South Fork

 

SOUTH FORK

Report
JUL 30 — AUG 6, 2026
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Flow
11800CFS
SNAKE RIVER NR IRWIN ID
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Water Temp
48.9°F
Updated 2026-07-30
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Weather
60–94°F
Sunny then Patchy Smoke
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Reported By
Bruce Staples
On the water
The South Fork is running clear and cool at 11,800 cfs (USGS at Irwin), with PMDs, yellow sallies, and caddis drawing trout to the surface in defined windows. Boating is the safest and most effective approach at current flows.
From the ShopMadison Losee · July 30, 2026

Flow out of Palisades Dam is around 13,000 cfs, 13,600 cfs at Heise, and 8,680 cfs at Lorenzo. Coming out of the dam, this clear, cool flow keeps water temperatures ideal for trout. Most trout are in slower waters such as near banks, eddies, around seams, and just behind structure.

PMDs and yellow sallies — with some damselflies on slow-moving channels — make up most of the insect activity that attracts trout toward top waters. The best time to encounter fish rising for them is between mid-morning and early afternoon. Mid-day sun tends to make trout seek out shade, depth, and other overhead cover. Ants and beetles are becoming numerous.

Wading is strictly limited to soft, shallow waters, so boating is the safest and most effective way to fish. Most popular launch sites, such as Conant and Byington, are becoming crowded especially on weekends. Bring your tolerance because not all users play by the rules.

Fish woolly bugger, San Juan worm, rubber leg, and streamer patterns and double nymph rigs deep throughout the river. Caddis activity is best during late afternoon and evening hours.

Hatch Chart
Insect Size Activity Prime Time
PMD (Pale Morning Dun) #16–#20 Moderate–Heavy Mid-morning to early afternoon
Yellow Sally (Little Yellow Stonefly) #14–#16 Moderate Mid-morning to early afternoon
Caddis #16–#20 Moderate Late afternoon and evening
Ants & Beetles (Terrestrials) #14–#18 Building Late morning through afternoon
Damselfly #12–#14 Light (slow channels) Mid-morning to early afternoon
Best Time Window
  • MID-MORNING TO EARLY AFTERNOON (9 AM–1 PM): Prime dry fly window for PMDs and yellow sallies — target rising fish along banks, eddies, and seams.
  • LATE AFTERNOON TO EVENING (4 PM–DARK): Caddis activity picks up; switch to caddis dries and swing soft hackles through runs.
  • ALL DAY: Fish rubber legs, San Juan worms, woolly buggers, and streamer patterns deep throughout the river from the boat — consistent action regardless of surface activity.
Guide's Tip
From the benchMadison specifically called out woolly bugger and San Juan worm patterns as producers — if you have a classic Woolly Bugger (olive or black) and a standard San Juan Worm in your box, bring them. For yellow sally dry fly action during the mid-morning window, a size #14–#16 yellow stimulator or elk hair caddis in yellow will cover you. Plan to be on the water and fishing dry flies by 9–10 a.m. to catch the PMD and yellow sally window before mid-day heat pushes fish down.
Main Species

Yellowstone Cutthroat Trout

Brown Trout

Rainbow Trout
Report generated July 30, 2026 — Next update: August 6, 2026