Troutline

Henry's Fork

Idaho·Eastern Idaho·44.30° N, 111.45° W
Flow
10.8 CFS
Henrys Fork near Lake
Water Temp
—
Condition
Below Normal
Weather
33°F
Cloudy

Insights

Sky
Overcast skies
Subsurface streamers and nymphs are favored.
Lunar
New moon tonight
Dark nights — fish are more likely to feed through the day.
Flow
Low flows at 10.8 CFS
Fish are spooky. Lighten tippet and lengthen leaders.
Wind
Wind 16 mph — strong
Shorter casts and heavier flies. Find a bank with cover.
Snowpack
Snowpack 3% of normal
Henry's Fork basin snowpack is at 3% of normal — expect an early runoff and low summer flows, with tailwaters and spring creeks holding up best. The May–July runoff forecast for Henrys Fk nr Ashton is 68% of average.

The Henry's Fork is a spring-fed tailwater that drains the Yellowstone plateau, runs through two big reservoirs (Island Park and Ashton), and reaches its most famous water in the Railroad Ranch stretch of Harriman State Park — six miles of flat, weed-rich, gin-clear current where rainbows in the 14-20 inch range feed selectively on whatever's hatching. The upper river above Island Park Reservoir is small spring creek. Box Canyon below Island Park Dam is fast pocket water full of stoneflies. Below Harriman the river drops through Cardiac Canyon and the Mesa Falls reach. Below Ashton Dam it widens out and the angling pressure thins. It's one of the great year-round fisheries in the West because the spring flows stabilize the river through summer drought and the Island Park tailwater keeps the bottom productive.

How it fishes depends entirely on where you are. Box Canyon is nymph water — heavy stonefly nymphs and rubber-leg patterns drifted through the boulder pockets, with consistent 16-19 inch rainbows when the salmon flies and golden stones come off in late June and July. Harriman is the opposite — slow, technical, sight-fishing dries to selective trout that have seen every Sparkle Dun pattern ever tied. Bring 12-foot leaders, 5x-6x tippet, and the patience to wait for a feeding fish to settle into a rhythm before you cast. The Cardiac Canyon and Mesa Falls reach below Harriman is whitewater with pocket-water dry fly fishing for harder-fighting wild rainbows. Below Ashton Dam through Vernon and Chester the river flattens again and produces big browns on streamers in fall. Best season is mid-June through early October. Salmonfly hatch (Pteronarcys californica) runs late June in Box Canyon. Green drakes are the iconic Harriman hatch in late June and again as Slate Drakes (Drunella flavilinea / Flav) through July. Tricos and PMDs through August. BWOs and mahoganies bring the fall game in September-October.

The corridor is Island Park, ID — a strung-out resort community along U.S. 20 with three established fly shops (TroutHunter in Last Chance, Henry's Fork Anglers in Last Chance, and the Lodge at Henry's Fork), guided trips, and fishing-focused lodging. Rexburg and Ashton serve the lower river. Drive times: 2.5 hours from Bozeman, 5 hours from Salt Lake City, 1 hour from West Yellowstone, 1.5 hours from Jackson. Elevation is 6,200 ft at Island Park — summer evenings are cold and snow stays on the ground into May. Wading is straightforward in Box Canyon but you want studded boots for the round-rock bottom; Harriman wading is mostly in soft weedy current. Regulations vary by section — Harriman State Park is catch-and-release, fly fishing only, barbless hooks, with a June 15 to November 30 season. Box Canyon and the Cardiac Canyon stretch are catch-and-release except for brook trout. The Lower Henry's Fork below Ashton Dam allows harvest. Read the regs board at each access — they change with stretch.

Species

SpeciesAbundanceBest SeasonSizeNotes
Rainbow TroutAbundantJun-Oct12-20"Wild population throughout, with the largest fish in the Harriman stretch where flat water produces selective 18-22 inch fish. Box Canyon densities are very high but average size is 14-17 inches.
Brown TroutCommonSep-Nov12-22"Most common in the lower river below Ashton Dam. Streamer fishing in October produces the biggest fish of the year.
Yellowstone Cutthroat TroutOccasionalJun-Aug10-14"Most cutthroat in the system are in the very upper river above Island Park Reservoir, where they're native. Rare in the famous middle sections.
Mountain WhitefishCommonYear-round10-16"Native and dense in Box Canyon and below Ashton Dam. Hit nymphs aggressively year-round.
Brook TroutOccasionalJun-Sep8-12"Present in the upper river and small tributaries. Box Canyon regulations allow brook trout harvest as the only exception.
Ideal wading flow350–900 CFS
Blow-out>2,200 CFS
Ideal water temp48–62°F

Late June into early July for the salmon fly and green drake hatches. July through August for technical PMD and Trico fishing in Harriman. September into October for BWO, mahogany, and brown trout streamer fishing below Ashton. Avoid early summer if Island Park Reservoir is bottoming out and pushing warm muddy water down through Box Canyon.

Sections

6 sections on this river

Henrys Lake Outlet to Island Park Reservoir

WadeCutthroat · Rainbow Trout

Small spring-creek-style upper river from Henrys Lake outlet through the Mack's Inn / Coffee Pot reach. Native Yellowstone cutthroat and rainbow trout in slow flat water. Fly fishing only above Big Springs. Fishes best in early summer after runoff and before water temps climb.

Best for: Wade fishing small-stream dry flies for cutthroat and rainbow trout — terrestrials and small mayflies in July and August.

Box Canyon

Wade & FloatSalmon · Brook Trout · Rainbow Trout

Three miles of fast pocket water and runs from Island Park Dam down to Last Chance. The headline gauge sits at the top of this section. Catch-and-release except brook trout. Heavy stonefly biomass and dense rainbow populations (14-17 inches average) with bigger fish moved up out of Last Chance.

Best for: Heavy stonefly nymphs through pocket water in June and July. Salmon fly and golden stone dries on warm afternoons late June through mid-July.

Harriman State Park (Railroad Ranch)

WadeRainbow Trout

Six miles of flat, weed-rich, gin-clear current through Harriman State Park. The most famous technical dry fly water in the West. Catch-and-release, fly fishing only, barbless hooks. June 15 - November 30 season. Walk-in access only — foot trails from Osborne Bridge and the park headquarters. Rainbow trout 14-20 inches feeding selectively on mayflies, midges, and Tricos.

Best for: Sight-fishing dry flies to selective rainbow trout. Green drakes, PMDs, Tricos, and BWOs.

Cardiac Canyon to Riverside

FloatBrook Trout · Rainbow Trout

Steep canyon stretch below Harriman where the river drops into faster pocket water and small rapids before settling out at Riverside Campground. Catch-and-release except brook trout. Less pressure than Harriman and bigger, more aggressive wild rainbow trout.

Best for: Float-fishing dry-droppers through pocket water — attractor dries and stonefly nymphs.

Warm River to Ashton Reservoir

Wade & FloatBrown Trout · Rainbow Trout

Below Lower Mesa Falls the river runs through forested canyon past the Warm River and Bear Gulch access points before slowing into Ashton Reservoir. Wild rainbow and brown trout. Standard statewide trout limits apply (2 fish daily). Less famous than Harriman or Box Canyon but quieter and good summer dry fly water.

Best for: Wade fishing pocket water with caddis, PMDs, and hopper-dropper rigs. Brown trout on streamers in September.

Below Ashton Dam to St. Anthony

Wade & FloatBrown Trout · Rainbow Trout

Lower tailwater below Ashton Dam through Vernon and Chester to St. Anthony. Wider, slower, with more brown trout than the upper river. Open to harvest under general Idaho trout rules. Fishes year-round at low winter flows when the upper river is iced or closed.

Best for: Streamer fishing for brown trout in fall. Winter midge fishing when no other section is open.

Regulations

Current fishing rules and restrictions

Regulations vary significantly by stretch. Harriman State Park is catch-and-release fly fishing only with barbless hooks and a June 15 - November 30 season. Box Canyon and Cardiac Canyon are catch-and-release except brook trout. Lower river below Ashton Dam allows harvest under general statewide trout rules.

  • Harriman State Park (lower SP boundary to upper SP boundary): catch-and-release, fly fishing only, barbless hooks, June 15 - November 30
  • Box Canyon (upper Harriman boundary to Island Park Dam): catch-and-release except brook trout, year-round
  • Cardiac Canyon (Harriman lower boundary to Riverside): catch-and-release except brook trout
  • Mesa Falls reach (Riverside downstream to Ashton Reservoir): standard statewide trout limits, 2 trout daily
  • Below Ashton Dam to confluence: 2 trout daily, statewide rules apply
  • Upper river above Island Park Reservoir: 2 trout daily, fly fishing only above Big Springs

The boundaries between regulation sections are signed at access points but easy to misread from a drift boat. The Harriman C&R section is the strictest — flies only, single barbless hooks, no bait or scent at all. Idaho fishing license required statewide for anglers 14+.

Source: Idaho Department of Fish and Game — Fishing Seasons and Rules. Regulations change annually — verify before fishing.

Access & Logistics

Getting there, fly shops, and lodging

Getting There

Island Park, ID

1 hr from West Yellowstone, 1.5 hrs from Jackson, 2.5 hrs from Bozeman, 5 hrs from Salt Lake City

Fly Shops

Lodges

Camping & Lodging

Riverside, Buttermilk, and Big Springs campgrounds on the Caribou-Targhee National Forest. TroutHunter Lodge and Henry's Fork Lodge for fishing-focused stays. Strung-out resort cabins and motels along U.S. 20 from Last Chance south to Ashton.

U.S. 20 parallels the river from Henrys Lake to Ashton. Access at Mack's Inn, Big Springs, Box Canyon (Island Park Dam), Last Chance, multiple Harriman SP trails (foot access only inside the park), Riverside Campground, Warm River, Bear Gulch, Vernon Bridge, and the St. Anthony Sand Dunes. Drift boats put in at Last Chance, Osborne Bridge, Pinehaven, Riverside, and Warm River.

Conditions data is live from public monitoring networks. Regulations change annually — always verify current rules with your state fish & wildlife agency before fishing.

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