Idaho ·
South Fork Snake River Fly Fishing Report - August 16, 2026
SOUTH FORK SNAKE RIVER
ReportAUG 16 — 23, 2026
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Flow
12900CFS
SNAKE RIVER NR HEISE ID
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Water Temp
—
Updated 2026-08-15
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Weather
53–84°F
Mostly Clear
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Clarity
Clear
Check post-storm
The South Fork is pushing a robust 12,900 cfs at the Heise gauge (height 5.93 ft), creating fast, pushy water that is concentrating fish tight to the banks and in softer seams — clarity is good, so precise presentations matter. Sunny skies and a high of 83°F today will fire up terrestrial activity by mid-morning and keep it rolling through late afternoon.
What's Working — Hot Flies
Bionic Hopper - Tan #12
#12
Bionic Hopper - Purple #12
#12
Keller's Henneberry Hopper - Tan #12
#12
Coffey's CH Sparkle Minnow Sculpin #6
#6
Tungsten Pat's Rubber Legs - Tan & Brown #6
#6
Joe's Mini Crayfish Jig #6
#6
Bionic Ant 2.0 - Black #16
#16
Corn-fed Caddis (CDC) Tan #20
#20
Tungsten Split Case Nymph - PMD #20
#20
Egan's Thread Frenchie Jig - Olive #12
#12
Parachute - Blue Wing Olive #22
#22
Olsen's Straggle Stone Brown Barbless #12
#12
Hatch Chart
| Insect | Size | Activity | Prime Time |
|---|---|---|---|
| Grasshoppers / Terrestrials | #8-12 | Heavy | 10 AM - 5 PM |
| Mutant Stoneflies (Salmonfly/Golden Stone late stragglers) | #6-8 | Moderate | 8 AM - 11 AM |
| Caddis | #16-20 | Moderate | 6 PM - 8 PM |
| PMD (Pale Morning Dun) | #16-20 | Light | 9 AM - 12 PM |
| Blue-Winged Olive (Baetis) | #20-22 | Light | 5 PM - 7 PM |
Best Time Window
- 6:30 AM - 9:30 AM: Pre-wind nymphing in bank seams and inside bends with stonefly and Frenchie patterns before boat traffic builds.
- 10 AM - 4 PM: Prime hopper window — sunny skies and warming banks push fish into the top foot of water along grassy edges.
- 6 PM - 8 PM: Evening caddis and BWO activity in slower tailouts; switch to small dries and work the foam lines in fading light.
Guide's Tip
From the benchWith the river at 12,900 cfs, your boat position is everything — hug the banks and target the 2-4 foot strip of slower water between the main current and the grass. On the hopper, make a positive bank-slap cast and immediately feed slack so the fly drifts naturally before the current grabs your line. For nymphing, focus on the inside bends and back-eddies where the current drops off sharply; use enough split shot to get your fly to the bottom within the first few feet of the drift. Start early before the wind picks up around midday, and save your best hopper water for the 11 AM to 4 PM window when the sun has the banks warm and the fish are looking up.
Main Species
Yellowstone Cutthroat Trout
Brown Trout
Rainbow Trout
