The Henry's Fork

by Mike Lawson

The Henry's Fork is a tributary of the Snake River. It has been called the largest spring creek in the world and is one of the most famous trout rivers in America. It is a very diverse river with plenty of public water that is easily accessed. It has a wide variety of water types from deep canyons to wide open meadows. There are several dams on the river with rich tail waters below. The spring creek sections of the river provide some of the greatest variety of insect hatches of any river in the world. The Henry's Fork is like several different rivers in one.

Upper Section

The river originates from two sources, Henry's Lake and Big Springs. Henry's Lake is a natural lake which has been dammed to increase its volume for irrigation of potato farms downstream. The lake itself is a world class trout fishery. The other source of the Henry's Fork comes from a giant spring known as Big Springs which provides more than 150 cubic feet of clear, cold water to the river. The section from the source down to the Coffee Pot Rapids above Island Park Reservoir is smooth, classic spring creek water which can provide excellent dry fly fishing for small trout.

The Henry's Lake Outlet was once an outstanding trout fishery. This stream has suffered from poor grazing practices and inadequate stream flows and is no longer a first rate trout stream. It meanders through a wide meadow for about 10 miles before it joins the other fork of the river which comes from Big Springs. Most of the Henry's Lake Outlet flows through private cattle ranches and permission must be obtained from the land owners in order to walk through their land to fish this stretch. Access can also be gained to walk up or down the stream from the U. S. Highway 20 bridge. There is another bridge which provides access to the lower part of the outlet from the Big Springs Road.

The Henry's Fork is closed to fishing from Big Springs to the confluence with Henry's Lake Outlet which provides a sanctuary for the trout. Big Springs is a popular tourist attraction where trout as large as ten pounds can be viewed from a bridge which crosses the river just below the springs. This part of the river flows through national forest land. Access can be gained from the Big Springs Road which follows the river upstream from Mack's Inn.

The Henry's Fork is not managed as a wild trout fishery from its source downstream to the Island Park Reservoir. This area is stocked heavily with hatchery trout. Fishing regulations allow for bait fishing and a liberal limit of six trout of any size. Because the fishing regulations are so liberal, trout over 12 inches are uncommon.

From the confluence at the Henry's lake Outlet to the U. S. Highway 20 bridge at Mack's Inn, the river provides very good fishing for small rainbows and brook trout. Most of the rainbows are hatchery stocked and very easy to catch. Specific imitations which match the mayfly and caddis hatches are usually not needed. When heavy mayfly hatches occur, such as the green drake in late June, larger trout can be taken with specific imitations.

The Upper Coffee Pot Campground provides access to the river downstream from the highway bridge at Mack's Inn. This is a very popular campground and is an excellent place to camp. Walking a 1/4 mile or so down the trail from the campground provides the best fishing. The water is very slow moving until it hits the Coffee Pot Rapids, about one mile below the campground.

The river narrows and speeds up through the Coffee Pot Rapids. There are many deep pools as the water cascades over large boulders. This area is very difficult to wade. The best fishing is with large nymphs and streamers. The best dry fly fishing is during the salmon fly hatch in early June. The trout in this area are small but large rainbows start moving up from the reservoir in September.

Box Canyon

The Island Park Reservoir stores a large volume of water which is used for downstream irrigation. The reservoir is fed by several small streams and springs in addition to the Henry's Fork. The reservoir provides excellent fly fishing opportunities for large rainbow and cutthroat trout.

The Henry's Fork from the Island Park dam downstream to Riverside Campground is managed as a wild trout fishery. This is total catch and release fishing and only artificial flies and lures with single barbless hooks may be used. This is the section of the Henry's Fork which is best known and anglers come from all over the world to fish this stretch. The Box Canyon and Harriman State Park, formerly known as the Railroad Ranch are well known for the large rainbow trout which inhabit this part of the Henry's Fork.

The Box Canyon is a three mile stretch of the river which flows from Island Park Dam to Last Chance. You can access the Island Park Dam from a gravel road just north of Pond's Lodge on U. S. 20. It's about a two mile drive to the parking area just below the dam. There is a good public campground about one mile below the dam called Box Canyon Campground. The road to the campground is just south of Pond's Lodge on highway 20. This road continues south past the campground to Last Chance. There are two fishing access roads about a mile south of Box Canyon Campground.

The water flows over a lava rock bottom through the Box Canyon. The water is very fast and wading is difficult even though most of the water is less than four feet in depth. This section of the river is extremely fertile with a good population stonefly nymphs, caddis larva, mayfly nymphs, leeches, crayfish, sculpins and other forage fish. The trout grow very rapidly and are in extremely good condition.
The salmon fly hatch normally occurs during the first week of June. Just prior to emergence the large nymphs crawl toward the back. The big rainbows move to the banks to feed on the migrating nymphs. Black rubber legs nymphs and black stonefly nymphs fished into the banks with a floating line can provide some of the best fishing of the entire season for rainbows up to 8 pounds.

After the salmon flies emerge they fly over the water to deposit their eggs. When the adult salmon flies are out the big trout can be anywhere. Large salmon fly dries in size 4 or 6 which float high and are easy to see in the fast currents are best. My favorite patterns include the Henry's Fork Salmon fly, Improved Sofa Pillow and Jug head. Rainbows over ten pounds have been caught during the salmon fly hatch in the Box Canyon. You must blind cast, covering as much of the good holding water as possible because it is hard to see the big trout when they rise to the naturals.

By mid June the salmon fly hatch is over in the Box Canyon. A smaller stonefly called the Golden Stone, starts to emerge at this time. These stoneflies aren't as concentrated as the larger salmon flies, but the continue to hatch until the middle part of July. The Henry's Fork Golden Stone, Improved Golden Stone, and Olive Stimulator in size 8 through 12 are my favorite patterns to imitate the golden stonefly hatch.
Even though there are good hatches of other stoneflies, caddis and mayflies, it is hard to catch large trout on dry flies after the salmon fly and golden stonefly hatches are over. There is so much food available, the bigger fish are reluctant to rise to the surface through the fast currents. While many anglers catch nice trout on attractor patterns, most of the bigger fish are caught on nymphs and streamers from mid July until the end of September when the stream flows are reduced.

The most popular nymphs for the Box Canyon are Black Rubber legs in size 6 - 10, #10 - #12 Prince Nymph, #10 - 12 Hare's Ear, #10 - 14 Pheasant Tail Bead Head, and #12 - 14 Olive Peeking Caddis. The most productive method for fishing these nymphs is with a foam indicator attached about six feet up a nine foot leader. Heavier 2X - 3X tippets are recommended because of the rocky bottom and are necessary to land very large, strong trout. I recommend a nine foot rod capable of throwing a six or seven weight line for nymph fishing.

Streamer fishing is also very productive in the Box Canyon. Olive and black woolhead scuplins in sizes 4 and 6 have produced trout up to 12 pounds. Other streamers recommended include Olive Zonkers, Silver Zonkers, Muddler, Black Flasha-bugger, and Olive Flasha-bugger is sizes 4 and 6. A floating line is usually sufficient for streamer fishing. Some anglers prefer to use a sink-tip line to get the fly deeper. An eight weight rod is best suited for fishing these big streamers in fast water.

Because the water is fast, it is very difficult to wade the river during the summer months. The stream flows are higher due to irrigation demand. Float fishing the river is most productive. By mid September the stream flows are reduced making the Box Canyon much easier to wade. With the decreased stream flows, the trout turn their attention to feeding on the surface. There are good hatches of Blue Winger Olive (baetis) mayflies. These hatches continue until late October. These trout are usually not selective and exact dry fly imitations are not needed. A size 18 Olive Humpy or Parachute Adams is deadly when the trout are rising to these mayflies.

Harriman State Park

The river slows and widens below Box Canyon at Last Chance. Last Chance is a resort area with, several motels, grocery stores, restaurants and fly fishing outfitters. The river runs near the highway at Last Chance providing plenty of access for anglers who aren't able to walk long distances. The Henry's Fork is spring creek-like from Last Chance through the Harriman State Park and Pinehaven areas. This stretch of the river is prime dry fly water with exceptional hatches of mayflies and caddisflies.

The Harriman State Park encompasses about six miles of the finest dry fly water in the world. The river is wide and flat. The trout are scattered throughout and all of this water has good numbers of large trout. The average depth is less than three feet deep making wading possible throughout. The upper Harriman flows from Last Chance to the Osborne Bridge on U. S. Highway 20 and the Harriman East continues from highway 20 to the summer area of Pinehaven. Public access is provided to this area at several locations. There is a large parking lot at the north boundary at Last Chance with rest rooms and drinking water. The first mile gets the most fishing pressure. I like to walk down the trail to the first big bend and fish down from there to get away from the crowds.

There is a walk in access at the mail box about a mile and a half down U. S. 20 from Last Chance. There is a parking area on the west side of the highway. Walk-in access is provided down a gravel road to the west. The walk is exactly one mile to the middle bridge across the river. The fishing is best upstream from the bridge. This section of the river is known as bonefish flats because the river is so wide and flat. Not only are the trout very selective in this area but the trout tend to cruise about making it very difficult to get a cast over them.

Access is provided to the lower portion of the Harriman Park from the main parking lot at the visitors center. Follow the signs from the Green Canyon Road which is just south of the Osborne Bridge. The main parking lot provides access to the famous. There is other great water upstream or downstream from the parking lot. Some of the water is deep in this area making it impossible to wade across the river in some areas.

Below the Osborne Bridge the Henry's Fork flows through the Harriman East property. This land is also owned by the state of Idaho and managed as a wildlife sanctuary. The water is slow and smooth but there is a deep channel which makes it impossible to wade across the river. You can walk down from the Osborne Bridge. There are plenty of trout on both sides of the river but the wading is best on the south side of the river.

Another access is provided to this area from the Mesa Falls Scenic Highway at Wood Road #16. This road is a very primitive road and four wheel drive is highly recommended. The road can be impassible during wet weather. It's about a two mile drive to the river. There is good spring creek type water for at least a mile above and below.

Spring creek equipment is recommended for this section of the river. I like rods from 8 to 9 feet long with a size 3 or 4 weight line. Leaders at least 12 feet tapered to 5X or 6X are recommended.
There are good numbers of mayflies and caddis which emerge in this section from opening day, on June 15 each year, to the end of October. June provides the most intense mayfly and caddis activity. The Pale Morning Dun (Ephemerella inermis) start hatching in early June and continue until the middle of August. The duns start hatching in mid morning. The spinners fall earlier in the morning and at dusk. Flies should be tied in size 16 and 18. PMD No-hackle, PMD Thorax, and PMD Sparkle Dun work best when the duns are on the water. Emergers and cripples also work very well during this hatch. PMD Half Back Emerger, PMD Cripple and PMD Floating Nymph frequently work on those ultra selective fish that won't take a dun. The female spinner of the Pale Morning Dun is pale yellow, almost the same color of the dun. The males are rusty brown. Both work well when the spinners are on the water.

The Green Drakes (Drunella Grandis) and Brown Drakes (Ephemera Simulans) start to emerge during the third week of June. The Green Drakes hatch best in the stretches of the Harriman Park which have a coarse gravel bottom. From the mouth of Box Canyon down to bonefish flats and the faster water below the middle bridge are excellent areas to fish the Green Drakes. They start to emerge during late mornings. Best Green Drake activity occurs during cool, cloudy weather when they hatch throughout the day. Green Drake patterns should be tied in size 12 or 10. Emergers are very effective. The Green Paradrake is my top choice when the fish are taking the duns. The spinners fall early in the morning and is usually very sporadic. A size 12 Rusty Spinner works well when the spinners are on the water.
Brown Drakes emerge in slow water which has a fine gravel or silty bottom. They start hatching about 7:00 PM and continue until dark. The spinners fall about an hour after the duns. Some trout will key on the nymphs which swim to the surface. Brown Drake Nymphs should be tied in size 8 or 10. Brown Drake Emergers also work well when fished just under the surface film. Mike's Brown Drake is a very effective pattern when the trout are feeding on duns. Brown Paradrakes are also effective. Brown Drake Partridge Spinners work best late in the evening just as the sun goes down.

Caddis hatches during the evening hours in June can be very prolific. I have spent many evenings watching dozens of large rising at Last Chance trying to determine whether they were feeding on caddis or PMD spinners. There are two important types of caddis which emerge in June and early July. The larger species is best imitated with a size 14 or 16 Hemingway Caddis. Olive Emergent Sparkle Pupa is also very effective. There is also a small caddis which can be matched with a size 20 Spent Partridge Caddis.

The Small Green Drake (Drunella flavilenea) is the most important mayfly hatch during July. These beautiful mayflies emerge during the late afternoon hours from Last Chance through the Harriman Park. Like the its larger cousin, the Green Drake, these mayflies hatch best when the weather is cloudy and cool. No-hackles, Sparkle Duns, and Thorax tied with a dark grey wing and an olive brown body are great imitations of the duns. Flav patterns should be tied on size 14 hooks. Emergers are also very effective. The spinners have a dark brown body and fall at dusk.

The Speckled Spinner (Callibaetis nigritis) start hatching in July and continue until the end of September. Normally a lake species, this mayfly is common in the sections of the Harriman Park which support lots of aquatic vegetation. The duns are emerge very sporadically and are not usually important. The spinners can be present in very large numbers. My favorite pattern is a size 16 cream spinner tied with spent grey partridge wings.

Tricos (Tricorythodes minutus) start emerging in early August and continue throughout September. The duns start coming off at dawn. The spinners hit the water about 8:00 AM. Patterns should be tied in size 20 or 22. No-hackles and Thorax patterns work when the duns are on the water. I have had my best success with a White / Black Hen Spinner when the Tricos are on the water.

Caddis hatches taper of from mid July through early August. During late August there is another caddis hatch which provides outstanding dry fly fishing. These caddis have a dark grey wing and olive body and hatch late in the evening and early in the morning. There are two species. Best patterns are a size 12 - 14 Hemingway Caddis and size 14 or 16 Spent Partridge Caddis and E-Z Caddis. The E-Z Caddis is similar to a Spent Partridge Caddis but is tied with a parachute post for better visibility.
By early September the temperatures cool down and the caddis hatches are over. Two very important mayflies start to emerge, however. The Mahogany Dun (Paraleptophlebia) hatches in the mid morning hours and is the most important September insect hatch. A size 16 Pheasant Tail Flashback Nymph is effective when fished just prior to the hatch. As with most other mayflies, I like No-hackles, Thorax and Sparkle Duns to match this hatch. The patterns should be tied on size 16 or 18 hooks with a dark grey wing and dark tan body.

Blue Winged Olives (Baetis tricaudatus) in size 20 - 22 also produce excellent fishing in the Harriman Park. Floating nymphs and emergers are productive as well as No-Hackles and Thorax patterns. Flies should be tied with a light grey wing and grey-olive body.

Terrestrials are also important throughout the season in the Harriman Park section of the Henry's Fork. If I could only take one fly with me anytime of the season it would be a black beetle. Some of the most exciting fishing I've ever experienced was during windy August afternoons when hoppers were blowing into the water. The fish really smash these large insects. The Henry's Fork Hopper is size 10 and 12 is by far the best hopper pattern for the Harriman Park section of the Henry's Fork.

Large numbers of flying ants are common during August and early September. These insects can swarm onto the water creating a frenzy of feeding activity. This king of ant activity is very unpredictable but anglers should be prepared with plenty of Black Flying Ants in sizes 16 through 20 and large Brown Flying Ants in sizes 14 and 16.

Wild Canyons

Below the Harriman East section of the park the Henry's Fork picks up velocity as it flows southward toward the town of Ashton. It drops almost 1000 feet in elevation over the next 15 miles. Much of this part of the river is difficult to reach, requiring a long climb down into a deep canyon. This section of the river is managed as a wild trout fishery. There are no hatchery stocked trout and the limit is two fish with a slot of no fish between 8 and 16 inches from Riverside Campground to St. Anthony.

There are several access points which provide anglers a place to get to the river and walk from there. Riverside Campground is located just east of U. S. Highway 20, about 5 miles south of the Osborne Bridge. This is my favorite campground on the Henry's Fork. The water is very swift and wading is difficult if not impossible.

The only other access from Highway 20 is the Sheep Falls Trail located about 5 miles south of Riverside. Take the Sheep Falls Road and look for the Sheep Falls Trail sign. Sheep Falls is about a half mile walk from the end of the road.

The best access points to the canyon section of the Henry's Fork is from the Mesa Falls Scenic Road. There are several roads which are well marked to access the river. Hatchery Ford is located about ten miles south of the junction with U. S. 20. This gravel road goes down into the canyon right to the water. You can walk up or downstream from here. There are also some primitive camping sites and a boat ramp at this location. Float fishing is excellent from Riverside to Hatchery Ford but the river cannot be floated further downstream because of several water falls.

Upper Mesa Falls provides a breath taking view of the Henry's Fork canyon. This falls is over 100 feet high and is worth taking a look at even if you don't fish. There is good fishing upstream from the falls. The water is very fast and wading is impossible in some areas.

The Henry's Fork flows out of the deep canyon just above the confluence with Warm River. From Warm River to the Ashton Reservoir the river takes on a much difference character. This water has a good definition of riffles, glides, runs, and pools. There are some very large Brown Trout in this stretch in addition to a good population of rainbows mixed with a few Cutthroat and Brook Trout.

This section provides excellent float fishing during the salmon fly hatch in June. The dry fly fishing slows down after the Pale Morning Duns quit hatching in early August. Float fishing is popular throughout the summer with attractor dry flies and nymphs. Rubberlegs, Prince Nymphs, Bead Head Nymphs and Caddis Larva are best when fished with a small indicator.

Access is good throughout most of this stretch. The Henry's Fork road follows the river downstream to the U. S. Highway 20 bridge above Ashton. This gravel road turns west just after the highway crosses Robinson Creek. The road follows the river for about three miles, climbs to the canyon rim and then drops back down to the river. This section of the Henry's Fork is a great place for an inexperienced fly fisher to catch some wild trout.

Ashton Tail water

The most productive stretch of the Henry's Fork lies between the Ashton Dam and the confluence of Fall River, a distance of about five miles. The Ashton Reservoir creates a tail water fishery which produces exceptional insect hatches and a fantastic trout population. The rainbows and browns are in excellent condition with small heads and robust bodies. These trout average about fifteen inches in length with good numbers in the 18 - 20 inch range.

The Ora Bridge crosses the river just below the Ashton Dam. This access can be reached from the county road directly west of Ashton. There are several motels, restaurants and grocery stores in Ashton. The drug store on main street has an old fashioned fountain which makes the best milk shake in the state of Idaho. It makes a great treat after a long day of fishing.

The county road follows the river down from the Ora Bridge and crosses the river two miles downstream at the Vernon Bridge. There is a gravel road which follows the river downstream on the north side of the bridge and another gravel road the goes upriver on the north side of the bridge. The county road joins back with U. S. Highway 20 at the small town of Chester. Four miles south of Chester another county road crosses the Henry's Fork again providing additional access to the Henry's Fork. The north exit to St. Anthony also crosses the river. This fishing is good from this bridge downstream, through the city park in St. Anthony. St. Anthony has plenty of accommodations for the visiting angler.
The river is spring creek-like with lots of weed beds and springs which seep from the stream bank. There are some deep runs but most of the water is shallow enough to wade without difficulty.

 Salmon flies emerge in late May providing exceptional early season angling. Pale Morning Duns, Green Drakes, and Flav mayflies hatch in significant numbers in June and early July. Another large mayfly, the Grey Drake (Siphlonorus occidentalis) hatches during this time. The spinners are the important stage of this mayfly as they mass to the stream in the late afternoon and fall on the water in the evening. My favorite pattern is a size 12 Adams. I have had some of the best dry fly fishing of my life during the Grey Drake spinner fall on this section of the Henry's Fork in late June.

Caddis flies are also very important with heavy hatches occurring in the evening hours during June and July. These trout aren't usually very selective and a size 14 Elk Hair Caddis or E-Z Caddis work very well. Another favorite pattern is a size 14 or 16 Renegade fished wet. Another good all around pattern is a size 16 Parachute Adams.

The fishing in this area slows down during the mid summer months with increased stream flows from heavy irrigation demand. After flows are reduced in mid September the dry fly fishing improves with good hatches of Blue Winged Olive and Mahogany Dun mayflies. The best dry fly fishing occurs during late September and early October with hundreds of rising trout.

The general fishing season closes on the Henry's Fork on November 30. The river is open to fishing year round from the Vernon Bridge downstream. Midge hatches provide good dry fly fishing most of the winter. There is also a very good Blue Winged Olive hatch in late March and early April. One of the best caddis fly hatches occurs from mid April to early June.

The Henry's Fork has received a lot of publicity over the years as one of the premier trout rivers in the world. Most of this publicity has focused on the Harriman Park stretch, which encompasses only about seven miles. There are still more than 30 miles of great trout water that are relatively unknown. The Henry's Fork is truly one of the most remarkable and unique trout rivers in the world.