Southeastern Idaho Fly Fishing Guide

Quick Reference

What	When	Key Numbers
Henry's Fork	June 15 - Nov (Ranch opens June 15)	300-600 CFS Box Canyon; 700-900 CFS ideal
South Fork Snake	Year-round (salmonflies late June)	5,000+ trout/mile; 900-1,200 CFS winter wade
Teton River	Memorial Day - Nov 30	Native Yellowstone cutthroat; giant stoneflies early June
Guided trips	Book ahead for June hatches	Three Rivers Ranch, South Fork Lodge
Fly shop	Henry's Fork Anglers	(208) 558-7525, Last Chance

Overview

Southeastern Idaho holds some of the finest trout water in North America. The Henry's Fork and South Fork of the Snake River draw anglers from around the world for their prolific hatches, wild trout populations, and mountain scenery. Add the Teton River's native Yellowstone cutthroat and the Portneuf's accessible brown trout fishing, and you have water that can occupy a lifetime.

The area sits at the headwaters of the Snake River drainage, with the Teton Range to the east and Yellowstone's high plateau to the north. Spring-fed sources keep many waters cool through summer—water temps typically run mid-50s to low 60s°F in upper stretches—supporting diverse insect populations and healthy trout.

Seasons and Conditions

Spring (April-May)

Rivers run high and off-color from snowmelt. The South Fork, as a tailwater below Palisades Dam, remains fishable when freestone rivers blow out. Focus on nymphing and streamers. Water temps are cold (often 40s°F), so slow your presentations and fish midday warmth.

Early Summer (June)

The magic window. Salmonfly hatches start late May on lower sections and progress upstream through June—those 2-3 inch stoneflies bring every fish in the river to the surface. The Henry's Fork sees its famous green drake and brown drake hatches starting mid-June. Pale Morning Duns emerge across all rivers. This is prime time, but expect company—Harriman Ranch's June 15 opener draws anglers from across the country.

Peak Summer (July-August)

Outstanding dry fly fishing continues with PMDs, caddis, yellow sallies, and terrestrials. Hoppers, ants, and beetles become effective along grassy banks from July through September. Water temps in the mid-50s to low 60s are ideal; above 68°F, fish mornings and evenings. The South Fork runs high (8,000-12,000 CFS) for irrigation—fish foam lines and edges.

Fall (September-October)

Cooling temps trigger renewed hatches and aggressive fish. Blue-winged olives return in force. Brown trout become territorial as spawn approaches—streamer fishing excels. The South Fork drops to 2,000-4,000 CFS by mid-September, opening excellent wade fishing. Crowds thin considerably.

Winter (November-March)

Fishing slows but doesn't stop on tailwaters. The South Fork runs 900-1,200 CFS with water temps dipping to 38°F. Midge hatches occur on warm afternoons. Target 11am-3pm and expect slow, methodical fishing. Wade access opens up significantly at these flows.

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Henry's Fork of the Snake River

The Henry's Fork is arguably the most celebrated dry fly stream in the lower 48—Trout Unlimited once ranked it the top trout stream in the country. The river originates at Big Springs near Yellowstone, producing 120 million gallons of cold, clear water daily.

Box Canyon

Length: 3-3.5 miles from Island Park Dam to Last Chance

This narrow, boulder-strewn canyon offers fast pocket water. The canyon ranges from 100 feet wide at its widest to about 50 feet at its narrowest, lined with pines and littered with rocks.

Flow guidance:

• Below 600 CFS: Excellent wade fishing; work between boulders carefully
• 700-900 CFS: Good overall conditions; wading still manageable
• Above 1,200 CFS: Fish from a boat—wading becomes difficult and dangerous

Techniques: Nymphing dominates here. Pat's Rubber Legs (#6-8), stonefly patterns, and attractor nymphs produce. At lower flows (around 780 CFS), mornings favor nymphs while evenings can produce streamer action.

Access: Gravel road just north of Pond's Lodge on US-20 leads to parking below the dam—about 2 miles. A hiking trail runs the canyon's length with multiple access points from Old Highway 191.

Harriman Ranch (Railroad Ranch)

Length: 6-7 miles through Harriman State Park

This meadow section is what made the Henry's Fork famous. The river slows into a wide, high-country meadow with views of the Centennial Mountains and Tetons. Large rainbow trout feed selectively in crystal-clear water on complex hatches.

The reality check: Experienced anglers argue this offers the most challenging light tackle fly fishing on the planet. The slow, clear water allows trout to inspect every offering. These fish are educated daily by skilled anglers. Many fish here for years before consistently hooking up. If it's your first trip, consider hiring a guide—the knowledge about current hatches and approach is invaluable.

Regulations: Catch-and-release only, fly fishing only, barbless hooks required. Season runs June 15 through November 30. Closed December 1 through June 14.

Timing and pressure: June 15 opener and the following week are extremely busy. The salmonfly hatch and Ranch opener draw anglers from surrounding states and countries. For solitude, fish late July through early fall or early spring before the opener. The Ranch fishes best just before dark—plan to stay late.

What to bring: Small flies rule. Sizes 16-22 are common. Match the hatch precisely. Stop at Henry's Fork Anglers in Last Chance to find out what's hatching.

Lower River

Below Ashton Reservoir, the Henry's Fork takes on freestone character, flowing through agricultural land. Rainbow and brown trout populations are healthy, and fishing pressure is much lower than upstream sections. Easier wading access makes this a good place to build confidence before tackling the Ranch.

Henry's Fork Hatch Calendar

Month	Major Hatches	Notes
June	Salmonflies, Golden Stones, Green Drakes, Brown Drakes, PMDs	Green drake hatch lasts 10-14 days, starts around 11am
July	PMDs, Caddis, Yellow Sallies, Green Drakes (late)	Golden stones follow salmonflies
August	Tricos, Terrestrials (hoppers, ants, beetles), Caddis	Fish mornings for tricos, terrestrials when wind is calm
September-October	BWOs, Mahogany Duns, Tricos	Renewed hatches with cooling temps

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South Fork of the Snake River

Often called the best cutthroat stream in the West, the South Fork flows 66 miles from Palisades Dam to its confluence with the Henry's Fork. This tailwater supports over 5,000 trout per mile—wild Yellowstone and Snake River fine-spotted cutthroat, plus rainbow and brown trout ranging from 15 to 25 inches.

Understanding South Fork Flows

The South Fork is a tailwater controlled by irrigation demand. Flows change based on downstream agricultural needs (potatoes and sugar beets). Watch for rapid changes and avoid being caught on exposed gravel bars when releases increase.

Flow Range	Conditions	Best Approach
900-1,200 CFS	Winter flows; excellent wade access	Walk gravel bars, sight-nymph
1,500-1,800 CFS	Upper sections; technical water	Wade inside bends, dry-dropper rigs
4,000-8,000 CFS	Transitional; dropping from summer peaks	Drift boat fishing, streamers and nymphs
8,000-12,000 CFS	Peak summer irrigation flows	Fish foam lines, edges, and banks from drift boat
Above 12,000 CFS	High water	Focus on slowest water, streamers tight to banks

Water temps: Summer runs mid-50s to mid-60s°F in upper stretches. The tailwater stays cool even when air temps spike. Winter can dip to 38°F—dress appropriately.

Float Sections

Section	Put-in	Take-out	Miles	Float Time	Character
Upper	Palisades Dam (Husky)	Conant	12	6-8 hours	Swift water, tree-lined banks, Falls Creek Falls, best canyon scenery
Upper Short	Husky	Spring Creek	5	4-5 hours	Half-day option
Canyon	Conant	Cottonwood	14	Full day	Volcanic cliffs, cottonwood forest, largest bald eagle winter roost in Northern Rockies
Canyon Overnight	Conant	Byington	25	2 days	16 designated campsites; popular overnight trip
Lower Canyon	Cottonwood	Byington	12	Full day	High cliffs, Henry's Bathtub, Table Rock; requires early start
Heise	Byington	Lorenzo	7	4-5 hours	"Brown town"—big browns, Twin Bridges section excels during salmonfly hatch
Lower	Lorenzo	Menan	8	5-6 hours	Amazon-like vegetation, dead tree piles, early salmonfly hatches, trophy browns

Logistics note: Cottonwood (Fulmer) boat launch requires a long dirt road drive on the north side of the river—plan 45+ minutes on rough road to reach Highway 26 via Heise.

Wade Fishing Access

While the South Fork is primarily a drift boat fishery, wade fishing is productive if you know where to go:

• Swan Valley Bridge: Easy access on Highway 26 or Snake River Road between the bridge and Fall Creek Falls. Best at winter flows (900-1,200 CFS).
• Conant area: Gravel bars around the access point; walk upstream or downstream.
• Byington flats: Wide gravel bars downstream of the ramp; best at lower flows.

Parking fees: BLM requires day or season pass at boat access sites (Fulmer, Byington, etc.) from May 24 through September 30. Day pass is $3.

South Fork Hatch Calendar

Timing	Hatch	Patterns
May	Pre-runoff nymphing	Cheater Belly Stonefly Nymph (#2-8), Pat's Rubber Legs (#6-8)
Late June-Early July	Salmonfly (4 weeks)	Orange Water Walker (#4-8), Joe's Stone (#4), Salmonfly (#6)
July	Golden Stones	J-Slam Golden Stone (#4-10), Black Gold Stimulator (#6)
July-August	PMDs, Caddis, Hoppers	Pink Sparkle Dun (#16-20), Schroeder's Parachute Hopper (#8-10), Lightning Bug (#12-18)
Late August	Mutant Stones	Small stubby-winged stones; skitter flies early morning
September-October	BWOs, Streamers	Tungsten Split Case BWO (#18-20), Sex Dungeon (#2-4) for fall browns

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Teton River

The Teton River is one of the last strongholds for Yellowstone cutthroat trout. This 81-mile tributary of the Henry's Fork flows through Teton Valley, fed by springs that maintain near-constant water temperatures in upper sections.

Upper Teton

Slow meadow water with beautiful seams and eddies. Ideal dry fly territory for native cutthroat that rise aggressively to well-presented flies. Less pressure than Henry's Fork and South Fork—an attractive alternative during peak season.

Lower Teton Canyon

Faster pocket water with deeper pools holding some of the river's largest trout. More technical wading conditions.

Access Points

• Cache Bridge: 15 minutes north of Victor off Highway 33. Take W 4000 North.
• Bates Bridge to Big Eddy: Most popular section; expect some company during peak season.
• Harrop Bridge and below: Giant stoneflies in early June.

Teton River Hatches

• Early June: Giant stoneflies below Harrop Bridge (up to 3 inches)
• Mid-June through fall: PMDs, Caddis
• July through fall: Baetis, Mahogany Duns, Rusty Spinners
• Late July-September: Hoppers
• September: Grey Drakes (large mayflies, 1-1.5 inches)

Regulations: Memorial Day weekend through November 30, trout limit is 6 with no harvest of cutthroat trout. Catch and release encouraged for all cutthroat.

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Portneuf River

For anglers based in Pocatello or seeking less-traveled water, the Portneuf offers solid brown trout fishing with easier access.

Below Lava Hot Springs

The lower river meanders through valley farmland with good populations of brown trout. Fish deeper holes, runs, undercut banks, and shaded areas under overhanging trees. A 5 or 6 weight rod with floating line works well. The high banks offer good visibility—and make stealth critical. It's easy to cast shadows and spook fish.

Above Lava Hot Springs

Upper reaches hold rainbow and Yellowstone cutthroat, plus occasional brook trout. The Kelly-Toponce area has beaver ponds with small wild fish—good for prospecting with attractor dries.

Techniques

Hopper-dropper rigs excel in summer. Woolly worms and San Juan worms (#10-16) produce year-round. Move around and seek active fish rather than camping in one spot.

Regulations

Above East Main Street Bridge in Lava Hot Springs: catch-and-release only December through Memorial Day weekend, no bait, barbless hooks required. Standard 6-trout limits the rest of the year, but cutthroat harvest is always prohibited. Parts through Fort Hall Reservation fall under tribal jurisdiction—separate permit required.

Note: A portion through Lava Hot Springs town is closed year-round (swimming and tubing area).

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Beginner-Friendly Options

South Fork of the Snake: Consistent flows and abundant fish make it forgiving. Guided drift boat trips let beginners cover productive water while learning. Summer dry fly action provides plenty of practice opportunities. The sheer number of fish (5,000+ per mile) means more chances to connect.

Lower Henry's Fork: Below Ashton, easier wading access and less technical fish than Harriman Ranch. Build confidence here first.

Portneuf River: Accessible from Pocatello with less pressure. Brown trout aren't as selective as Henry's Fork rainbows—a good training ground without the technical demands.

Technical Water

Harriman Ranch: The pinnacle of dry fly difficulty. Flat, clear water. Fish that inspect every offering. Many anglers fish here for years before consistently catching fish. Come prepared with a full range of sizes in each pattern (often #16-22), long fine tippets (6X-7X), and patience. The Ranch fishes best at dusk.

Box Canyon: Fast pocket water requiring skilled nymphing. Slick boulders and strong current make wading challenging, especially above 1,000 CFS.

Upper Teton Canyon: Limited access and technical conditions for experienced waders seeking solitude.

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Local Fly Patterns

Henry's Fork Essentials

• Lawson's Green Drake (#10-12)—Mike Lawson's pattern, developed for this river
• Green Drake Cripple (#10-12)—for picky risers
• Lawson's Green Drake Emerger (#10-12)
• Harrop's Hairwing Dun (PMD, #16-18)
• CDC Biot Comparadun (various colors, #16-20)
• Sparkle Dun (PMD, Callibaetis, #14-18)
• X-Caddis (#14-18)
• Parachute Trico (#20-22)

South Fork Essentials

• Orange Water Walker (#4-8)—local favorite for salmonflies, twitch through flats
• Cheater Belly Stonefly Nymph (#2-8)—all spring until salmonflies
• J-Slam Golden Stone (#4-10)—guide favorite
• Schroeder's Parachute Hopper (#8-10)—fish hard to the bank
• Pink Sparkle Dun (#16-20)—PMD imitation
• Pink CDC Biot Dun (#16-20)—dropper behind the Sparkle Dun
• Psycho May Nymph (#14-18)—covers almost all mayfly nymphs
• Sex Dungeon (#2-4)—fall browns

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Local Fly Shops

Call ahead for current conditions—these folks fish these waters daily and know what's working.

Henry's Fork Area

Henry's Fork Anglers (Last Chance)

• Phone: (208) 558-7525
• Address: 3340 Hwy 20, Island Park, ID 83429
• Hours: 7am-7pm daily (Memorial Day-Fall); 9am-5pm Mon-Sat (Winter)
• Established 1976; Mike Lawson's shop

TroutHunter (Island Park)

• Phone: (208) 558-9900
• Address: 3327 N. Hwy 20, Island Park, ID 83429
• Full-service shop with restaurant and lodging

South Fork / Teton Valley Area

TRR Outfitters - Driggs

• Phone: (208) 354-1200
• Address: 76 N. Main Street #101, Driggs, ID 83422
• Licensed on Henry's Fork, South Fork, and Teton River

WorldCast Anglers (Victor)

• Downtown Victor, ID
• One of few outfitters licensed on the Teton River

Jimmy's All Season Angler (Idaho Falls)

• Phone: (208) 524-7160
• Local knowledge, friendly staff

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Idaho Fishing Regulations

Idaho requires a fishing license for anyone 14 or older. Children under 14 fish free, though non-resident children's catch counts toward an accompanying adult's limit unless they purchase their own license.

Key points for southeastern Idaho (2025-2027 regulations):

• Standard Upper Snake Region limit: 6 trout (all species combined)
• Special rules vary by section—always check current regs
• Live bait (fish, leeches, frogs, salamanders) prohibited
• Barbless hooks required on catch-and-release waters
• Chumming illegal statewide

Harriman Ranch special regs: Catch-and-release only, fly fishing only, barbless hooks. Open June 15-November 30 only.

Purchase licenses at Idaho Fish and Game, license vendors, regional offices, or by phone at (800) 554-8685.

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Float Options

The South Fork is primarily floated by drift boat or raft. The 66-mile stretch from Palisades Dam is Class II water—no significant rapids, but current, sweepers, and obstacles require attention. Most anglers book with outfitters or lodges that provide boats and experienced guides.

Self-guided float logistics:

• Shuttle services available through local fly shops
• BLM parking fee required at boat launches (May 24-Sept 30)
• 16 designated campsites in the canyon section for overnight trips
• No camping in day-use parking lots (Byington, etc.)
• Kelly Island Campground (BLM) across from Byington for overnight stays

For whitewater elsewhere in Idaho, the state claims more navigable whitewater miles than any other in the lower 48—Middle Fork Salmon, Selway, and Hells Canyon of the Snake.

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Safety Considerations

• Cold water: Tailwaters run cold year-round (38-55°F). Waders, studded boots, and a wading staff reduce hypothermia risk from falls.
• Rapid flow changes: The South Fork can change quickly from dam releases. Watch for rising water and don't get caught on gravel bars mid-river.
• Spring runoff: May and early June bring high, fast, discolored water on freestone rivers. Check South Fork Snake River flows at Heise before planning.
• Afternoon thunderstorms: Summer storms develop quickly. Watch the sky and know your exit routes.
• Wildlife: Bears, moose, and other wildlife are common. Store food properly and make noise on trails.

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Getting There and Lodging

Airports:

• Idaho Falls (IDA): 45 minutes to South Fork, 90 minutes to Island Park
• Jackson Hole (JAC): 60 minutes to South Fork Lodge
• Salt Lake City: ~4 hours south

Fly Fishing Lodges:

Three Rivers Ranch (Warm River)

• Historic Orvis-endorsed lodge (first in 1974), Orvis Lodge of the Year
• Open May through November; day trips year-round
• Licensed on 16+ rivers including Henry's Fork, South Fork, Teton
• Phone: (208) 652-3750

South Fork Lodge (Swan Valley)

• On the South Fork; built 1998 by Mark Rockefeller
• Full-service fly shop, drift boat access to all sections
• 60 minutes from Jackson Hole

The Lodge at Palisades Creek (Irwin)

• Orvis-endorsed; open May-October
• Guided trips year-round on five South Fork sections (55 miles)
• Phone: (866) 393-1613
• 20 minutes from Idaho Falls Airport (Lorenzo take-out)

Henry's Fork Lodge (Island Park)

• Located near Harriman Ranch
• Focused on Henry's Fork and surrounding waters

Teton Valley Lodge (Driggs)

• Oldest continuously operating fly fishing lodge west of the Mississippi (since 1919)
• Access to South Fork, Henry's Fork, and Teton River

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Conservation

The Henry's Fork Foundation has worked since 1984 to conserve the Henry's Fork watershed—3,200 square miles spanning eastern Idaho and western Wyoming. Their science-based efforts include:

• 100+ research and monitoring projects completed
• Miles of riparian fencing to protect streambanks
• Water conservation programs (Precision Water Management, Farms and Fish)
• Real-time water quality monitoring (temperature, turbidity, dissolved oxygen)
• Collaboration with farmers to improve habitat while maintaining agricultural productivity

Support conservation by joining the foundation or practicing careful catch-and-release techniques. Handle fish minimally, keep them in the water, and use barbless hooks even where not required.

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Using RiverReports

Check current conditions before your trip:

• South Fork Snake River at Heise – Real-time flow data

South Fork flow interpretation:

• 900-1,200 CFS: Winter flows, excellent wade access on gravel bars
• 1,500-1,800 CFS: Upper sections; sight-nymph and dry-dropper
• 8,000-12,000 CFS: Summer irrigation flows; fish from drift boat, target edges and foam lines
• Dropping flows in September signal the transition to prime fall fishing

Henry's Fork flow interpretation:

• 300-600 CFS: Low flows; wade Box Canyon, technical Ranch fishing
• 700-900 CFS: Good overall conditions
• Above 1,200 CFS: Box Canyon best fished from boat; Ranch can be challenging

Compare historical data to understand typical seasonal patterns and identify windows when flows stabilize after runoff.