September Fishing on the Ruby River

September weather, stream flows, and summary

During September on the Ruby River anglers have an opportunity to fish one of southwest Montana’s most special small rivers. With stream flows that are ideal for walk-and-wade fishing, the Ruby River is tailor-made for spectacular days. However, there is a catch: most of the Ruby River flows through private property. Plus, the river has thick brush-covered banks, deep holes and pools, making it virtually impossible to walk-and-wade without stepping onto private property. 

For anglers wanting to fish a small mountain freestone, the Ruby River that flows high in the mountains of Beaverhead-Deer Lodge National Forest will be pleased with the population of 10” to 12” wild trout. But for anglers desiring some exciting summer- and fall-like fishing for brown trout, gaining access on the Ruby River downstream of Ruby Dam is the most challenging aspect of fly fishing the Ruby River in September. 

In both sections of the Ruby River—upstream of Ruby Reservoir and downstream of Ruby Reservoir—public access points are limited. And when access is obtained through a public access site, anglers must be very considerate of Montana’s access law because landowners are diligent in ensuring anglers do not trespass. Below Ruby Reservoir, the river twists and turns for nearly 50 miles through hay fields and thick willow-swamped wetlands.  

September weather on the Ruby River can be all four seasons in one day—snow, rain, sunshine, then snow again. From start to finish, the daily high temperatures have a broad range—from 80 degrees F in early September to around 60 degrees F by month’s end. Precipitation is a little higher than August, with about 1.3” of rain and snowfall up to 2” in the Beaverhead-Deer Lodge National Forest. Because the weather can be so varied in September anglers need to be prepared for changing weather conditions.   

With stream flows typically well below 200 cubic feet per second (cfs) anglers can fish a small, trout-filled river that is in prime condition. However, very little public access combined with the nature of the river itself—abundant deep bends and deep holes and thick bank-side brush cover—make it very difficult to walk-and-wade fish the Ruby River without stepping onto private property. 

September fishing: what to expect

From the start of September to the start of October, the Ruby River changes dramatically. Because stream flows are low and water temperatures are well below 65 degrees F, September is arguably the best month to fly fish the Ruby River. Access is challenging, but September does provide the most opportunity for anglers willing to cover some ground on foot. Unless fishing in the Beaverhead-Deer Lodge National Forest, anglers must be very conscious of staying below the mean high-water level. 

Both sections—above Ruby Reservoir and below Ruby Reservoir—will fish similar in September. Both sections in the first half of the month will fish more like summer than fall. Fish may be active before the sun is high overhead. Start the day fishing a dry fly because grasshoppers, ants, beetles, and spruce moths—only in the Beaverhead-Deer Lodge National Forest section—may still be prevalent. Nights in September are cool, taking a few hours for the morning chill to subside. A tandem nymph rig or slowly dragged or swung streamer may entice more fish to strike than might be willing to rise to a dry fly.

For nymphs choose mayfly or caddis patterns in sizes 12 to 18, preferably beadheads. For streamers, choose beadhead or conehead in olive or black or brown patterns in sizes 2 to 6. In September, Ruby River trout also like yellow and brown articulated patterns. 

In early September, terrestrial fishing should be consistent on the Ruby River as the sun warms the riverside grasses and trees. For anglers willing to commit to fishing terrestrials, early September can be the best few weeks of the year. 

Between September 15th and 20th, the first major cold front of the fall season passes through. When this occurs, brown trout begin to prepare for their spawn and become more aggressive. These larger trout actively seek out prey. Anglers committed to fishing streamers can find some of the largest brown trout of the year. This is especially true on the river downstream of Alder, but access to this water is very difficult. 

After September 15th nights are markedly longer and cooler than earlier in the month. Hatches of Blue Winged Olive (BWOs) mayflies can occur, but usually do not begin until mid- or late-morning. 

Anglers seeking large brown trout may consider an early morning start as well and drag or slowly strip large streamers. With the colder water temperatures of late-September, the early bird rarely gets the worm as most trout are active later in the day. 

Even into the second week of September, hatches of caddis in the evenings can be very prolific on the Ruby River in September, and anglers willing to fish into darkness can find success.  

Where to find September trout on the Ruby River

During September, the trout will be located where the easiest available food is also located. And, this is directly related to weather. Daily high air temperatures are lower than August, water temperatures in September are also lower. However, because early September can still experience warm daily high temperatures, trout can be found in a variety of places. 

On the Ruby River the first few weeks of September will be more like summer. Because the river’s surrounding hay fields are still thick with grass, grasshoppers, ants, crickets, and beetles all provide food for trout. A few sporadic spruce moths may hatch on the river in Beaverhead-Deer Lodge National Forest, but most dry fly fishing in early September will be with grasshoppers, ants, crickets, and beetles.

Nymphs—mayfly, caddis, and stonefly nymphs as well as midges—are active in the Ruby River year-round. In early September’s summer-like conditions of bright sunshine, trout are most likely going to be found in subsurface holding lies. If fishing tandem nymph rigs in early September, focus on the heads of deep pools, drop-offs around structure, behind or in front of structure, or any place that can provide cover from predators or fast currents.

As the middle of the month comes and October gets closer, terrestrial fishing will dwindle but hatches of Blue Winged Olive (BWOs) mayflies can be very thick. When BWOs are thick look for trout in slower currents such as the inside of river bends, seams behind rocks, and slower runs below riffles. With the season’s first cold front, brown trout also begin to grow aggressive prior to fall spawning. 

After the first cold front passes, look for brown trout in the usual predator hangouts—rip-rap banks, the heads of deep holes near the many bends that occur in the Ruby River, deeper water near shallow water, hiding near structure, or along a cut bank. Although most brown trout will spawn in October or November, a few browns may begin spawning in late September. They may be found on their redds on shallow gravel bars. Please avoid targeting spawning trout when they are encountered.

Important September hatches

September on the Ruby River is prime time as a variety of hatches and aggressive brown trout make for an exciting month. Caddis hatches along with terrestrials can provide action early in the month, but the appeal of September is the emergence of Blue Winged Olive mayflies and predatory brown trout on streamers. 

In the first half of the month, the weather can still be warm and terrestrial fishing can be quite reliable. Terrestrials are insects that live the entirety of their life on land. Grasshoppers, ants, spruce moths—on the section in Beaverhead-Deer Lodge National Forest—beetles, spiders, crickets, and any other land-dwelling insect that may inadvertently finds its way into the river could end up as trout food.

Blue Winged Olive (BWOs) mayflies can hatch after the first cold front passes through, typically around September 15th. A cool, slightly rainy or overcast day is ideal for a strong emergence of BWOs. These mayflies are slightly smaller than their spring season cousins. Ranging in size from 16 to 22, these insects will emerge by late-morning or early afternoon and can provide a few hours of dry fly fishing opportunities. 

Rounding out the hatches during September include a few caddis hatches in early September and the occasional early October caddis in late-September. 

Towards the end of September, as many of the Ruby River’s brown trout prepare to spawn, dedicated streamer anglers can pursue opportunistic and aggressive brown trout. 

Ruby River fly box for September

Caddis pupae sizes 14 to 18

Caddis CDC emergers sizes 14 to 18

Caddis dry flies with tan or brown bodies sizes 14 and 18 

Grasshoppers sizes 4 to 14

Crickets in sizes 8 to 12

Ants in brown, cinnamon, and black sizes 12 to 20

Beetles in black sizes 10 to 18

Spruce moths mottled in tan or grey in sizes 12 to 16

BWO dry flies sizes 16 to 22

BWO emergers sizes 16 to 20

BWO nymphs sizes 16 to 20

Stonefly nymphs in brown and black sizes 4 to 10

October caddis size 8

Crayfish patterns sizes 2 to 8

Sculpin patterns sizes 2 to 6

Streamers in olive, black or brown sizes 2 to 6