Idaho ·
South Fork Snake River Fly Fishing Report - September 20, 2026

SOUTH FORK SNAKE RIVER
ReportSEP 20 — 27, 2026
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Flow
5320CFS
SNAKE RIVER NR HEISE ID
🌡️
Water Temp
—
Updated 2026-09-19
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Weather
44–74°F
Isolated Rain Showers
💧
Clarity
Clear
Check post-storm
Flow has dropped to 5,320 cfs at Heise (gauge height 3.46 ft), down noticeably from last week's 6,670 cfs — fish are concentrating along cut banks and in classic seam water, making them more predictable and easier to target. Water remains clear, and with a mostly sunny Sunday topping out at 67°F, expect a full terrestrial and afternoon mayfly window.
What's Working — Hot Flies

Bionic Hopper - Tan #12
#12

Bionic Hopper - Purple #12
#12

Bionic Ant 2.0 - Black #16
#16

Bionic Ant 2.0 - Brown #12
#12

Parachute - Blue Wing Olive #22
#22

Top Secret Baetis #16
#16

Egan's Thread Frenchie Jig - Olive #12
#12

Egan's Frenchie #12
#12

Corn-fed Caddis (CDC) Tan #20
#20

Coffey's CH Sparkle Minnow Sculpin #6
#6

Tungsten Jig Bugger - Olive - Barbless #14
#14

Juju Baetis Tungsten #22
#22
Hatch Chart
| Insect | Size | Activity | Prime Time |
|---|---|---|---|
| Grasshoppers / Terrestrials | 10-14 | Heavy | 11 AM - 4 PM |
| Ants | 14-18 | Moderate | 10 AM - 3 PM |
| Blue-Winged Olive (Baetis) | 18-22 | Moderate | 1 PM - 5 PM |
| Caddis | 16-20 | Light | 5 PM - 7 PM |
| Midges | 20-24 | Light | 8 AM - 10 AM |
Best Time Window
- 7 AM - 10 AM: Pre-sun nymphing with Frenchies and Jig Buggers along deep bank shelves before the hopper bite turns on.
- 11 AM - 4 PM: Prime terrestrial window — hoppers and ants along grassy cut banks with mostly sunny skies and light wind.
- 4 PM - 7 PM: BWO and caddis evening rise in the slower tailouts; switch to dry flies and emergers on a long, fine leader.
Guide's Tip
From the benchWith flows dropping to 5,320 cfs, fish have moved off the mid-river gravel bars and are stacking tight to the cut banks and willow-lined edges — position your boat within 10 feet of the bank and make short, accurate casts rather than long cross-current throws. During the midday hopper window, work the shaded bank on the east-facing bends first; the big browns are sitting in the shadows waiting for a meal to fall off the grass. If you see a fish rise and refuse your hopper, immediately downsize to a #16 Bionic Ant in the same lane — they're often looking at both and the ant will close the deal.
Main Species
Yellowstone Cutthroat Trout
Brown Trout
Rainbow Trout
