Henry's Fork River Idaho Hatch Chart
Southeast Idaho, from the outlet of Henry's Lake and Island Park Reservoir through the renowned spring creek and freestone sections to its confluence with the Snake River near Rexburg. The Henry's Fork of the Snake is one of the most celebrated trout rivers in North America - a large-volume spring creek with extraordinary water clarity, prolific hatches, and notoriously selective wild rainbow trout. The river divides into distinct sections with different characters, access conditions, and hatch timing.
Check current Idaho Department of Fish and Game regulations before you go. The Henry's Fork has special regulations including catch-and-release-only sections, artificial lures and flies only restrictions, and seasonal closures that vary by section. Verify current rules for your target water before fishing.
Shop by type: dry flies, nymphs, Euro nymphs, hoppers and terrestrials, streamers.
The four sections
Box Canyon - Island Park Dam to Last Chance
A powerful, cold freestone run dropping through a basalt canyon below Island Park Dam. Deep, fast water with large boulders and complex currents. Wild rainbows averaging 14-18 inches with larger fish throughout. The Box Canyon fishes best with nymphs and streamers - it lacks the spring creek character of the sections below but produces big fish and heavy hatches of salmonflies and golden stones in June. Less technical than the Harriman but more demanding wading. Catch-and-release, artificial only.
Last Chance and the Harriman Ranch - Railroad Ranch
The iconic section. From Last Chance downstream through the Harriman State Park (Railroad Ranch), the Henry's Fork transforms into a wide, flat spring creek with extraordinary clarity and painfully selective trout. Fish average 16-20 inches and see every angler on the river. The green drake hatch in late June and early July is the most famous hatch event in American fly fishing - massive flies, rising fish everywhere, and extraordinarily difficult presentations. PMDs, tricos, and callibaetis fill the rest of the season. Catch-and-release, artificial only through the Ranch.
Cardiac Canyon - below Harriman
Below the Ranch the river drops into Cardiac Canyon - a remote, rugged freestone gorge accessible only by a long hike or horseback. Far fewer anglers, less technical fishing, and strong populations of wild rainbows and browns. Streamer and hopper fishing excel here. The canyon gets its name from the demanding access, not the fishing - which can be some of the best on the river for those willing to make the walk.
Lower Henry's Fork - Ashton to confluence
Below Ashton Reservoir the river slows and braids through agricultural land before joining the Snake. Warm water temperatures and different character - brown trout and some rainbows. Fall caddis and October caddis fishing can be strong. Less pressure and a different experience from the upper sections.
The green drake hatch
The Harriman Ranch green drake hatch is the defining event of the Henry's Fork year and one of the most anticipated hatch windows in fly fishing. Drunella grandis - western green drakes - emerge in large numbers from late June into mid-July on the Railroad Ranch and Last Chance water. The combination of large flies (size 10-14), clear slow water, and selective fish makes this one of the most challenging and rewarding dry-fly experiences available anywhere. Fish the emerger and dun during the hatch window, typically midday to early afternoon. Presentation and drag-free drift are everything - the fish have seen every pattern available.
- Time your trip for the last week of June through the first week of July for peak green drake activity.
- Fish the emerger first, then switch to the dun as fish begin taking off the surface confidently.
- Long leaders (12-16 feet), fine tippet (5X-6X), and reach casts are essential on the Ranch.
Year at a glance - Harriman Ranch / Last Chance (trout)
| Month | Primary hatches | Also carry | Typical sizes |
|---|---|---|---|
| Jan | Midges | Small nymphs | 18-24 |
| Feb | Midges, BWO | Small nymphs | 18-22 |
| Mar | BWO, midges | Early caddis | 16-22 |
| Apr | BWO, caddis | March Brown, nymphs | 14-20 |
| May | BWO, caddis, PMD start | March Brown | 14-20 |
| Jun | PMD, green drake, caddis | Flavs, yellow sally | PMD 16-18, drake 10-14 |
| Jul | Green drake, PMD, trico | Callibaetis, hoppers start | Drake 10-14, trico 20-24 |
| Aug | Trico, PMD, hoppers | Callibaetis, ants, beetles | Trico 20-24, hopper 8-12 |
| Sep | BWO, trico, hoppers | Mahogany dun, callibaetis | BWO 16-20, trico 20-24 |
| Oct | BWO, mahogany dun | October caddis, midges | BWO 16-20, caddis 8-10 |
| Nov | BWO, midges | Small nymphs | 18-22 |
| Dec | Midges | Small nymphs | 18-24 |
Year at a glance - Box Canyon (freestone)
| Month | Primary hatches | Also carry | Typical sizes |
|---|---|---|---|
| Jan | Midges | Stonefly nymphs | 18-24 |
| Feb | Midges, BWO | Stonefly nymphs | 16-22 |
| Mar | BWO, early stonefly | Stonefly nymphs | 16-22 |
| Apr | BWO, caddis, stonefly nymphs | March Brown | 14-20 |
| May | Caddis, BWO, stonefly nymphs | PMD late month | 14-18 |
| Jun | Salmonfly, golden stone, caddis | PMD, yellow sally | Stones 4-10, caddis 14-16 |
| Jul | Caddis, PMD, yellow sally | Hoppers start, streamers | 14-18 |
| Aug | Caddis, hoppers, ants | Streamers, trico | Hopper 8-12, caddis 14-16 |
| Sep | BWO, caddis, hoppers | Streamers, mahogany dun | BWO 16-20, hopper 8-12 |
| Oct | BWO, October caddis | Streamers, midges | BWO 16-20, caddis 8-10 |
| Nov | BWO, midges | Stonefly nymphs | 18-22 |
| Dec | Midges | Stonefly nymphs | 18-24 |
January
Harriman/Last Chance: Midge fishing on the flat spring creek water. The Ranch is quiet in January but fishable on mild days. Fish hold in the deeper channels and along undercut banks. Technical presentations on fine tippet.
Box Canyon: Midge program and stonefly nymphs. The canyon holds fish year-round but January is slow. Focus on slower water adjacent to fast runs.
- Midges - 18-24. Red zebra midge or small Euro nymph in slow seams.
- Stonefly nymphs 6-10 in the Box Canyon.
February
Harriman/Last Chance: BWO begin on gray afternoons. One of the few rivers where February can produce rising fish on the right overcast day - the spring creek character keeps water temperatures stable. Midge program continues.
Box Canyon: BWO and midges. Stonefly nymphs remain productive subsurface.
- BWO - 18-22 on overcast afternoons. Parachute BWO when fish are rising.
- Midges and small nymphs subsurface.
March
Harriman/Last Chance: BWO hatches strengthen and become more reliable through March. The spring creek sections produce consistent afternoon hatches when conditions are right - overcast, mild, low wind. Early caddis begin on the warmer sections by late month.
Box Canyon: BWO and early stonefly activity. Stonefly nymphs remain the primary subsurface option.
- BWO - 16-20. Parachute BWO and CDC Baetis emerger on the Ranch water.
- Stonefly nymphs 6-10 in the Box Canyon from nymphs.
April
Harriman/Last Chance: Caddis and BWO overlap through April. March Browns appear on the broader water. This is the beginning of the pre-season build on the Ranch - fish are becoming more active and rising more consistently. PMDs can begin in late April in warm years.
Box Canyon: Caddis and BWO with stonefly nymphs subsurface. The Box Canyon wakes up significantly in April as flows stabilize.
- BWO and March Brown on overcast days. Parachute BWO.
- Caddis - 14-16. Elk hair caddis evenings.
- Stonefly nymphs in the Box Canyon.
May
Harriman/Last Chance: The season builds quickly in May. BWO continue on overcast days, caddis in the evenings, and PMDs begin by mid to late month on the Ranch water. May is an excellent time to visit - fish are active, crowds are lighter than peak summer, and the river is fishing at its best before the green drakes arrive.
Box Canyon: Caddis dominate with stonefly nymphs subsurface. Late month PMD begins in the calmer sections. Runoff timing affects the Box Canyon - check flows before planning a May trip.
- BWO on overcast mornings. Parachute BWO.
- Caddis - 14-16 afternoons and evenings. Elk hair.
- Late May: first PMD - 16-18. Pale Morning Dun.
- Stonefly nymphs in the Box Canyon.
June
Harriman/Last Chance: The most anticipated month on the Henry's Fork. PMDs begin in earnest in early June and the green drake hatch arrives in the last week of the month. The Railroad Ranch in late June is the premier dry-fly event in American fly fishing - book well in advance, arrive with long leaders and fine tippet, and expect humbling refusals from impossibly large trout. Flavs (small western green drakes) overlap with the larger drakes. Yellow sallies in faster water.
Box Canyon: The salmonfly hatch hits the Box Canyon in June - typically mid to late month after the canyon warms from spring runoff. Golden stones follow. This is the best month for big fish on big dries in the Box.
- PMD - 16-18. Pale Morning Dun mornings on the Ranch.
- Green drake - 10-14. Western green drake - fish the emerger first, then the dun. Last Chance and Railroad Ranch, late June into July.
- Salmonfly (Box Canyon) - 4-8. West Fork Salmonfly hard against the canyon walls.
- Golden stone (Box Canyon) - 6-10. Drop a stone nymph below a dry.
- Caddis evenings. Elk hair.
July
Harriman/Last Chance: The green drake hatch continues into the first week of July, then transitions to tricos and continuing PMDs. Trico spinner falls on the flat Ranch water are technical and rewarding - early morning, size 20-24, fine tippet. Callibaetis begins on the slower sections and adjacent ponds. Hoppers start appearing along the bank vegetation by mid-month. July is the busiest month on the Ranch - expect other anglers.
Box Canyon: Caddis, PMDs, and yellow sallies in the riffles. Hopper fishing begins along the grassy banks. Streamers for big fish in the deeper canyon slots.
- Early July: green drake continuing - western green drake dun and emerger.
- Trico - 20-24. Early morning spinner falls on the Ranch. Fine tippet essential.
- PMD - 16-18. Pale Morning Dun mornings.
- Callibaetis - 14-16 on slower water and ponds. Callibaetis sparkle dun.
- Early hoppers along the banks - hoppers and terrestrials.
August
Harriman/Last Chance: Trico spinner falls are the morning anchor of August on the Ranch - often the most reliable rising fish of the day. PMDs continue. Hoppers along the bank and in the foam lines. Ants and beetles fill in midday. Callibaetis on the slower sections. One of the best months overall despite the summer heat - early morning trico fishing with hoppers in the afternoon is the classic August Henry's Fork day.
Box Canyon: Hoppers along canyon walls, caddis in the evenings, streamers for big fish. August can produce excellent streamer fishing in the Box as fish become more aggressive.
- Trico - 20-24. Morning spinner falls on the Ranch.
- PMD - 16-18. Pale Morning Dun mornings.
- Hoppers, ants, beetles - hoppers and terrestrials. Hopper-dropper with a small nymph along the banks.
- Callibaetis - 14-16 on slower water. Callibaetis sparkle dun.
- Streamers in the Box Canyon for aggressive August fish.
September
Harriman/Last Chance: Outstanding month. Crowds thin dramatically after Labor Day and the fishing improves. BWO return strongly as nights cool - the fall olive hatches on the Ranch rival the spring. Tricos continue into mid-September. Mahogany duns add an afternoon option on overcast days. Hoppers through mid-month. Callibaetis on the ponds and slow sections.
Box Canyon: BWO and caddis with hoppers through mid-month. Streamer fishing picks up as fall approaches and big fish become more aggressive.
- Trico through mid-September on the Ranch. Early morning spinner falls.
- Hoppers and ants through mid-September. Hoppers and terrestrials.
- BWO - 16-20. Parachute BWO and CDC Baetis emerger.
- Mahogany dun - 14-16 on overcast afternoons.
- Callibaetis - 14-16 on slower water. Callibaetis sparkle dun.
October
Harriman/Last Chance: Fall BWO fishing on the Ranch is exceptional - dense hatches on gray afternoons with selective but catchable fish. Mahogany duns overlap with the olives. October caddis add a larger dry-fly option. One of the least crowded and most productive months of the year on the Henry's Fork.
Box Canyon: BWO and October caddis for trout. Streamer fishing for big browns moving in fall.
- BWO - 16-20. The dominant hatch on the Ranch.
- Mahogany dun - 14-16 on overcast afternoons.
- October caddis - 8-10 in the Box Canyon and lower sections.
- Streamers for fall browns in the Box Canyon.
November
BWO and midges on both sections. The Ranch is quiet and productive on mild days. The Box Canyon fishes well for the angler who has it to themselves - stonefly nymphs and midges produce fish through the month.
- BWO - 16-20 on overcast afternoons. Parachute BWO.
- Midges - 18-24 in slow seams.
- Small nymphs subsurface.
- Stonefly nymphs in the Box Canyon.
December
Midge and BWO program on both sections. The spring creek character of the Ranch keeps temperatures stable and December can produce midday rising fish on the right day. Access to the Ranch may be limited in winter - check Harriman State Park conditions before making the trip.
- Red zebra midge and small nymphs - 18-24.
- BWO on overcast afternoons. Parachute BWO.
- Stonefly nymphs in the Box Canyon.
A western dry and nymph assortment covers the core season on both sections. Add trico patterns and callibaetis imitations for the Ranch in summer, a green drake dun and emerger for late June and early July, and a salmonfly pattern for the Box Canyon in June. The Henry's Fork rewards patience, preparation, and the humility to accept refusals from the most educated trout in Idaho.