October Fishing on the Bighorn River

October weather, stream flows, and summary

As the last month of the angling season on the Bighorn River, during October the crowds are less, the heavy weed growth of September has died and floated away, and the length of sunlight during an angling day is much shorter. This adds up to a month that offers anglers a pleasant combo of consistent flows and predictable hatches. October on the Bighorn River is the month for anglers who appreciate fishing a river back-dropped by fall colors and in a different mood than when most anglers fish. 

Blue Winged Olive (BWOs) mayflies and streamers headline the fishing reports throughout the month of October. Floating and walk-and-wade fishing are both viable options for anglers. With the cooler water temperatures of fall, the Bighorn River’s thirty miles of trout-filled water can produce any day of the month. From the Afterbay Access to Mallards Landing, the Bighorn River’s 4,000 trout per mile provide ample opportunity for a bend in the rod. Similar to other months, the river’s upper thirteen miles of river are home to the most fish, but anglers desiring solitude will surely find it on the river downstream of Bighorn Access Site. 

October weather is diverse—from days of bright sunshine and highs in the 70s to blizzards and highs in the twenties. The law of averages rules in October and the average daily high temperature hovers around 60 degrees F. There is slightly less rain in October than September with an average of 0.9” and the possibility of snow increases with an average of 0.2” inches. Quality fishing opportunities can occur in these variable weather conditions, and often the lousiest weather produces the best October fly fishing on the Bighorn River.

Stream flows average a little more volume in October compared to September, with releases averaging around 3,000 cubic feet per second (cfs) throughout the month. With the consistent stream flows and clean water—most of the weeds have died—October means a commitment to fishing streamers for aggressive brown trout. 

In October Blue Winged Olives (BWOs) are the primary hatch on the Bighorn River. A few October caddis are spotted but they are not consistent and emerge in small numbers, usually one or two at a time compared to the thousands of insects during a BWO hatch. 

With winter creeping in, October on the Bighorn River provides anglers a last chance to fish this southeastern Montana tailwater before hatches dwindle and fish transition to winter feeding habits and lies. Even if a cold-front passes through, water temperatures often remain in the 40 to 50 degree F range, which is ideal for hatches of BWOs and aggressive brown trout chasing streamers. 

October fishing: what to expect

A typical day fly fishing the Bighorn River in October doesn’t need to begin until mid-morning. The primary hatch of October—Blue Winged Olive (BWOs) mayflies—begins around mid-morning and trout often do not actively begin feeding until BWO nymphs become active. There are exceptions to this as some big brown trout can be caught on streamers during the low-light hours of morning. 

Sun, rain, and snow can all happen on the same day. And many days the worst weather creates the best fishing conditions. BWOs tend to hatch in rainy or snowy weather. Brown trout, especially large brown trout, are inherently more sensitive to bright sunshine in the fall. Fishing in cold, rainy, or snowy weather are the favored conditions for Bighorn River regulars in October. 

Yellow, brown and yellow, black, and olive streamers are the color choices for streamers in October. Dead-drifting a large streamer below a strike indicator or dragging a large streamer through many of the Bighorn River’s long riffles and runs are proven tactics. Many anglers will also trail a smaller nymph such as a size 16 or 18 mayfly nymph, creating a two-fly rig designed to entice a big brown trout or catch a selective rainbow or brown trout.

Hatches of Blue Winged Olives are a common occurrence on the Bighorn River in October. When conditions line-up appropriately, typically a forecast for light rain or snow flurries coupled with low winds, a strong BWO hatch may occur. 

Scuds, sowbugs, and midges are active year-round on the Bighorn River. Scuds and sowbugs are subsurface aquatic insects. Midges are primarily subsurface, although trout will occasionally feed on hatched adult midges. Bighorn River trout will feed on hatching midges, but most trout feed subsurface during a midge hatch. Scuds and sowbugs make up a substantial portion of Bighorn River trout’s diet and any angler fishing the Bighorn River should have several patterns, such as Ray Charles, Firebead sowbugs, and Carpet Bugs. 

Where to find October trout on the Bighorn

Because stream flows in October are rarely above 3,000 cubic feet per second (cfs), until a hatch occurs, fishing tandem nymph rigs is the most common way to catch fish. Focus on deep water near shallow water, in the middle of the numerous long runs, or the inside corners of deeper holes, behind or in front of structure, or any place that can provide cover from predators or fast currents. 

During October streamer fishing for brown trout can be some of the best fishing of the year. With nearly 4,000 trout per mile, odds are good a well-presented streamer will be seen by a hungry trout. For big brown trout, target areas where they can ambush unsuspecting prey—deeper water near shallow water, hiding near structure, or along a cut bank. Please also be aware that many brown trout may begin to spawn in October. These spawning fish may be found redds on shallow gravel bars. Please avoid targeting spawning trout when they are encountered.

If sunshine is abundant and the air temperature is above 60 degrees F or higher, a few trout may eat terrestrials. Because it may be months before food as large as a hopper floats by, trout may expend vital energy for a morsel as large as a grasshopper, ant, or beetle. These large offerings may not pass by again that day. 

On any day in October the potential for strong hatches of Blue Winged Olive (BWOs) mayflies. BWO nymphs can be found throughout the river, but when water temperatures hover between 48 and 52 degrees F, expect a hatch. When a strong hatch occurs, look for trout in slower currents and “softer water” such as the inside of river bends, seams behind rocks, and slower runs below riffles. 

Important October hatches

Hatches on the Bighorn River in October pale in comparison to the plethora of activity in summer. However, there is one hatch that draws many anglers to the river in October—Blue Winged Olive (BWOs) mayflies. Overcast, rainy or snowy days see the strongest emergence. On an overcast day with light wind, the dry fly fishing on the Bighorn River can be very reliable, bringing plenty of fish to the surface to feed. 

Fall season BWO 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 provide a few to several hours of dry fly fishing opportunities.

Even if BWOs are not hatching, The Bighorn River is home to a healthy population of scuds, sowbugs, midges, mayflies, and caddis whose nymphs are active year-round. These nymphs are available to feeding trout and best fished with two-fly weighted nymph rigs.  

October caddis also hatch on the Bighorn River. These bugs may be large—about size 8—but their hatch is sporadic. In a day of angling, only a few October caddis may be seen fluttering in the air, but committing to a large dry fly can bring the occasional opportunistic trout to the surface. 

Bighorn River fly box for October

BWO dry flies sizes 18 to 22

BWO emergers sizes 18 to 20

BWO nymphs sizes 18 to 20

Scuds and sowbugs size 16 to 22

Midges, primarily subsurface, size 18 to 22

October caddis size 8

Crayfish patterns sizes 2 to 8

Sculpin patterns sizes 2 to 6

Streamers in yellow and brown, yellow, black or brown sizes 2 to 6