Snake River
Surface action on midges is occurring primarily from around noon until 4pm in deeper ledge rocks, eddies and riffle pools (especially those with moderate depths and slow currents). Tandem rigs – double emergers or adult/emerger combos – are working best.
Double nymphs can produce in deeper, faster pools but the best action on nymphs is coming on dry-droppers in riffles pools and eddies. Two to three feet of dropper tippet should suffice. There have been sightings of Capnia nymphs (super early by two months at least) crawling along exposed banks. Not a ton of them, but it might be worthwhile to throw a little winter stone nymph imitation.
Dry flies – Furimsky BDEs, Griffith Gnats, Parachute Adams, Parachute Midges, Klinkhammers, Parachute Trico Emergers, and CDC Midge Emergers.
Nymphs – Peach Fuzz Jigs, Duracells, Egan’s Iron Lotus, RS-2’s, Booty’s Day-2 Midge Pupa, Zebra Midges, Ice Cream Cone Midges, and Perdigons.
South Fork
As on the Snake, there is decent surface action on the South Fork on the upper reach in Swan Valley and on the lower reaches from Kelly’s Island down to Lorenzo, particularly from 1pm until 4pm (although it can occur as early as noon on warmer days). Slow current riffle pools, seam current margins, backwater side channels are key targets.
Nymph rigs are working in the same water as straight up dry flies. This is especially the case when fishing dry-dropper rigs with tippet in the two to four foot range. Double nymph/triple nymph rigs are producing in deeper eddies and seam lines with four to six feet of leader from trailing nymph to line/suspension device.
Dry flies – Parachute Adams, Renegades, Griffith Gnats, Mating Midges, Snowshoe Tricos, Parachute Midges, CDC Midge Emergers, and Chez’s Krystal Wing Midge Emerger.
Nymphs – Brush Hogs, Duracells, Rainbow Warriors, RS-2s, Zebra Midges, Copper Johns in black or red, Brassies, and Perdigons.