Current Flows of the Henry’s Fork

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What is the Henry’s Fork?

The Henry’s Fork is a premier angling destination renowned for its rich fishing history and incredible diversity of opportunities, rivaling even the Madison River in prominence. Stretching over 70 miles, it offers everything from technical flat water sight fishing to fast-moving canyon stretches, catering to anglers of all skill levels.

As the largest spring creek in the United States, the Henry’s Fork is famous for prolific hatches, exceptionally healthy trout populations, and a stunning alpine setting. The seven-mile Railroad Ranch section in Harriman State Park is particularly celebrated for its wide, shallow, crystal-clear waters and large free-rising rainbows, providing one of the finest dry fly fishing experiences worldwide. This stretch is a true test of angler skill and persistence.

The river’s diverse insect hatches include spring baetis, march browns, salmonflies, golden stones, multiple caddis species, pale morning duns, green drakes, tricos, callibaetis, mahoganies, pseudocloeons, fall baetis, and more. This rich bug activity makes it a “bug factory,” presenting anglers with a constant challenge to match the hatch and an excellent place to hone fly-fishing techniques.

Below the Railroad Ranch, the lower Henry’s Fork offers accessible fishing primarily from drift boats, with plentiful brown and rainbow trout that are more willing to take flies. Prime fishing times vary by section: the Railroad Ranch shines from June to mid-July and September through mid-October, while the lower river is best from May to early July during salmonfly and golden stonefly hatches, and again in fall when big browns become active.

Named after Colonel Andrew Henry, an early 19th-century fur trader who explored the region and established Fort Henry near today’s St. Anthony, the Henry’s Fork flows through diverse landscapes including ranch lands, timbered canyons, and spring creek environments. Its tributaries also offer outstanding fisheries.

Known as the “Graduate School of Fly-Fishing for Ph.D. Trout,” the Henry’s Fork challenges anglers with highly selective trout, especially on the Railroad Ranch. However, its variety extends beyond this famous stretch. The Box Canyon below Island Park Reservoir offers exciting tailwater fishing in fast, boulder-filled water, while the Last Chance and Railroad Ranch sections are world-renowned for sight casting opportunities. Downstream of Lower Mesa Falls, brown trout join the rainbow populations, creating dynamic fishing from the Warm River confluence to Ashton, and in tailwaters from Vernon to St. Anthony.

Year-round fishing is supported by abundant aquatic insects such as Blue Wing Olives, Midges, Caddis, and the earliest salmonfly hatch in the Yellowstone ecosystem beginning in May near St. Anthony and progressing upstream. The river’s consistent and varied hatches ensure it remains a top destination through the seasons.

With its combination of trophy trout, prolific insect life, and breathtaking scenery, the Henry’s Fork stands as one of the greatest and most storied fisheries in the world—an absolute must for any serious angler.

The Upper Henry’s Fork

The Henry’s Fork originates at Big Springs, located at the base of the Pitchstone Plateau. This pristine spring creek flows about 5 miles before emptying into Island Park Reservoir. In this upper section, the fishery is varied but less consistent than downstream, offering brook trout, cutthroat trout, occasional kokanee salmon, and rainbow trout.

Below Island Park Dam, the river runs through a three-mile basalt gorge called the Box Canyon. While dry fly fishing is possible seasonally, this stretch is primarily known for world-class nymphing. Anglers can expect challenging, fast water filled with strong, healthy rainbow trout. The canyon, surrounded by National Forest, is also rich in wildlife like eagles, ospreys, and moose.

As the river exits Box Canyon, it slows and widens through Harriman State Park, a former Union Pacific Railroad Ranch donated to Idaho in 1982. This iconic section is a large spring creek with easily wadeable waters and holds large, selective rainbow trout. Many anglers become captivated by this stretch and rarely fish elsewhere.

Melting snow and rain fill the 37-mile-wide Island Park Caldera, creating a vast underground aquifer that forces water up at Big Springs, forming the Henry’s Fork River. Big Springs is accessible from the road, with a boat launch (dock only) downstream at an old railroad trestle. Fishing is prohibited from Big Springs to the Henry’s Lake Outlet, but this stretch can be accessed by launching at the Henry’s Lake Outlet (unimproved boat slide).

The float from Big Springs to Mack’s Inn (3.9 miles) is a slow meander through open mountain views with frequent moose and waterfowl sightings. Wade access is possible through National Forest land near Mack’s Inn, where a public take-out lies upstream of the Hwy 20 bridge. Downstream are Upper and Lower Coffee Pot rapids, which are impassable, and floating is not permitted beyond Mack’s Inn.

From Mack’s Inn, the river gains speed through Upper and Lower Coffee Pot Rapids. Wade access is available via Coffee Pot Campground and nearby forest roads. Below the rapids, the river is bordered by private property, preventing floating.

The estuary where the Henry’s Fork enters Island Park Reservoir is accessible by a boat ramp on the south side of the Yale-Kilgore bridge (river left) through the campground. Motorized boats are prohibited upstream of the bridge, but rowing is allowed, and wade access is limited.

The Henry’s Fork resumes below the Island Park Reservoir dam, soon joined by the Buffalo River. A boat ramp lies just downstream (river left). This section features swift rapids and lava boulders, making wading difficult at higher flows (>1,000 CFS) and boating tricky at low flows (<400 CFS). Special fishing regulations apply here. A trail along river left runs from the Buffalo River dam to Last Chance, enabling wade access. The Last Chance boat ramp is 5.5 miles downstream.

Between Last Chance and Osborne Bridge, wade access is largely unimpeded due to Harriman State Park, which has special regulations and a distinct fishing season. This famous stretch fishes like a classic spring creek, with large rainbows feeding on dry flies drifting through swirling currents.

The Middle Henry’s Fork

Downstream of the Ranch, the Henry’s Fork carves through the edge of the ancient Yellowstone supervolcano’s caldera and extends toward the Snake River Plain. This transition zone features several whitewater float stretches with consistent action on fair to medium-sized trout, mostly rainbows, along with some very large specimens. The water varies from fast riffles to high-gradient whitewater, offering fun fishing for opportunistic trout.

Two primary waterfalls, Upper and Lower Mesa Falls, each drop nearly 100 feet and are well worth visiting and photographing. Once the river flattens at the downhill edge of the caldera, it is joined by the Warm River, a spring creek tributary. This creates eight miles of relatively easy-to-fish riffle water, ideal for beginners, ending at Ashton Reservoir.

The Osborne Bridge boat ramp (river right) lies within Harriman State Park and is subject to special regulations and a separate fishing season. The easiest river crossing under the ATV bridge is on river left. At the north end of the Pinehaven Subdivision, the topography changes, and an unimproved public boat slide is accessible by Wood Rd 16 (river left, 2.8 miles). Because Wood Rd 16 is rough, many float further to Riverside Campground (6.3 miles) with its improved boat ramp (river right).

Wade access from Osborne to Wood Rd 16 is easy. After Wood Rd 16, river right is private land while river left is National Forest; both sides become public again near Riverside Campground. The float between Wood Rd 16 and Riverside gains speed as it enters a boulder-strewn canyon.

Riverside Campground’s boat ramp (river right) leads immediately into faster, boulder-filled water, indicative of the float down to Hatchery Ford boat ramp (river left, 5.3 miles). This remote section is nearly continuous rapids and very technical, best suited for expert boaters and rafts. Wade access is good at Riverside and Hatchery Ford, but access between them is difficult despite being in National Forest.

Downstream of Hatchery Ford, a series of small waterfalls lead to Upper and Lower Mesa Falls—none are boatable, so don’t miss the takeout. The road to Hatchery Ford can be rough.

This section features fast rock gardens separated by calm water and is only open to rafts. The boat slide here is very steep and rocky. Launch from Lower Mesa Falls campground, then park in the visitor lot and walk back to your boat to start the canyon float on river left. About 0.75 miles downstream is Surprise Falls; the safest line runs down the river right tongue, followed by a challenging rock garden at lower flows.

This remote National Forest section has limited access, with the best wade option at Stone Bridge parking lot. The takeout is an improved boat ramp at Stone Bridge (6.7 miles), just downstream of Fishermans Dr bridge on river right.

Stone Bridge boat ramp offers two takeout options: Jump-off Canyon (river right, 6.5 miles), upstream of Hwy 20 bridge where current slows near Ashton Reservoir—good on windy days—and Fremont County Boat Dock (river right, 7.4 miles), downstream of Hwy 20 bridge, which also launches power boats. All these access points, including one 0.5 miles upstream from Jump-off, allow wade access, but land between them is mostly private, limiting wading opportunities.

The Lower Henry’s Fork

After the river passes the town of Ashton, Idaho, and exits Ashton Reservoir, several remarkable fisheries begin. These lower river sections, separated by diversion dams, offer great dry fly opportunities and strong hatches that drive the fly fishing action.

The river winds through farmland dotted with old volcanic features, while the Teton Range towers to the east, providing spectacular vistas. Fishing here favors quality over quantity, as catch rates can be lower but the rewards larger. This stretch holds trophy brown trout and large rainbows, offering excellent seasonal fishing, typically best in May and June, and again from September through October.