October Fishing on the Yellowstone River

October Weather, stream flows, and summary

The Yellowstone River in October may be the swan song for the angling season, but it is far from playing second fiddle. During this final month of the angling calendar, anglers can experience some exceptional dry fly fishing—with small and large flies—and have an opportunity to catch a trophy-sized brown trout. 

This is the month of Blue Winged Olives, big trout chasing streamers, and a slight possibility of October caddis. The long, sunny days of summer are gone. Busy boat ramps and numbers-hungry anglers are also most likely absent, making October on the Yellowstone River the month for anglers who appreciate fishing a river back-dropped by fall colors and fresh snow on mountain peaks and the possibility of large trout. 

October weather is diverse—from days of bright sunshine and highs in the 60s to blizzards and highs in the teens. The law of averages abides and the average daily high temperature hovers around 58 degrees F. There is slightly less rain in October than September with an average of 1.2” and the possibility of snow increases with an average of 0.3” inches. Quality fishing opportunities can occur in these variable weather conditions, and often the lousiest weather produces the best October fly fishing. 

Streamflows are consistent and clear on the Yellowstone River in October. Unlike September when a thunderstorm or rain shower can cause the Lamar River—a major tributary of the Yellowstone—to become muddy, any precipitation falling in the Lamar River headwaters usually falls as snow. 

For many anglers October and the regular occurrence of fall-like weather means a commitment to fishing streamers for aggressive brown trout. The Yellowstone River in October is exactly that—a river ideally primed for targeting large trout with large flies…and a river that often gives up its bounty to those anglers committed to fishing large streamers. October is the month streamer addicts benefit from a “large-flies-means-large-fish” mentality. 

In October Blue Winged Olives (BWOs) are the primary hatch on the Yellowstone 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. 

Planning to fish an October caddis hatch is more speculative than expectation. October does see a few days of sunshine and warm air temperatures above 65 degrees F, if this does happen terrestrials can become active for a brief timeframe.

October fishing: what to expect

As the saying goes, there is never bad weather, only bad gear. On the Yellowstone River in October, this is certainly the case. Sun, rain, and snow can all happen on the same day. And many days the worst weather creates the best fishing conditions. Blue Winged Olives tend to hatch in rainy or snow weather. Brown trout, especially large brown trout, are inherently more sensitive to bright sunshine in the fall. Fishing in cold, rainy, or snowy weather may not be what you desire as enjoyable but armed with quality gear and a good attitude it can pay dividends. A typical day fly fishing the Yellowstone River in October begins in the mid-morning. The need for an early start is gone because if Blue Winged Olives hatch they will begin around mid-morning or late afternoon. For streamer anglers, large brown trout may be active early, but the sun rises between 7 and 8 AM most mornings in October so early starts are not crucial. Tandem two-fly nymph rigs still catch most fish in October, but on the Yellowstone River in October streamers and BWOs take the cake. 

Yellow, brown, black, and olive streamers are the color choices for October trophy-sized trout. 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.

Dry fly anglers can also delight as hatches of Blue Winged Olives are a common occurrence. The entire river from Gardiner down to Columbus is known for strong hatches, but the bulk of the BWO emergence occurs on the river between Big Timber and Emigrant. When conditions line-up appropriately, typically a forecast for light rain or snow flurries coupled with low winds, a strong BWO hatch may occur. 

Where to find October trout on the Yellowstone

Yellowstone River trout in October can be found in a variety of locations. Nymphs—mayfly, caddis, and stonefly nymphs—are active in the Yellowstone River year-round. Unless there is a strong emergence of Blue Winged Olive mayflies, trout will be found in subsurface holding lies.  

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. 

If sunshine is abundant and the air temperature hovers near 60 degrees F or higher, the slight possibility exists for a few trout to still target terrestrials. Trout will expend vital energy and take the risk from deep cover for a morsel as large a grasshopper, ant, or beetle. These large offerings may not pass by again that day. Fishing grasshoppers in October is a rarity but it does happen. 

As the month grows, hatches of BWO mayflies can increase and brown trout grow even more aggressive prior to fall spawning. 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. 

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.

Important October hatches

October hatches on the Yellowstone River are less in scope and scale than other months. However, the main hatch of October—Blue Winged Olive mayflies—can be quite strong at the right place and the right time. Overcast, rainy or snowy days see the strongest emergence. An overcast day with light winds can mean the dry fly fishing on the Yellowstone River can be quite 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 Yellowstone 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.  

October caddis also hatch on the Yellowstone River. These bugs may be large in size—about size 8—but their hatch is 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. 

Yellowstone 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