June Fishing on the Boulder River

June weather, stream flows, and summary

As Montana fly fishing rivers go, the Boulder River is one of the most beautiful rivers in the Treasure State. Along with its beauty, it is important to understand the myriad of factors that make fly fishing the Boulder River a unique Montana angling experience. The river is both easy and hard to fish—easy because it is home to plenty of 10 to 12-inch wild trout that are eager to eat well-presented dry flies, yet difficult to fish because floaters must be experienced on the oars and wading anglers must contend with lots of slippery boulders. 

Beginning high in the snowfields of the Beartooth Plateau near Yellowstone National Park, the Boulder River flows for nearly 80 miles to join the Yellowstone River outside of Big Timber. Halfway between Bozeman and Billings and about thirty minutes from Livingston, many anglers know of the Boulder River but few anglers actually experience the Boulder River in June—the river’s fast currents, sections of whitewater, and limited public access require most fishing in June to be from a boat. Because boat ramps at public access points are primitive, drift boats cannot be used, and with the river’s abundance of whitewater and technical rowing, only skilled boaters utilizing specially designed rafts should float and fish the Boulder River. 

The river is best described in two sections—the Upper and Lower—sections. The upper section above Natural Bridge is characterized by fast pocket water. Getting around this section by boat can be challenging unless you're an expert whitewater kayaker. Small, yet aggressive trout inhabit the Upper section and the Boulder Road parallels the river in much of this section and only on USDA Forest Service land is access available.  

The lower section begins downstream of Natural Bridge and is most often surrounded by hay pastures and cottonwoods. The river gets its name from this section because of the consistent riffles tumbling aggressively over boulders followed by short deep aquarium-like pools. On the bottom of many of these pools are large boulders. Almost 100% of the land bordering the lower Boulder is private property making access difficult. 

Because much of the upper section flows through the Custer-Gallatin National Forest, this section is the best option for walking-and-wading anglers as access is more available than the river below Natural Bridge. The river still contains large, slippery boulders but the public land at least allows anglers to get to the river. Below Natural Bridge access points are spaced-out and floating is the primary means of accessing the river. 

By early June snowpack data can paint a detailed picture to help forecast when the Boulder River may crest and begin to drop. Because the average annual peak streamflow occurs around June 20, by the second week of June the day-to-day forecast is the best gauge for when the river might come into form. When it does drop and clear enough to fish—typically below 2,000 cubic feet per second—the river is one of the best freestones in Montana. But, only very skilled boaters should attempt to float and fish the Boulder River in June. 

The Boulder River sees a diversity of weather patterns in June. Early June has an average daily high temperature hovering around 65 degrees F while later in the month average daily high temps tick close to 80 degrees F. Later in the month the prevalence of sunny days far out-weigh overcast days. Because the weather is varied in June, so is the river’s condition. If the first half of June is cold and rainy, snowmelt runoff is delayed, forcing anglers to wait until later in June for a fishable river. If the first half of June is warm and dry, snowmelt runoff may happen sooner, creating the possibility for the river to be in prime shape as early as June 20th. In most years the Boulder is fishable and floatable between June 20th and June 25th. 

When the Boulder River becomes clear enough to fish, hatches of salmonflies, Golden stoneflies, and Yellow Sally stoneflies occur. Golden stoneflies are an important hatch occurring shortly after salmonflies. Pale Morning Duns (PMDs) and various caddis species have strong emergence in June. With a diverse and abundant cornucopia of hatching insects, June fly fishing on the Boulder River can be consistent and action-packed—but only for very skilled and experienced boaters. 

June fishing: what to expect

In most years it is best to assume the Boulder River will not be fishable until the second or third weeks of June. There are exceptions—an unseasonably frigid and dry cold front moves in during early June or the winter’s mountain snowpack is well below annual averages. Assuming those two factors are at bay, by mid-June, the weather forecast and stream flows can provide enough insight to how the river will fish in the middle and later part of June.

Once the Boulder River drops below 2,000 cubic feet per second (cfs) floating anglers can realistically float and fish the river. However, these flows are still high and fast for fishing. The river’s stream flows typically run clear but because the Boulder River is primarily a pocket-water fishery, with flows above 1,500 cfs, boaters must be skilled to navigate the river’s many whitewater sections. Anglers must be quick on the cast and the hookset because many of the Boulder River’s opportunistic trout strike fast. 

This makes for exciting fishing—the many pockets of soft water next to fast water on the Boulder River often hold trout—and anglers can almost always fish dry fly and dropper rigs. A size 10 high-floating dry fly with a size 14 dropper is typically all that is needed on the Boulder River once the river drops below 1,500 cfs.  

By late June Pale Morning Duns and caddis may begin to hatch. Stream flows may still be high but clarity may have improved to more than two feet. Leaders can be lengthened to 9 foot 4X and single dry flies in appropriate sizes to match hatching PMDs or caddis can be fished. However, because the Boulder River’s currents are fast and strong, most anglers opt for a size 8 or 10 dry fly and smaller dropper nymph or second dry fly. 

Once the river comes into shape below 1,500 cfs, fishing on the Boulder River ranges from good to spectacular. The fish rarely see enough flies to become too educated and fishing large attractor dries through most of the day is the norm rather than the exception. Popular choices are Chubby Chernobyls in tan or gold and in sizes 8 through 12. For dropper nymphs beadhead Pheasant tails or Prince nymphs in sizes 12 through 16 work well. 

With pocket water and fast currents dominating the character of the Boulder River, fly and leader selection is straight-forward. Fly sizes for dries rarely drop below size 12 and for nymphs below 16. A 7.5 foot 2X leader is ideal for dry-dropper rigs, as the shorter stouter leader makes quick casts and mends easy. For fishing droppers, choose fluorocarbon because that sinks faster than monofilament, which is crucial in the rushing pocket water of the Boulder River. 

Where to find June trout on the Boulder

When the river’s streamflow drops by mid- or late-June, finding trout on the Boulder River is easy—trout hold and feed in typical fast-water/pocket-water lies. These are: in-front of and behind boulders or any other structure; along bank-side seams and soft currents near faster currents; drop-offs below shelfs; and around submerged structure in the many pools below a run of whitewater or large run of rapids. 

Finding trout on the Boulder River may seem obvious, but because the river is a fast-flowing, boulder-filled river with several sections of whitewater combined with stream flows and public access points few and far between, the biggest challenges to finding trout on the Boulder River are legally gaining access, safely floating the rivers rapids and rock gardens, and walking-and-wading the river. 

For the first few days of float- and fishable-friendly stream flows—typically below 2,000 cubic feet per second (cfs)—trout will be found near willows, submerged rocks and branches, and other structures picking off salmonfly and Golden stonefly nymphs and adults. Stoneflies hatch by clinging to structure and then emerging from an exoskeleton, trout follow the insects and become opportunistic feeders as the current washes away the structure-clinging nymphs. The fast and high flows of the first fishable window of stream flows cause trout to hang near structure and in slow water. Target eddy-lines, foam-lines created by eddies, and any slow water where a Boulder River trout can take refuge from the fast currents. 

As stream flows drop below 1,500 cfs and when Pale Morning Duns and caddis hatch, often in the later third of the month, stream flows are lower and trout can now hold in classic pocket water lies, riffles, deeper runs and pools, near mid-river shelfs, and even on shallow flats. On the Boulder River in June during a PMD or caddis emergence, trout can be found at the tail end of a shelf or riffle gorging themselves.

If stream flows drop below 1,000 cfs by the last week of June—in some years this can occur, and some years the river doesn’t drop below 1,000 cfs until July—Boulder River trout can be found in a variety of holding and feeding lies. From mid-river structure and boulders to seams along banks to drop offs and in deeper water, flows of below 1,000 cfs are favorable for finding plenty of hungry Boulder River trout. 

Important June hatches

Hatches on the Boulder River in June are strong. Knowledge of each individual hatch is important but not essential to success. Because the Boulder River’s flows are fast and fishing pressure is often lighter than other rivers, proper presentation of attractor dries and nymphs is often more important that matching the hatch. 

After snowmelt runoff peaks in mid- or late-June the Boulder River often drops and clears quickly. With these changes in flows, the variety of hatches can change daily. Because of this, the diversity of hatches on the Boulder River is part of the excitement of fishing this unique freestone. 

Salmonflies hatch on the Boulder River by mid- to late-June in most years. Although not a strong emergence, these are the first flies to hatch after runoff. After salmonflies hatch, Golden stoneflies, Yellow Sally stoneflies, Pale Morning Duns (PMDs) and caddis dominate. Once salmonflies and golden stoneflies are finished—typically by July 1—PMDs and caddis provide ample opportunities for dry fly fishing.

Caddis also hatch on the Boulder River in June. But because stoneflies dominate the hatches, most of the Boulder River’s opportunistic trout forego caddis and gobble-up well presented Golden stonefly patterns. 

Boulder River fly box for June

Stonefly nymphs in brown and black in sizes 8 through 10

Salmonfly dry flies in sizes 4 to 8

Golden stonefly dry flies in sizes 6 to 10

Yellow Sally stonefly dry flies in sizes 10 and 12

Caddis pupae in sizes 10 to 16

Caddis dry flies in sizes 10 to 16

Pale Morning Dun nymphs in sizes 12 to 16

Pale Morning Dun emergers in sizes 12 to 16

Pale Morning Dun dry flies in sizes 12 to 16

Sculpin patterns in sizes 2 to 6

Streamers in olive, black or brown in sizes 2 to 6