October Fishing on the Gallatin River

October weather, streamflows, and summary

Gone are the crowds of summer, many locals are in the mountains hunting four-legged animals, and anglers not wanting to walk-and-wade are found on the larger rivers. The Gallatin River in October may be small in comparison to its glamorous summer-time reputation of big dry flies and fast water, but it shouldn’t be overlooked. For anglers desiring a river that can serve up hatches, a little bit of earned solitude, and the potential for a trophy-sized trout, the Gallatin River from its confluence with the Madison and Jefferson Rivers to its source high in the mountains of Yellowstone National Park, can feel like the perfect trout stream. 

Because the Gallatin River flows for nearly 90 miles, October weather on the Gallatin River is varied. With days of bright sunshine and highs in the 70s to blizzards and highs in the teens, the Gallatin River is a cornucopia of conditions in October. Average daily high temperatures hover around 50 degrees F. There is slightly more precipitation in October than September with an average of 1.3” and the possibility of snow increases substantially with a 2” on average. Quality fishing opportunities can occur in these variable weather conditions, but in October often the lousiest weather produces the best fishing. 

Streamflows are consistent and clear throughout the river’s length and water temperatures are rarely too cold or too warm, creating an ideal month for dry fly fishing, subsurface nymph fishing, and fishing streamers. Rarely does the Taylor Fork—a tributary of the Gallatin River susceptible to muddy conditions after a heavy rain—create a muddy river because in the Taylor Fork drainage snow typically falls instead of rain. 

Blue Winged Olives (BWOs) are the primary hatch of October. 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. Streamer anglers can find aggressive brown trout, especially on the river in Gallatin Valley. Terrestrials may be an option early in the month but by mid-October a few cold fronts have passed through the drainage. These cold fronts paired with frosty mornings usually put an end to any terrestrials landing on the water. 

October fishing: what to expect

Because the weather can vary from day to day or hour to hour, and the hatches can be sparse or thick, and the brown trout can be on the chase or not, fly fishing the Gallatin River in October is best enjoyed with the correct attitude. Hatches can be strong or they can be sparse. Fishing in cold, rainy, or snowy weather may not be what you find as enjoyable but armed with quality gear and a good attitude it just might pay dividends.

Sun, rain, and snow can all happen on the same day. The worst weather can create the best fishing conditions as Blue Winged Olives (BWOs) tend to hatch in rainy or snow weather. Brown trout, especially large brown trout, are inherently more sensitive to bright sunshine in the fall, so the shorter days—less direct sunlight on the water—means more active brown trout. 

A typical day fly fishing the Gallatin River in October can begin at a reasonable hour. For the dry fly angler, the need for an early start is gone because if BWOs hatch they will begin around mid-morning or late afternoon. Large brown trout may be active early, but the sun rises between 7 and 8 AM most mornings in October so even for the hardcore streamer angler, early starts are not crucial. Tandem two-fly nymph rigs still catch plenty of fish in October, but October is the month for streamer and dry fly anglers. 

Olive, black or brown streamers are the go-to choices for October trophy-sized trout. Favorite tactics include dead-drifting a large streamer below a strike indicator or dragging a large streamer off the bank or through a deep run or pool. 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.

Dry fly anglers can also delight as hatches of BWOs are a common occurrence. When conditions line-up appropriately, typically a forecast for light rain or snow flurries coupled with low winds, Gallatin River trout feed actively on hatching BWOs. October caddis hatch sporadically on the Gallatin River this month as well, but most dry fly anglers will pursue BWOs. 

Where to find October trout on the Gallatin

Similar to September, trout on the Gallatin River in October follow the available food source. Until a hatch occurs, fishing tandem nymph rigs is the most common way to catch fish. Focus on deep water near shallow water, behind or in front of structure, or any place that can provide cover from predators or fast currents. Nymphs—mayfly, caddis, and stonefly nymphs—are active in the Gallatin River year-round. Unless a hatch of Blue Winged Olives (BWOs) is strong, trout will be found in subsurface lies. 

When fishing tandem nymph rigs, focus on the deeper water near shallow water, behind or in front of structure, or any place that can provide cover from predators or fast currents. If sunshine is bright and strong and the air temperature hovers near 60 degrees F or higher, consider fishing terrestrials. Trout will expend vital energy and take the risk from deep cover because a morsel as large as a grasshopper, ant, or beetle may not pass by again that day or that season. Fishing grasshoppers in October is a rarity but it does happen. 

As the month progresses hatches of BWO mayflies can increase and brown trout grow even more aggressive prior to fall spawning. From the river in Yellowstone National Park downstream through Gallatin Valley, trophy-sized brown trout can be found in the usual predator hangouts—deeper water near shallow water, hiding near structure, or along a cut bank. Many brown trout will begin to spawn in October. These spawning fish may be found on their redds on shallow gravel bars. Please avoid targeting spawning trout when they are encountered.

BWO nymphs can be found throughout the river. 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

October hatches on the Gallatin River are relatively small compared to other months. The Gallatin River is home to a healthy population of stoneflies, mayflies, and caddis whose nymphs are active year-round, so even if the insects are not hatching, the nymphs are available to trout. 

In October the emergence of fall Blue Winged Olive (BWOs) mayflies is the primary hatch. These small mayflies can hatch on any day during October. Overcast, rainy or snowy days see the strongest emergence. Ranging in size from 16 to 22, these mayflies are slightly smaller than their springtime cousins. Fall BWOs emerge by late-morning or early afternoon and provide a few hours of dry fly fishing opportunities.

October caddis also hatch on the Gallatin River, but primarily on the river north of Big Sky and down through Gallatin Valley. These bugs may be large in size—about size 8—but their hatch is sporadic at best. During any day of angling in October only a few October caddis may actually be seen fluttering in the air but committing to a large dry fly can bring the occasional opportunistic trout to the surface. 

Gallatin River fly box for October

BWO dry flies sizes 16 to 22

BWO emergers sizes 16 to 20

BWO nymphs sizes 16 to 20

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