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Idaho's Henry's Fork Rebound

Idaho's Henry's Fork has made significant steps toward recovery. The fishing and the quality of fish have improved significantly.

Idaho's Henry's Fork Rebound
The author ties on a fly at Osborne Bridge. The river there is like a giant spring creek with soft currents, easy wading, prolific hatches, and many large rainbows. You must plan your approach, match the hatches, wade careful, and cast accurately to catch the fish. Photo: James H. Nelson/Mountain Sports Photos

I read with great surprise that the readers of Trout magazine recently had picked Idaho's Henry's Fork as the best trout stream in America. I was also surprised to learn that in the April 1999 issue of Sports Afield, the Henry's Fork was rated as one of the top ten fishing rivers in the country. Twenty years ago, these ratings would not have surprised me, but since its heyday in the late 1970s and early '80s, the Henry's Fork has had some tough times. As the ratings suggest, however, the river has made significant steps toward recovery.

The 12-mile stretch from Island Park Dam to the Pinehaven summer home area is once again a quality fishery that offers a variety of angling challenges, from large sippers in smooth spring-creek-like flows to fast pocketwater action among the rocks. This stretch includes the Box Canyon and the famous Harriman State Park, also known as the Railroad Ranch.

Henry's Fork Rebound
There are several species of Baetis that dribble out through the season and morning Tricos and Callibaetis set the table for trout in late summer and early autumn. (R. Valentine Atkinson/Frontiers photo)

Henry's Fork Decline

In 1978 the 4-mile-long Box Canyon stretch alone supported more than 18,000 trout! On the Railroad Ranch, pods of large trout sipped mayflies and caddis in the soft currents where the water is seldom more than waist-deep and anglers can stalk trout from bank to bank. By the mid-1980s, however, Henry's Fork regulars noticed a decline in the quality of fishing. The Idaho Department of Fish & Game confirmed the decline when it reported a drop in the trout population.

Several factors may have contributed to the decline. Grazing cattle destroyed the river's lush undercut streambanks. Water releases from Island Park Dam were inadequate during cold winter months. Wintering trumpeter swans almost completely destroyed aquatic vegetation during low-water years. Several drawdowns of Island Park Reservoir resulted in flows that scoured the streambed and removed aquatic vegetation and insect life. A particularly devastating drawdown in September 1992 flushed more than 50,000 tons of silt and mud into the Henry's Fork, further damaging an already decimated fishery.

Fortunately, the Henry's Fork Foundation and other groups have worked to improve the river's fishery, primarily by increasing flows from Island Park Dam and opening spawning habitat above a dam on the Buffalo River, an important tributary.

A Great River Today

I have spent my entire life on the Henry's Fork and have fished it from its source down to its confluence with the South Fork of the Snake River—almost 100 miles of water. I believe it offers more diversity of water types than any river in the world and it is not a river that can be discussed in generalities.

Most of the attention given to the Henry's Fork over the years has focused on the section below Island Park Reservoir and its dam, including Box Canyon and Harriman State Park. This section is only a fraction of the entire watershed, and visiting anglers must realize that the Henry's Fork offers much more. While the Railroad Ranch water now offers some of the finest dry-fly fishing in the country, there are other stretches that also offer good fishing for large trout.

The Henry's Fork has four major tributaries—the Buffalo, Warm, Fall, and Teton rivers—all of which provide quality angling opportunities. And it has two reservoirs—Island Park Reservoir and Henry's Lake—both of which provide great fly fishing for big trout. With so many different types of water, there is something for everyone.

The upper section, from Henry's Lake to Island Park Reservoir, is the least productive stretch of the river. It is managed as a put-and-take fishery and stocked heavily with hatchery trout at the popular access points. It receives a substantial migration of spawning trout from Henry's Lake early in the season and from Island Park Reservoir in autumn.

The river has two different tailwater stretches, the Box Canyon below Island Park Dam and the productive stretch below Ashton Dam. There is also a deep canyon stretch where the water drops over 1,000 feet in elevation in about 20 miles. There are three major waterfalls in this stretch; the tallest is Upper Mesa Falls which falls more than 100 feet.

The lower section from St. Anthony to the confluence is like many other great Western trout streams, with many large runs, fast riffles, and deep pools. It snakes its way through vast cottonwood bottoms to join the South Fork to form the main Snake River.

The Box Canyon on Henry's Fork

The Box Canyon water is a fine fishery with a good population of chunky, powerful rainbows. The popular salmonfly hatch starts in the "Box" by the first week of June and provides exciting dry-fly action. The big lunkers are likely to hold in the fast runs in the middle of the river and will come up through heavy currents to smash an adult salmonfly. After the salmonfly hatch, the smaller golden stones continue to produce dry-fly fishing until the end of July.


The dry-fly fishing is normally spotty during the remainder of the season. Weighted nymphs and streamers, fished deep in the runs, frequently produce the best trout. You don't need to use large, heavily weighted stonefly nymphs to catch large trout consistently, though. I have found that small #16-#18 bead-head patterns such as the Prince Nymph, Pheasant-tail Nymph, and Serendipity usually out-produce bigger nymphs, especially during summer. My best success with streamers has been in the early morning and late evening, and my favorite time to fish them is in the fall. Sculpins, Zonkers, and Woolly Buggers normally do the job.

The Box Canyon has good access for anglers on foot as well as float fishermen, and it gets a lot of traffic, especially from floaters. Anglers should use proper fishing etiquette to avoid conflicts on this narrow river. There is a nice Forest Service campground near the upper end.

Harriman State Park (Railroad Ranch)

The only view many anglers have of the Henry's Fork is the Railroad Ranch. It isn't for everybody. The stories of frustrated anglers hurling their rods into the river or an angler fishing over the same rising trout for four hours without results are true. All I know is that if I could design a great dry-fly stream, with soft flowing currents, easy wading, prolific aquatic insect hatches, and giant rising trout, this would be it.

One of the biggest challenges is locating fish. The river all looks the same for about seven miles from Last Chance to below the Osborne Bridge at Pinehaven. It is a spring creek of gigantic proportions, but not much of it is more than three feet deep. The population of big, fat rainbows is up. The numbers may not be as high as they were in the 1970s, but there are plenty of big trout and they're as tough to catch as ever. They aren't everywhere, though. They like to hang out in certain areas, and it takes a little experience to discover those places.

Once you locate a big rising trout, you must plan a careful approach. If you alert the fish by careless wading or bad casting, you probably won't put it down. Instead, the fish will probably just cruise away, continuing to rise as it goes.

Henry's Fork Rebound
The lower Henry's Fork near St. Anthony is like many other great Western trout streams, with many runs, fast riffles, and deep pools. Access below St. Anthony is more difficult, but the water does not have the summer crowds that are common at Harriman State Park. (James H. Nelson/Mountain Sports photo)

Selecting the proper fly is only a small part of the puzzle. You've got to be able to put the fly in the fish's feeding lane and do it enough times until your presentation coincides with the trout's rising rhythm. Even if you have a good eye for what is on the water, you'll need to determine whether the trout is taking something on the surface, in the surface film, or just under the surface. After you do it all right and hook a fish, you may discover that the next trout is on a completely different program. That's what makes the ranch what it is. Nobody catches many fish there. It just isn't that kind of a place.

No other section of river produces such a variety or density of aquatic insects. There are four or five species of caddis that hatch early in the season, and a bunch more that hatch in August and September. There are also several mayfly hatches in full swing when the Ranch opens on June 15. Like most spring creeks, the Pale Morning Dun (Ephemerella inermis, PMD) is the crank that turns the wheel on the mayfly hatches. There are always PMDs hatching somewhere on the Ranch from Opening Day until mid-October. They get smaller as the season wears on, from #16 at the start down to #20 by the end.

The largest mayflies usually start showing up by the third week of June. The Green Drake (Drunella grandis) may be the most famous hatch on the Henry's Fork, but it is frequently a disappointment. The best hatches occur around midday on overcast days. These are big, fat mayflies, and when they come out, you'll see explosive rises. The best patterns are duns, emergers, and cripples in #10 or #12. The Brown Drake (Ephemera simulans) is even bigger and usually emerges just before dusk.

I think the most underrated mayfly hatch is the "Flav" hatch (Drunella flavilinea). These robust mayflies are a close cousin to the larger Green Drakes. They look almost exactly like Green Drakes except they are a couple of sizes smaller, and it doesn't take many of them on the water to put the trout into a feeding frenzy. They start emerging in the afternoon toward the end of June and continue for several weeks. This past season, they hatched until almost the end of August!

There are several species of Blue-winged Olive mayflies (Baetis, BWO) that dribble out all through the season. They really start to intensify by summer's end and provide the bulk of the dry-fly fishing in October and November. Tricos (Tricorythodes minutus) and Callibaetis (Callibaetis ferrugineus) are two more important mayfly species that produce some excellent morning fishing from late summer into early autumn. These mayflies are joined by some great hatches of Mahogany Duns (Paraleptophlebia bicornuta) in September.

Terrestrials are equally significant, and no angler in his right mind would ever attempt to fish the Harriman Park stretch without a good supply of ants, beetles, hoppers, and crickets.

Lower Canyon Water

A 20-mile section of the Henry's Fork receives very little fishing pressure, despite good access. The water tumbles through a deep canyon from Riverside Campground to the confluence at Warm River. Access is from several Forest Service roads, but it is a hike-in proposition that requires a climb up the steep canyon after a hard day of fishing. The hatches and tactics for this stretch are much like the Box Canyon. If you're in good physical condition, it's a good place to get away from the crowds.

Below Warm River the canyon opens up a little, and there is road access for most of the way from there down to Ashton Reservoir. There are some big browns here and they are most often caught early in the season, during the salmonfly hatch, and later with streamers. Lower Mesa Falls is a natural barrier that keeps the fish from moving farther upstream.

Ashton Tailwater

The Lower Henry's Fork gets a major boost in productivity below the Ashton Dam. This water is as productive as any other major Western tailwater, and its hatches are intense, with big stoneflies starting off the season around Memorial Day. Later on, there are intense caddis hatches that continue until early July. This lower section gets many of the same mayfly hatches as Harriman State Park, including PMDs, Green Drakes, Flavs, Mahogany Duns, and BWOs.

It doesn't get Brown Drakes, but the Grey Drakes (Siphlonurus occidentalis) more than make up for it. The duns aren't much of a factor, because they crawl out to emerge in the sloughs, irrigation ditches, and margins of the stream. The spinners swarm to the river in such numbers that you have to experience it to believe it! The big trout come from everywhere to feed on them. They normally start getting on the water in the early afternoon and continue until late evening. This activity takes place from mid-June until early July, the same time that most anglers are trying to catch up to the Green Drake hatch upstream at the Harriman Ranch. Some anglers use intricate patterns to imitate the Grey Drake Spinner, but I still haven't found a pattern that is better than a #10 Parachute Adams.

The fishing is good all the way past St. Anthony to the confluence with the Snake near Rexburg. The access gets a little tricky below St. Anthony.

Idaho's stream access law is similar to Montana's. You can legally walk along the river within the high-water mark as long as you enter the river from a public access point. Even though most of the Henry's Fork from Ashton downstream flows through private property, there are plenty of good places to access the river. So far, visiting anglers have treated landowners well and it is rare to get turned down if you ask permission to fish.

The river channels out below St. Anthony and braids its way through some magnificent cottonwood bottoms. You can work down a side channel and think you're lost until you emerge hours later and find yourself only a few hundred yards from your car. You're also likely to see a moose, whitetail deer, or a bald eagle.

The lower river has benefitted from better stream flow management and more-restrictive fishing regulations. There is no place like Harriman State Park, and I fish it as often as I can after the crowds thin out in July. I don't fish there in June during the Green Drake hatch because the river near my home in St. Anthony offers some first-rate dry-fly fishing with a lot more solitude. This past season, the fishing around St. Anthony was the best I can remember.

Henry's Fork Rebound
The Henry's Fork at Harriman State Park may have the best dry-fly fishing in the country, but other sections, including the lower river, also have good hatches and large, wild trout. (James H. Nelson/Mountain Sports photo)

Four Good Tributaries of the Henry's Fork

The Teton and Fall rivers are major river systems that you could spend an entire season trying to learn. They are both blue-ribbon trout streams and would probably be household names if they didn't flow in the shadow of the Henry's Fork. In recent years I have rekindled a relationship with Fall River and its respectable trout. It is a freestone stream that normally doesn't come into its own until midsummer. My favorite way to fish it is to use an attractor dry fly with a nymph dropper.

The Buffalo and Warm rivers are smaller streams and offer great small-stream backcountry fly fishing for pan-size trout. Both of these streams offer great family fishing opportunities and good camping. They are both spring-fed streams that provide significant spawning habitat for Henry's Fork trout.

Timing Your Visit to Henry's Fork

The fishing season can be complicated in Idaho. We have progressive fishing regulations that provide a lot of catch-and-release water in the Box Canyon and Harriman State Park, and a slot limit from the park downstream to St. Anthony. The fishing seasons are a little backward, however. The Henry's Fork doesn't have enough open water for year-round fishing. The general Idaho season doesn't open until the Saturday of Memorial Day weekend, and it closes November 30. The Harriman Park water opens later on June 15 and closes September 30. There is some year-round fishing downstream of Ashton, but you must read the regulations carefully if you plan to fish during the off-season.

I wouldn't make a special trip to fish the Henry's Fork in winter or early spring, but the fishing can be exceptional if you hit the right weather. Midges are usually on the water every day, and plenty of trout feed on them. There are good Baetis hatches in March and April, followed by a larger Western March Brown (Rhithrogena morrisoni). The "Mother's Day" caddis hatch also occurs on the Henry's Fork in April and continues until the salmonflies start to show in late May.

The winter and spring fishing can be crowded, especially on the weekend, because of the limited amount of open water. Idaho's winters can be cold and nasty, but if you like to ski or you're here on business, don't forget your fly rod!

Is the Henry's Fork back? If you look at the entire watershed, I think it is. While the Box Canyon and Railroad Ranch may never show the trout numbers of the 1970s, the quality of the fish and the fishing is better than ever. At least now if you're lucky enough to catch a 20-inch trout, you'll know it is a wild fish that was born in the river. It won't be a hatchery trout stocked in the reservoir and flushed through Island Park Dam. That may not matter to you, but it does to me.

Mike Lawson is former owner of the Henry's Fork Angler. His book Fly Fishing the Henry's Fork (Greycliff Publishing Company) was publishined in 2000. He lives in St. Anthony, Idaho.

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