Freestone · Mixed · Montana, US

Jefferson River

A broad, calm stretch of the Jefferson River bordered by grassy banks and cottonwood trees, with mountains in the distance.

The Jefferson is born where the Beaverhead, Ruby, and Big Hole all come together, and it grows into a big, slow, brushy valley river that hides some genuinely large brown trout under its banks.

Tomorrow · A proper day on the water
Pheasant Tail
Forecast · Tomorrow
A proper day on the water
A proper day for it. Work the seams with an upstream nymph, switch to the dry when they show.
65% projected
Today's fly
Pheasant Tail
Pheasant Tail
Conditions on the water · Tomorrow
Live gauge
Level
Rising
0.82 m
Lifting fast
Water temp12.4°C
ClarityVery coloured
Weather16°C
WindN 18 km/h
Pressure1010 hPa
Rain · recent0.0 mm
Rain · ahead0.0 mm

The nearest gauge doesn't record temperatures, so we've estimated it — defer to the river keeper's advice.

Water temperature for Rainbow Trout
Ideal
12°C est.ideal 10–18°C
0°14°28°
How to fish it · for Rainbow 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
Water at 20.2°C — above the brown trout caution line (18°C). Fish dawn or dusk only. Land it fast, wet hands, no air shots.
Likely species
Mayflies
Caddisflies
terrestrials
Hatch timeline · tomorrowPeak at 12pm

12pm(now) — Mahogany Dun

Stage: On emergersApproach: Emerger or dryActivity: 69%
Also:Reed Smut30%
Peak emergence window5 food groups active

Peak activity at 12pm — Mahogany Dun (Mahogany Dun, Peak emergence window)

Sub-surface · on the nymphunder the surface

Hatch predictions

See the full sub-surface read with Pro.

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Evidence
Records-basedModerate confidence

Based on species-occurrence records, not local invertebrate surveys.

Through the year
0–3 scale · September 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
Brown DunHatch
2
3
3
3
3
3
3
2
Western Green DrakeHatch
2
2
Flav (Small Western Green Drake)Hatch
2
3
2
Mahogany DunHatch
2
2

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

Ranked for today
Rainbow Trout fly box
SD
Sex Dungeon
2-6 · Pattern
Proven pattern for this period
Permits & access
Permit required — see local rules.
  • Montana licence
  • The Jefferson is one of the first rivers to go under summer hoot-owl restrictions — check FWP before an afternoon session.
What's coming
Plan ahead
5-day outlook
Cooler water nearby · 5
Water here at 20.2°C — the fishing's alive, but these are cooler if you'd rather rest the warm water.
Big Hole River
28 km
~11°C
Brown trout · Rainbow trout · Brook trout
Ruby River
33 km
~12°C
Brown trout
Beaverhead River
47 km
~12°C
Brown trout · Rainbow trout
Madison River
55 km
~12°C
Brown trout · Rainbow trout
Ennis Lake
52 km
~12°C
Brown trout · Rainbow trout
Gallery · 2
  1. A broad, calm stretch of the Jefferson River bordered by grassy banks and cottonwood trees, with mountains in the distance.
    Jefferson River at Silver Star, Montana
  2. Terrain map of the venue
    Terrain map
About this water

The Jefferson is born where the Beaverhead, Ruby, and Big Hole all come together, and it grows into a big, slow, brushy valley river that hides some genuinely large brown trout under its banks. It's a spring-and-fall proposition. Come summer it draws down, warms up, and goes under hoot-owl restrictions as quick as anything in the region — so fish the cool mornings and the shoulders of the year, and leave the hot afternoons to somebody who hasn't read the gauge.

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

EPA ATTAINS assessment unit 'Jefferson River' (MT41G001_011), 2021 Integrated Report. Aquatic Life use: Not Supporting. Listed impairment causes: Temperature, Sediment, Habitat Alterations, Hydrologic Alteration, 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) · MT41G001_011

The full read · show the working · for Rainbow Trout · confidence 80%
How the 26 is built — score × weight = contribution
Temperature25 × 28%7.0
Flow80 × 22%17.6
Clarity85 × 18%15.3
Feeding Time40 × 13%5.2
Pressure75 × 7%5.3
Insect activity33 × 12%4.0
Conditions total= 54
Can you trust it?
Water temperaturelive gauge readinggauge
Level / flowon-river gaugeobserved
Prey activitymodelled from regional profilemodelled
What would change the calculation
Cooler water — back toward the 10–18 °C ideal band — would lift the score and ease welfare.
The dawn and dusk windows score higher than the midday lull.
Directions
Apple MapsGoogle Maps
Seasons & zones
  • Trout Third Saturday of May → Last day of February
Related guides
Euro Nymphingsubsurface methods
Booking & contacts