South Fork

Fly Fishing Report

SOUTH FORK

Report
OCT 28 — NOV 4, 2026
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Flow
1450CFS
SNAKE RIVER NR IRWIN ID
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Water Temp
48.9°F
Updated 2026-10-27
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Weather
30–54°F
Chance Light Rain then Mostly Cloudy
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Reported By
Bruce Staples
On the water
The South Fork is running clear and cold at 48.9°F with flows of 1,450 cfs at Irwin, dropping steadily as Palisades Reservoir continues to draw down. Wading opportunities are expanding, and migrating brown trout are responding to streamers in low-light conditions.
From the ShopBruce Staples · October 28, 2026

Water coming out of Palisades Reservoir (about 10% full) remains clear, cold, and will continue to drop. Flow in the river has decreased enough to offer numerous wading locations such as side channels and gravel bars, and a few locations where wading across is possible. Floating from the dam down to Conant is recommended as the safest option because of reducing daylight hours and emerging structure increasing chances for hard-sided boat damage.

Terrestrial insects are reduced because of killing frosts. Mahogany duns are active during midday but are decreasing in numbers. BWOs are most active during overcast conditions from late AM to early PM. October caddis take over topwater fishing as evening approaches but are decreasing in hatch intensity, and midges can be active throughout the day.

During low light and stormy conditions, stripped streamer patterns interest migrating brown trout. Fish those patterns around overhead cover and deep water. Flow varies around 1,500 cfs at Irwin, about 2,000 cfs at Heise, and about 700 cfs at Lorenzo.

Hatch Chart
Insect Size Activity Prime Time
Mahogany Dun #14–16 Moderate and decreasing Midday
Blue-Winged Olive (BWO) #20–22 Moderate, best on overcast days Late morning to early afternoon
October Caddis #8–12 Decreasing in intensity Evening
Midge #20–24 Consistent All day
Best Time Window
  • LATE MORNING TO EARLY AFTERNOON: Target BWO and mahogany dun hatches with dry flies and emergers, especially under overcast skies
  • EVENING: Switch to October caddis dry patterns as topwater activity picks up before dark
  • LOW LIGHT & STORMY CONDITIONS (dawn, dusk, overcast): Strip streamer patterns around overhead cover and deep water for migrating brown trout
Guide's Tip
From the benchTonight's forecast calls for a chance of rain and temperatures dropping to 31°F — those stormy, low-light conditions are exactly what Madison says triggers migrating brown trout on stripped streamers. Wednesday and Thursday clear up with highs of 46–54°F, which should produce solid midday mahogany dun and BWO windows. No dedicated mahogany dun dry fly is currently in the catalog; if you have a Mahogany Comparadun or Sparkle Dun in #14–16, bring it for the midday rise.
Main Species
Yellowstone Cutthroat Trout
Brown Trout
Rainbow Trout
Report generated October 28, 2026 — Next update: November 4, 2026