October Fishing on the East Gallatin River

October weather, stream flows, and summary

October on the East Gallatin River is designed perfectly for the fishery that it is—a small freestone near an urban area. With hatches of Blue Winged Olive (BWOs) mayflies occurring mid-day and plenty of aggressive brown trout, anglers on the East Gallatin River can typically find something up their alley. 

October weather on the East Gallatin River includes everything from days of bright sunshine and highs in the 60s to blizzards and highs in the teens. When the month is done, the law of averages nearly always wins and the average daily high temperature hovers around 58 degrees F. 

There is slightly less rain in October than September with an average of 1.1” and the possibility of snow increases with an average of 0.4” inches. Quality fishing opportunities can occur in these variable weather conditions, and often the lousiest weather produces the best hatches or aggressive trout on the East Gallatin River. 

Stream flows are consistent and clear on the East Gallatin River in October and hover around 60 to 70 cubic feet per second (cfs) throughout the month. Because fishing from a boat is not allowed on the East Gallatin River, anglers need to be prepared to cover a lot of ground on foot. However, landowners on the East Gallatin River are not very friendly to anglers, so be prepared to stay in the streambed and obey the Montana Stream Access Law at all times.  

October fishing: what to expect

Sun, rain, and snow can all happen in the same day so anglers must be prepared for inclement weather. Typically in October the days with the worst weather can have the best fishing conditions. Blue Winged Olives (BWOs) most likely will hatch in rainy or snow weather. Fishing in rain or snow may not be your vision of Montana fly fishing, but with quality gear and a good attitude it is often the difference between success or failure for fly fishing the East Gallatin River in October.

A typical day fly fishing the East Gallatin River in October begins mid-morning. If Blue Winged Olive (BWOs) mayflies 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 anglers targeting brown trout with streamers or subsurface rigs should dress for some cool mornings. Tandem two-fly nymph rigs still catch most fish in October, but on the East Gallatin River in October streamers and BWOs are the method of choice for local anglers. 

Yellow, brown, and black streamers are the color choices for October streamer fishing. Most large fish are caught while dead-drifting a large streamer below a strike indicator or dragging a large streamer off the bank. 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.

The entire river from Bozeman downstream to its confluence with the main Gallatin River is known for strong hatches. When conditions line-up appropriately, typically a forecast for light rain or snow flurries coupled with low winds, a strong BWO hatch may occur. Always have plenty of size 18 parachute mayfly patterns and quality floatant. 

Where to find October trout on the East Gallatin

East Gallatin River trout in October can be found in a variety of locations. Nymphs—mayfly, caddis, and stonefly nymphs—are active in the East Gallatin River in October even if adults are not hatching. Unless there is a strong emergence of Blue Winged Olive (BWOs) mayflies, trout will be found exclusively in subsurface holding and feeding lies.  

Even on an overcast day when a BWO hatch is imminent, fishing tandem nymph rigs is the most common way to catch fish prior to a hatch. 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. 

If sunshine is abundant and the air temperature hovers near 60 degrees F or higher, the slight possibility exists for trout to still target terrestrials. Trout may rise from deeper water to slurp a large grasshopper, ant, or beetle. Fish eating grasshoppers and other terrestrials in October is a rarity but it does happen. 

Hatches of BWO mayflies increase as October grows and brown trout grow even more aggressive prior to fall spawning. BWO nymphs can be found throughout the river and 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. Most BWO hatches occur mid-day or early afternoon. 

If seeking one of the East Gallatin River’s larger brown trout, target 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.

Important October hatches

October hatches on the East Gallatin River can be thick, but the variety of species is small compared to other months. The main hatch of October—Blue Winged Olive (BWOs) mayflies—need lousy weather for a strong emergence. Overcast, rainy or snowy days are ideal for dry fly fishing in October on the East Gallatin. 

Fall season BWO mayflies are slightly smaller than the insects that hatch in spring. 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 consistent dry fly fishing opportunities.

Even if BWOs are not hatching, The East Gallatin River is home to a healthy population of stoneflies, 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.  

A few terrestrials—insects that live on land but may land in the water—may be active in early October if prolonged warm days exists and sunshine is prevalent. 

October caddis also hatch on the East Gallatin River. These bugs are approximately size 10 and their hatch is very sporadic. In a day of angling 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. 

East 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 10

Crayfish patterns sizes 6 to 10

Sculpin patterns sizes 6 to 10

Streamers in yellow, black, or brown sizes 6 to 10