parachute Adams · 12-18
Primelive now
About as good as it gets
River steady at a fishable height. On the feed top to bottom — start on the rises with a dry, drop a nymph if they stay down.
90% confidence
What moved it
  • Level0.67 mLast reading 17h ago
  • Water temp15.5°C
  • ClarityClear
Today's fly
Parachute Adams
Parachute Adams12-18
High-confidence seasonal pick
Conditions on the water
Live gauge
Level
Steady
0.67 m
Last reading 17h ago
Water temp15.5°C
ClarityClear
Weather16°C
WindS 7 km/h
Pressure1016 hPa
Rain · recent0.9 mm
Rain · ahead0.0 mm

Live readings — water temperature is an estimate where the gauge does not record it.

Water temperature for Brown Trout
Ideal
16°C est.ideal 10–16°C
0°14°28°
How to fish it · for Brown Trout
When
Nymphing can work through most of the day.
Where
Cover mixed depths.
Method
Start with tight-line nymphs and adjust if fish rise or drift higher.
Kit
9 ft #4 rod, floating line, 12 ft tapered leader to 4–5 lb fluoro tippet.
Why this works
Excellent — water temperature is right today, though insect activity could be better.
Hatch timeline · todayQuiet day

Hatch predictions

Today's headline hatch shown — see all 5 active hatches hour by hour with Pro.

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Sub-surface · on the nymphunder the surface

Hatch predictions

Top nymph shown — see all 2 guilds with Pro.

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Beyond the hatch · worth watchingambient prey

Hatch predictions

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Evidence
ModelledModerate confidence

Modelled from regional ecology — no survey or occurrence data for this water yet.

Through the year
0–3 scale · July highlighted
J
F
M
A
M
J
J
A
S
O
N
D
Trout seasonSeason
2
1
1
2
2
2
2
2
2
2
Western Green DrakeHatch
2
2
Flav (Small Western Green Drake)Hatch
2
3
2
Mahogany DunHatch
2
2
American March BrownHatch
2
3
2

Numbers are intensity 0 (none) to 3 (peak) — a guide, not a guarantee.

Ranked for today
Brown Trout fly box
Permits & access
Permit required — see local rules.
  • Montana licence
  • Yellowstone/westslope cutthroat are native here — handle and release them gently.
What's coming
Plan ahead
5-day outlook
Other water nearby · 5
Paradise Valley Spring Creeks
30 km
Rainbow trout · Brown trout
Shields River
46 km
Brown trout · Rainbow trout
Yellowstone River
50 km
Brown trout · Rainbow trout · Cutthroat trout
Stillwater River
60 km
Rainbow trout · Brown trout · Cutthroat trout
Gallatin River
88 km
Rainbow trout · Brown trout
Gallery · 2
  1. Fast whitewater cascading through a boulder-strewn canyon on the upper Boulder River in Sweet Grass County, Montana, flanked by conifer forest
    Whitewater on the upper Boulder River, Sweet Grass County, Montana
  2. Terrain map of the venue
    Terrain map
About this water

The Boulder is a pretty little freestone off the Absaroka–Beartooth front, the kind of river you'd happily fish even if it were empty — and it isn't. Rainbows, browns, brook trout, and cutthroat all live here. Once the snowmelt clears off in summer it's classic pocket-water dry-fly fishing, an attractor bouncing through the pockets and a fish meeting it more often than you'd guess.

  • Mixed
Water quality · US Clean Water Act
  • Aquatic life: Impaired
What this classification means

EPA ATTAINS assessment unit 'Boulder River' (MT43B004_132), 2021 Integrated Report. Aquatic Life use: Not Supporting. Listed impairment causes: Nutrients, Habitat Alterations, Metals Other Than Mercury. This is a Clean Water Act assessment-unit classification (the US analogue of WFD), not a live reading.

Status is for the Clean Water Act assessment unit covering this reach.

EPA ATTAINS (Clean Water Act) · MT43B004_132

The full read · show the working · for Brown Trout · confidence 90%
How the 84 is built — score × weight = contribution
Temperature100 × 28%28.0
Flow80 × 22%17.6
Clarity95 × 18%17.1
Feeding Time70 × 13%9.1
Pressure80 × 7%5.6
Insect activity52 × 12%6.2
Conditions total= 84
Can you trust it?
Water temperatureair-to-water estimateestimated
Level / flowon-river gaugeobserved
Prey activitymodelled from regional profilemodelled
Directions
Apple MapsGoogle Maps
Seasons & zones
  • TroutThird Saturday of May → Last day of February
Related guides
Euro Nymphingsubsurface methods
Booking & contacts