Fly Fishing Henry's Fork and Henry's Lake

Fly Fishing Henry's Fork and Henry's Lake: Plan Your 2027 Summer Getaway to Island Park, Idaho

Quick answer: On the Henry's Fork in summer, nymph Box Canyon or fish hoppers and afternoon PMDs on the Railroad Ranch. On Henry's Lake, go early with a sinking line and a leech, because trout sit deeper once the water warms. Island Park KOA Holiday is on Highway 20 near Henry's Lake, so both are easy day trips from camp.

The Henry's Fork comes out of the ground at Big Springs, cold and steady, and it stays that way all summer. That's the draw. In late summer, when a lot of Western rivers are running low and warm and the fish are sulking on the bottom, the upper Henry's Fork stays cold enough that trout keep feeding through the morning and bugs keep coming off in the afternoon. A few miles north sits Henry's Lake, where cutthroat-rainbow hybrids and brook trout can top 20 inches.

Camp at Island Park KOA Holiday and you can fish both in the same day.

Where to Fly Fish the Henry's Fork in Summer

Every few miles, the upper Henry's Fork turns into a different river. Pick your section by the fishing you want, not by what's closest.

Box Canyon

Fast, rocky, cold water right below Island Park Dam, with big rainbows that stay active all summer. Indicator nymph it with rubberlegs or perdigons. Wade carefully, or float it.

Railroad Ranch

Flat spring-creek water inside Harriman State Park. Hatches are sparse and the trout study your fly a long time before they turn it down, but you won't see many people. Fish hoppers and small PMD spinners on a long leader.

Warm River to Ashton

Lots of small and mid-size trout, with the odd big one. A dry-dropper or a streamer works. Go in the morning, before the boats show up.

The Ranch runs through Harriman State Park, and it humbles people. In late summer the PMDs come off in the afternoon in small numbers, a little heavier when it's cloudy, and when nothing's rising a hopper or a small black ant fished tight to the grass can still bring up a fish you'll be talking about at the campfire that night. Patience helps. If you'd rather bend a rod more often, go to Box Canyon.

Check a fly shop report before you head out. Flows out of Island Park Dam move around, and water temperature decides what's fishing well that week.

How to Fly Fish Henry's Lake in Late Summer

Henry's Lake covers about 6,000 acres and has a reputation for big trout. Midsummer is one of its tougher stretches. As the water warms, fish slide off toward the deeper weed beds, and the bite is best in the first couple of hours after sunrise, before the sun gets high and the fish settle in for the rest of the day.

Bring a type 2 or type 3 full-sinking line to get your fly down to them. Dark leech patterns, stripped slowly, are the standard here all summer. When fish push toward the weed edges or the cooler water near the springs, switch to a damselfly nymph or a scud.

You'll want a boat or float tube. Most of the shoreline is private, and Henry's Lake State Park on the south shore has a public launch.

And if your dates are flexible? October is the lake's other big season. That's when large cutthroat move toward the south shore.

Henry's Fork and Henry's Lake Fishing Rules

You need an Idaho fishing license to fish either water, and both have their own rules.

Henry's Lake is open year-round. From the Saturday of Memorial Day weekend through February 14 you can keep 2 trout, brook trout included, and once you have two you're done fishing. Staley Springs and the water within 100 yards of Hatchery Creek are closed.

To fish the Railroad Ranch, you'll drive into Harriman State Park, which charges $7 per vehicle unless you have an Idaho State Parks Passport.

Rules change. Look up your water on the Idaho Fish and Game Fishing Planner before you fish.

How to Plan a Fly Fishing Day from Island Park KOA

Plan the day around water temperature. Lake early, river midday, camp before it gets cold.

1. Get on Henry's Lake at first light. It's a few minutes from camp, and the early hours are your best shot at a big fish.
2. Head to Box Canyon by late morning, when the lake slows down. The cold water below the dam keeps the fishing steady.
3. Spend the afternoon on the Railroad Ranch, where the PMDs start showing up after lunch and a hopper slapped down tight to the grassy bank can pull up the kind of rainbow that makes the whole drive worth it.
4. Go back to your site, hang the waders, and fire up the grill.

Island Park KOA Holiday has RV sites up to 50 feet with 50-amp service, plus deluxe cabins with full baths for anyone who'd rather not sleep in a tent before a 5 a.m. start. There's a camp store and laundry on site. The dog gets a KampK9 park. The campground sits on Highway 20 about 10 miles from West Yellowstone, so anyone in your group who'd rather see Yellowstone and the rest of the area than stare at a strike indicator has an easy day trip.

Frequently Asked Questions

Is summer a good time to fly fish the Henry's Fork?

Yes, on the right water. Box Canyon and the canyon sections below it stay cool and fish well all summer. The Railroad Ranch is slower, with sparse afternoon hatches and good terrestrial fishing, but it gives up big trout to anglers who are willing to take their time and don't mind going an hour or more between shots at a rising fish. The lower river usually runs warm by late summer, so fish upstream.

What flies work on Henry's Lake in summer?

Brown and black leeches are the standard on Henry's Lake all summer. Damselfly nymphs and scuds work too, and so does a beadhead Prince fished like a scud. Once the water warms, fish them on a sinking line. The trout are deeper.

Do I need a boat to fish Henry's Lake?

Pretty much. Most of the shoreline is private, so a boat or float tube opens up far more water. Henry's Lake State Park on the south shore has a public launch.

How close is Island Park KOA to Henry's Lake?

A few minutes. Island Park KOA Holiday is on Highway 20 near the lake, about 10 miles from West Yellowstone and about 25 minutes from Yellowstone's West Entrance.

Plan your Island Park fishing trip. Summer weekends near Yellowstone fill up early. Reserve your site at Island Park KOA Holiday. Henry's Lake is a few minutes down the road.