Henry's Fork of the Snake River Fishing Guide

The Henry's Fork is one of the best-known trout rivers in the West, with very different water from top to bottom. Box Canyon below Island Park Dam is fast water with many rainbows, while the Ranch in Harriman State Park is slow, clear, spring-creek-like water with picky trout. Each section has its own rules, so read the Idaho Fish and Game section list before you fish.

📍 Eastern Idaho. Box Canyon is just below Island Park Dam near the town of Island Park; Harriman State Park (the old Railroad Ranch) is downstream, about 28 miles south of West Yellowstone, Montana. Below Mesa Falls the river runs on past Ashton toward its meeting with the South Fork Snake.

Map: spots, ramps and marinas

★ Fishing hot spot · ● Boat ramp · ● Marina · ▭ Protected area (solid red = no fishing, dashed = fishing with rules)

Open the full Rocky Mountain Trout Rivers map →

Quick facts

About 8 miles of the Henry's Fork run through Harriman State Park, known to anglers as "the Ranch."
The Railroad Ranch became Harriman State Park on April 1, 1977, and the park opened to the public in 1982.
The Harriman Ranch section is closed to fishing December 1 through June 14 and opens June 15 for catch-and-release, fly fishing only, with barbless hooks.
Idaho Fish and Game counted 4,209 rainbow trout per mile in Box Canyon in 2021; the earlier long-term average was 3,103.
Idaho's state record brown trout, 27.31 pounds, came from Ashton Reservoir on the Henry's Fork in 2007.

What you can catch

Rainbow trout
Main fish in Box Canyon and the Ranch; catch-and-release in those sections.
Brown trout
Found with rainbows below Mesa Falls; state record came from Ashton Reservoir.
Brook trout
Can be kept in some catch-and-release sections (rules say "except Brook Trout").
Cutthroat trout
No harvest of cutthroat in many Henry's Fork sections.
Mountain whitefish
Upper Snake Region whitefish limit is 25 unless a section rule says otherwise.
Yellowstone cutthroat trout (South Fork Snake)
The South Fork Snake has Idaho's largest river population of native Yellowstone cutthroat; no harvest of cutthroat there.

Month by month

January	Box Canyon open (catch-and-release, no bait, barbless). The Ranch is closed.
February	Box Canyon open. Ranch closed. Winter dam releases affect young trout in Box Canyon.
March	Box Canyon open. Ranch closed.
April	Box Canyon open. Ranch closed.
May	Box Canyon open. Harvest season opens Saturday of Memorial Day weekend on some lower sections (Vernon Bridge to Ashton Dam).
June	Salmonflies and golden stones in Box Canyon and the canyon water. Ranch opens June 15: PMDs, caddis, then green drakes and flavs.
July	Ranch open (catch-and-release, fly fishing only). Check local fly shop hatch reports.
August	Ranch and Box Canyon open. Check flows and hatch reports.
September	Ranch open. Elk bugle in Harriman State Park in the fall.
October	Ranch open through November. Check flows and hatch reports.
November	Ranch open through November 30. Vernon Bridge to Ashton Dam goes back to catch-and-release after Nov 30.
December	Ranch closes December 1. Box Canyon stays open.

Tips

Anyone 14 or older needs an Idaho fishing license.
In Box Canyon, indicator nymphing is the most steady method; keep stonefly dries handy in June.
At the Ranch, bring spinners, emergers and plenty of 4X-5X tippet, and greet other anglers before you fish near them.
Box Canyon is best fished by boat; some paths lead down from the old road west of US 20.
Below Ashton expect heavy boat traffic in summer; fish with courtesy.

Rules and license

Idaho Department of Fish and Game (Upper Snake Region) · Official rules page ↗

License: anyone 14 or older must have an Idaho fishing license. Check current fees with IDFG.
Harriman Ranch (lower to upper Harriman State Park boundary): closed Dec 1 - June 14; June 15 - Nov 30 trout catch-and-release, fly fishing only, barbless hooks.
Upper Harriman boundary to Island Park Dam (Box Canyon area): trout catch-and-release (except brook trout), no bait, barbless hooks.
Riverside Campground boundary to lower Harriman boundary: trout catch-and-release (except brook trout), no bait, barbless hooks.
Highway 20 bridge to Riverside Campground boundary: trout limit 2, no harvest of cutthroat.
Vernon Bridge to Ashton Dam: catch-and-release Dec 1 - Friday before Memorial Day weekend; then trout limit 2, no cutthroat harvest.
Closed in Harriman State Park: Golden Lake, Silver Lake and Thurmon Creek. Henrys Lake Outlet to the head of Big Springs is closed.
South Fork Snake: no harvest of cutthroat, brown trout limit 2, no limit on rainbow trout or hybrids.

Rules change. Always check the official page before you fish.

Boat ramps and marinas

The map above shows 8 boat ramps and 0 marinas from OpenStreetMap. Tap any dot for directions.

West End Boat Ramp

Sources

Checked October 2026. BigJoe does not invent facts: every number on this page comes from the sources listed above.