Free Resource · Updated 2026
The South Fork of the Snake River below Palisades Dam runs through a canyon of cottonwoods and basalt cliffs. It holds native cutthroat and wild rainbow trout throughout its 65-mile run. The river is best known for its Green Drake and PMD hatches in summer and for consistent dry fly action on hoppers in late summer.
South Fork Snake River Hatch Calendar — Quick Reference
The South Fork drains out of Palisades Reservoir and runs west through Swan Valley before turning north toward Idaho Falls. The canyon section through the Box Canyon and the Cottonwood Reach are the most popular fishing areas. Boat fishing is common on the South Fork as the banks are brushy and wade fishing can be limited.
The river holds a healthy population of Snake River fine-spotted cutthroat and wild rainbows. Both species rise freely to dry flies during good hatches. The fish average 12 to 16 inches with larger specimens in the heavier water and back channels.
Green Drake hatches fire in late June and can produce all-day dry fly fishing. PMDs arrive in early July and continue through August. Caddis are active in May and June in the riffles. Hopper fishing picks up in late July and continues through September. PMD spinner falls in the evenings are particularly productive.
See the full Idaho Fly Hatch Chart for hatch timing across all of Idaho's top trout streams.
Check Conditions Near South Fork Snake RiverWhat to Fish
Green Drake hatches on the South Fork light up the river in late June. The big duns come off through the mid-morning and afternoon and cutthroat rise aggressively. Fish the riffles and runs with a size 12 Parachute Green Drake or Harrop Dun. This is the most exciting dry fly period of the year on the South Fork.
Recommended: #10-12 Parachute Green Drake
Hopper fishing on the South Fork reaches its peak in August. Grasshoppers blow into the river from the canyon banks and cutthroat slash at the surface. Fish a big foam hopper near the banks with a small nymph dropper. The dropper often outfishes the dry but the dry fly strikes are the most satisfying.
Recommended: #6-10 Dave's Hopper, Chernobyl Ant
Caddis are active in the riffled sections of the South Fork from May through July. The heaviest caddis activity is in June on the faster reaches. Fish an Elk Hair Caddis dead-drift through the riffles or skitter it slightly to trigger a response from fish looking for egg-laying caddis.
Recommended: #14-18 Elk Hair Caddis, X-Caddis
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