July Fishing on the Stillwater River

July weather, stream flows, and summary

With its origin north of the high country of Yellowstone National Park and flowing from the Beartooth Plateau, the Stillwater River flows for nearly 70 miles to join the Yellowstone River about halfway between Billings and Bozeman. As if created specially for dry fly anglers who desire plenty of action, July on the Stillwater River is when this small river showcases its treasures. 

Home to abundant populations of wild rainbow and brown trout, native Yellowstone cutthroat trout and mountain whitefish, fly fishing the Stillwater River in July is a special experience for both floating anglers and walking-and-wading anglers. The backdrop of the snow capped peaks of the Beartooth Mountains provide the perfect complimentary image to this exciting freestone river between Billings and Bozeman. 

In most years, snowmelt runoff is complete by the first week of July and stream flows drop and clear more and more each day. If June receives above average precipitation or is colder than average, snowmelt runoff on the Stillwater River may continue through the first week of July, but those years are rare and by July 6th the Stillwater River is ideally suited for floating-and-fishing using a raft. Anglers fishing with experienced guides or oarsmen can enjoy the Stillwater River in early July but will find stream flows are very fast. Strong arms and quick casts are necessary in early July. 

By late July floating anglers can relax and enjoy the Stillwater River’s exhilarating riffles and runs without the risk of sweepers or dangerously high stream flows. Walking-and-wading anglers have more room to walk and cover water without risking trespassing, but they still need to be prepared to cover plenty of the river on foot. 

Angling days in July are long, averaging just over 15 hours of daylight a day. The average daily high temperature of 80 degrees F reflects the long days of sunshine. Nightly lows often dip well below 45 degrees F, causing water temperatures on the Stillwater River to remain cool. Around 1.3” of accumulated precipitation falls in July, making it one of the driest months of the year.  

By early June snowpack data in the Beartooth Mountains can provide a best-guess forecast for when the Stillwater River may crest and begin to drop. Because the average annual peak streamflow occurs in late June, by early July the Stillwater River is in prime shape and an exciting option for very experienced floaters or anglers fishing with guides. Wading anglers can enjoy the Stillwater River in early July, but they must be strong waders and exercise caution and safety at all times.  

July fishing: what to expect

The Stillwater River in July is an ideal time to fish for the river’s wild trout. The river flows through sparsely populated Montana ranch lands. Its source lies high in the Beartooth Wilderness so clean and cold water is common on the Stillwater River in July, so when other rivers may be too low or too warm to fish, the Stillwater River is in prime condition.  

Floating anglers can expect to catch plenty of 10- to 12-inch wild trout. Wading anglers can expect the same but must also prepare to cover a lot of water, constantly walking and standing on the river’s uneven boulder-filled streambed. 

Whether floating or wading, the preferred method for catching plenty of trout on the Stillwater River in July is a 7.5- or 9-foot 2X or 3X leader with a size 8 to 10 dry fly fished with two feet of 4X dropper tippet with a size 14 or 16 beadhead nymph. For dry flies, high floating Chubby Chernobyls or foam-bodied attractors are best for the river’s fast and rough currents. For nymphs, beadhead mayfly or caddis imitations are ideal. 

A typical day fishing the Stillwater River in July doesn’t need to start early—water temperatures remain in the high 40 degrees F until mid- or late-morning. As the month progresses and water temperatures slightly rise and stream flows lower, anglers can find more actively feeding trout early in the day and again in the early evening.

Throughout most of the Stillwater River’s length—it flows for over 70 miles—the fish tend to be opportunistic feeders. The river’s fast currents and abundance of trout-friendly habitat produce high numbers of eager trout. Because of this, expectations for fly fishing the Stillwater River in July can be high.

Where to find July trout on the Stillwater River

Trout, and the type of water in which they feed and hold, depend entirely on beneficial stream flows. Because the Stillwater River is a fast-flowing river with pocket water, riffles, and shelves as the primary habitat, knowledge of stream flows is important for finding trout on the Stillwater River in July.

In years with above average mountain snowpack, stream flows may remain above 2,000 cubic feet per (cfs) second for the first half of July. At flows above 2,000 cfs trout will hold in any slow water they can find—eddies, slow water created by bank side structure, or a deep pool. 

When stream flows drop below 2,000 cfs, the Stillwater River’s opportunistic trout hold in very predictable places. Pair the hatches with fast-flowing water and plenty of food, and Stillwater River trout hold and feed in typical fast-water/pocket-water lies. These are: in-front of and behind large rocks 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. 

Trout on the Stillwater River can be found in many places, but because the river is fast-flowing, full of twists and turns, and a few sections of whitewater, safely floating the river’s rapids and rock gardens, and walking-and-wading the river can be a challenge. Walking-and-wading anglers can access the river at any of the public access sites, but anglers need to be prepared to cover some ground to fish enough water to find plenty of trout. 

Important July hatches

Hatches on the Stillwater River in July consist of the usual suspects for a Montana freestone. Golden stoneflies are abundant in early July, Yellow Sally stoneflies can be thick, Pale Morning Dun (PMDs) mayflies are consistent, and caddis in the evenings are strong. With the addition of terrestrials by the middle of the month, the Stillwater River in July has plenty of food for trout which means plenty of options for anglers. 

In most years, Golden stoneflies and salmonflies begin to wane by the second week of July. Yellow Sally stoneflies are abundant on the Stillwater River throughout July. However, because these size 10 to 12 stoneflies have erratic flying behaviors, most trout ignore hatching adults and feed almost exclusively on their nymphs. 

Caddis are thick on the Stillwater River in July. Most of the Stillwater River’s caddis species in July hatch in the afternoon with the strongest emergence occurring in the evenings. Most Stillwater River caddis range in size 12 to 16 and brown or tan. 

Hatches of PMDs begin mid-morning and last for several hours. Insects range in sizes from 12 to 18, with most being size 16. As a mayfly, it is important to understand trout may feed on emerging PMDs and not exclusively on fully hatched adults. 

Terrestrials—insects that live the entirety of their life on land—can provide a large portion of a Stillwater River trout’s diet in July. Spruce moths, grasshoppers, crickets, ants, beetles, spiders, and any other land-dwelling insect that may inadvertently find its way onto the surface is likely to be eaten by a hungry trout on the Stillwater River in July.

Trico mayflies may hatch on the Stillwater River in late July. These small black-bodied and white-winged mayflies are tiny, ranging in size from 18 to 22. Because the Stillwater River is fast flowing and pocket water predominates, fishing tricos on the Stillwater River is best suited for very skilled anglers. 

Stillwater River fly box for July 

Stonefly nymphs in brown and black in sizes 4 to 10

Golden stonefly dry flies in sizes 8 and 10

Yellow Sally nymphs in sizes 10 to 16

Yellow Sally dry flies in sizes 10 to 16

PMD nymphs sizes 12 to 18

PMD emergers sizes 12 to 18

PMD dry flies sizes 12 to 16

Caddis pupae sizes 12 to 16

Caddis CDC emergers sizes 12 to 16

Caddis dry flies with dark grey, black or brown bodies in sizes 12 to 18; 

Grasshoppers in sizes 4 to 12

Ants and beetles in sizes 12 to 18

Spruce moths in sizes 12 to 16

Trico nymphs size 18 to 22

Trico emergers sizes 18 to 22

Trico dry flies sizes 18 to 22

Streamers in white, yellow, or brown in sizes 2 to 6