October Fishing on the Montana Spring Creeks

October weather, stream flows, and summary
October is the closing chapter to consistent dry fly fishing opportunities on the Paradise Valley Spring Creeks, but with the potential for strong hatches of Blue Winged Olive (BWOs) mayflies existing every day, Nelson’s, DePuy’s, and Armstrong’s spring creeks should be experienced by any angler who enjoys matching the hatch or sight-fishing to subsurface feeding 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 on the spring creeks can occur in these variable weather conditions, and often the lousiest weather produces the best October fly fishing. 

Because the enjoyment of fishing the spring creeks in October hinges on the opportunity to fish small dry flies, wind can play a factor in a day’s fishing on the spring creeks. Because the ideal day on the spring creeks is shaped by a hatch of Blue Winged Olive mayflies, if winds in excess of 15 MPHs are forecast, many of the hatching dry flies are unable to stay on the water as they get blown off before a trout can consume them. Plus, long leaders that are essential for success are a little more difficult to cast. On windy days, knowledge of the creeks is essential, as plenty of sections exist that may be tucked away or out of the prevailing wind.

Even though the spring creeks remain clear and a consistent temperature year-round—they bubble out of the ground at approximately 52 degrees F—October is the final month of the year with predictable hatches. After October very sporadic hatches of midges provide the occasional dry fly bite.

October fishing: what to expect
October on Nelson’s, DePuy’s, and Armstrong’s spring creeks is all about strong hatches of Blue Winged Olive (BWOs) mayflies and consistent action with midges—but most midge action will be with subsurface flies. A typical day fishing Nelson’s, DePuy’s, or Armstrong’s spring creeks in October often begins fishing a shallow-water, sight-fishing nymph rig with size 18 or 22 midge or mayfly nymphs. Long leaders of 12- to 15-feet are best, tapered to 5X or 6X fluorocarbon tippets. Around mid-day the BWOs begin to hatch and anglers with moderate casting ability will switch to targeting trout eating BWOs on the surface. 

A strong BWO hatch can last up to four hours, but most BWO hatches in October last around two to three. BWOs on the spring creeks are sizes 18 to 22. Dry fly anglers should be armed with supple tippets in sizes 5X and 6X, plenty of quality floatant that works well with CDC, and the ability to execute a reach cast.

If BWO adults are not on the water and fish are not rising, but trout can still be spotted feeding subsurface, fish a tandem, shallow water rig on a 12- or 15-foot leader tapered to 5X or 6X fluorocarbon tippet with a size 18 or 20 mayfly nymph. If BWOs are not present at all, scud, sowbug, or midge patterns can produce fish. Most experienced spring creek anglers use small yarn or light pinch-on indicators and small size—6 to 12—split shot. Because most currents on the spring creeks run slower than larger rivers, less weight and shorter depths from fly to indicator are essential. Successful patterns include Wondernymphs, JuJu Baetis, Zebra midges, and WD-40s. 

Streamer anglers may find some success in October, but most spring creek trout consistently eat dozens of small flies rather than a few larger flies. Think of them as foragers rather than predators. But if fishing a streamer is desired choose one that is sparsely tied and loosely weighted. 

All three of the Paradise Valley Spring Creeks are important spawning habitat for brown trout that live in the Yellowstone River, and October is the start of their spawning season. To ensure the long-term health of the Yellowstone River’s brown trout populations do not target actively spawning trout or trout near redds. Be extremely cautious while walking-and-wading and avoid walking on redds or fishing in the vicinity of redds. Redds are sections of small, cobble in the stream bed cleared by spawning fish. Additionally, if a spawning or spawned-out trout—skinny, dark in color and has the appearance of looking beat-up and tired— is caught, please release as quickly as possible.

Where to find October trout on Nelson’s, DePuy’s, and Armstrong’s spring creeks
Finding trout in October on the spring creeks is easy if there is a strong hatch of Blue Winged Olive (BWOs) mayflies. Just look for rising fish and bring your reach cast and you’ll get ‘em. When a strong hatch occurs, look for fish in slow current seams, on shallow flats, a slow seam next to a fast seam, any shallow water adjacent to any deep water, eddy lines, and seams behind rocks or seams created by faster water being slowed down by slow water. 

But if a hatch of Blue Winged Olive (BWOs) mayflies doesn’t occur, most spring creek trout will be in deeper water. In October this deeper water provides plenty of food—remember food is abundant on the spring creeks—and cover from overhead predators. Deeper water is water that is between three and six feet deep with medium slow current—about the pace of a normal walk. In this deeper, slower water, fish are probably eating midges, scuds, sowbugs, or mayfly nymphs.

If fish are not rising or actively feeding near the surface, it is highly likely they are still feeding on mayfly nymphs or midge pupae. Target any change in current speed or change in depth, such as a bucket or small depression where the depth may be a foot or so deeper than the nearby bottom structure. Plus, with the crystal clear water of the spring creeks, sight-fishing is a daily occurrence, so be prepared to actively pursue specific fish—it just may be with shallow, lightly weighted nymph rigs rather than the large indicator rigs so common on larger rivers. 

Beginning in October migratory brown trout from the Yellowstone River may venture in the spring creeks to spawn. Be extremely cautious while walking-and-wading and avoid walking on redds or fishing in the vicinity of redds. Redds are sections of small, cobble in the stream bed cleared by spawning fish. Additionally, do not cast to or target actively spawning fish.

Important October hatches for Nelson’s, DePuy’s, and Armstrong’s spring creek
October on the spring creeks is primarily about hatches of Blue Winged Olive (BWOs) mayflies. There are sporadic hatches of October caddis and consistent hatches of midges, but it is the BWOs that excite anglers and trout on Nelson’s, DePuy’s, and Armstrong’s spring creeks in October. 

The October emergence of BWOs on the spring creeks can happen on any day during October. Overcast, rainy or snowy days see the strongest emergences. These mayflies are slightly smaller than their spring season cousins. Ranging in size from 18 to 22, they often emerge by late-morning or early afternoon and provide a few to several hours of dry fly fishing opportunities.

October caddis can also hatch on the spring creeks, 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. 

Midges, whose larvae, make up a large portion of a spring creek trout’s diet begin to hatch in abundance in late October. Fishing midge dry flies on the spring creeks has a small, but devoted following. Hatches occur mid-day and can be thick. Zebra midges, WD40s, Tung Teasers, and the Red-and-Black Midge, in sizes 18 to 22 are all good patterns best fished subsurface as part of two-fly nymph rig. 

Paradise Valley Spring Creeks fly box for October
BWO dry flies size 18 to 22

BWO emergers size 18 to 22

BWO nymphs size 18 to 22

Grasshoppers in tan, grey, or light yellow in sizes 10 through 16

Ants, black or cinnamon, in sizes 16 to 18

Beetles, hi-vis black, in sizes 16 to 20

Crickets in black in sizes 10 and 12

October caddis in size 10

Scuds in sizes 18 through 22

Sowbugs in sizes 18 through 22

Midges in sizes 18 through 22

Streamers in olive, black, or brown in sizes 2 to 6