Introduction to Fly Fishing Montana in Early Fall

Fly fishing in Montana in early fall requires anglers to be ready to fish in a time of transition. This period, which begins with the first frosty nights in late August or early September and extends through the first extended cold at the end of September or early October. On hot days, the fish act like it’s summer. On cold days, they act like it’s late fall. When the weather is in-between, it’s a mix of the two.

Regardless of the day-to-day weather, the brown trout start to get very frisky at this time, the fall hatches begin in earnest, the terrestrial bite becomes shaky (particularly after September 20 or so), and water temperatures drop out of the late summer danger zone, if they ever got there. The water is now low and clear as glass everywhere, leading to spooky fish, though often spooky fish that feed aggressively.

Just about everything in the Yellowstone Country Fly Fishing operations area fishes well in early fall except most lakes and smaller creeks, though which days in early a fall a given body of water will produce best varies. The Firehole might be great during an early cold snap in September but very tough on a bright, warm day late in the month, for example. As such, fly fishing Montana in early fall is a good time for anglers willing to fish where conditions dictate, using the tactics conditions dictate. It’s not a good choice for anglers who want to fish one place with one preferred technique

Here’s one thing early fall is not: a time to find solitude on popular rivers, particularly walk-wade rivers in Yellowstone Park. Many anglers come shortly after Labor Day and are shocked to see summer crowds. This is now to be expected. Everyone trying to get away from the summer crowds by coming a few weeks later creates a new crowd in the first half or three weeks of September.

If you want to really shed crowds, come after September 20 or even in October. There’s also sometimes a “sweet spot” between the summer crowds and the early fall crowds. This usually occurs in the last ten days of August. River floats also tend to be less busy that wading (guided or unguided) in Yellowstone Park. In the park, the most crowded waters are those right next to the road or those close to it that hold fall-run brown trout. The Yellowstone River in its canyons can be devoid of people by mid-September away from the few easy accesses.

Weather and Water Conditions

As noted above, weather and water conditions can be all over the map in early fall, and the calendar has little to do with determining the weather. It is not uncommon for it to be colder in the first week of September than the first week of October, for example. Suffice it to say that you should be prepared for everything after about August 20. The highs might be in the 30s or the 90s, the lows in the teens or the 60s. The daily range is particularly broad in early fall: it’s not at all unusual for nights to produce a little light frost even at low elevations, while daytime highs might flirt with 75 or 80 degrees.

In other words, pack layers. Also bring a warm hat and gloves from here on out.

One constant of fall weather is that the region typically sees at least one multi-day storm. This storm brings snow to the high mountains and cold rain with daytime highs that might not crack 40 degrees in the valleys. This storm is most common within a few days of the fall equinox, but it can happen any time.

Water conditions are more consistent save when heavy rains raise levels on freestone rivers and streams for a day or two. Flows are typically low everywhere throughout this period, and when the high country begins to freeze consistently every night, even freestone rivers like the Yellowstone that usually carry a hint of color turn clear as glass. Water temperatures now drop into the 50s everywhere, with 40s possible on cold mornings on smaller streams.

No later than September 20 and often earlier, these dropping temperatures begin to push hatches and fish activity towards midday and the afternoon. Morning fishing becomes limited to streamer and nymph fishing for the brown trout beginning their spawning runs, which don’t like bright sun. These dropping temperatures (as well as the less-consistent weather) are universally good for larger rivers, geyser-heated waters, and spring creeks. They’re not good for small mountain streams. Small streams only remain fishable until the first cold snap. After that, they’re usually too cold for the remainder of the season, and even larger freestone streams like the Lamar Drainage in Yellowstone Park will become challenging during cold spells.

Top Fisheries

The top fisheries in early fall can include every fishery in the region with the exception of small creeks. With the exception of extremely hot or cold weather, all other fisheries should fish acceptably well throughout the period. This is one reason why early fall is a great period for anglers who wish to fish a variety of waters. When the weather runs to one extreme or the other, the quality fisheries will likewise slant one direction or the other.

Cold and wet weather will make large rivers, streams that host brown trout spawning runs, geothermally-influenced waters, and lower elevation waters in general fish better than others. Hotter, drier weather will make freestone streams within Yellowstone Park (the Lamar) and the Yellowstone River fish better than other options, and warm-dry weather is really your only chance if you do wish to fish small mountain streams. Ideal weather for fall fishing consists of temperatures in the 50s with cloud cover. Such conditions will make everything except the little creeks red hot.

The Stillwater River is a bit of an outlier here. This small river at low elevation often gets too low to float in early September. It needs either a heavy snowpack year or rains in September to stay above the 475cfs level below which even small rafts struggle to avoid running aground, though too much rain can blow it out.

While small high-elevation lakes are typically not good choices in early fall, low-elevation ranch ponds begin to kick into gear once weather cools, and lakes that hold brown trout will see these fish gathering in inlet areas in preparation for the spawn. Hebgen Lake just west of the Yellowstone Park boundary is the most-famous example.

My favorite early fall fisheries in Yellowstone Park are the Gardner River, for early fall-run browns, and the Yellowstone River. On the Yellowstone, the hike-in streamer fishing is excellent in the canyons, and BWO or hoppers usually bring rising fish in the afternoons, depending on whether it’s cold and gray or hot and bright.

When fly fishing Montana in early fall, my preferred fisheries are the Yellowstone River and the lower Stillwater River, if the latter remains high enough.

On the Yellowstone I like the entire river from Gardiner downstream past Big Timber, since the crowds are now gone and water temperatures are ideal. Since the crowds are lower at this time, larger fish are somewhat more eager to eat tiny dry flies than they are earlier in the season, and there’s usually still a few big hopper eats in the cards. It often makes sense to float a short section at this time of year and fish it very slowly, getting out to wade-fish good areas. Earlier in the season, this usually isn’t a great idea. In early fall it can produce great results for anglers who’d rather take things slow.

On the Stillwater, I tend to move faster since most guides fish slow in the fall. Fall fishing here is usually a mixed bag of BWO and Drake Mackeral mayflies hatching sporadically through the day, hoppers, and modest-sized streamers. Since the Stillwater holds fewer whitefish than the Yellowstone, we’ll often go hopper-dropper here in September, which tends to be a bit easier for most anglers than fishing two dries like we do on the Yellowstone.

Fly Fishing Montana in Early Fall Tactics

With a couple exceptions, tactics vary in early fall depending on the weather. I’ll cover the things that DON’T change first.

Targeting early fall-run browns first thing in the morning or late in the day, in both cases when the sun is not yet on the water, using large stonefly and attractor nymphs (smaller, rougher rivers and streams) and streamers (larger float rivers) can produce a handful of larger fish regardless of weather conditions at this time of year. This is usually not a numbers game and is not a good choice for rookies and novices.

Larger freestone streams and river typically see at least fragmentary Blue-winged Olive and other small or medium-sized mayfly hatches throughout this period around midday. When hatches are limited as they are during bright weather, attractor dry flies like Purple Haze Parachutes or Purple Hazy Cripples (one of my patterns, usually better than the parachute) work better than hatch-matching dries. When the weather is ugly and hatches are more intense, either fish a hatch-matching dry and one of the purple bugs together, or fish a larger and more visible hopper or attractor dry (or a larger mayfly pattern if larger mayflies are hatching) with either the hatch-matching dry or the purple fly.

When the weather is ugly, particularly ugly and cold, stick to larger rivers (freestone or other), spring creeks, or geothermally-influenced rivers. Larger rivers will all see mayfly hatches under such conditions, though tailwater rivers will typically see smaller Pseudo mayfly (tiny Blue-winged Olive) hatches rather than the full-sized Baetis BWO during this period. Larger freestone rivers (Yellowstone and Madison) see Tan Drake (Drake Mackeral) hatches in addition to BWO hatches during bad weather, and fragmentary hatches of other larger mayflies (Western Cahill, Mahogany) may also occur during bad weather in the last few days of August through early October. Streamer fishing is also good on larger rivers. On spring creeks, look for midge or Pseudo hatches. On geothermal rivers, most particularly the Firehole, the White Miller caddis common in June are important now as well. There may be some mayfly hatches but these are more important later in the fall. Ugly weather is also a good time to focus on targeting browns and the occasional fall-run rainbow using big nymphs and streamers, even during the middle of the day.

When the weather is bright and sunny, freestone rivers may still produce fishable mayfly hatches (see note on BWO above). Terrestrials (hoppers and ants) can be expected to work on these rivers at least as well as mayflies when the weather is warm/sunny. Tailwaters may see midge or Trico hatches, but these are rare. Nymphing or perhaps terrestrials are better choices. Fishing will be challenging and usually limited to sight-nymphing on spring creeks, while geothermal rivers are probably not worth your time unless they hold fall-run browns (and then only early/late in the day). Smaller freestone rivers like the Lamar and Gardner continue to fish well on terrestrials at this time, though nymphing is probably a more consistent option now (whereas dry flies or dry/dropper were at least as good during summer). Hatches are more likely in the Lamar Drainage during bright weather than under gray skies in the fall provided temperatures are not over 70 degrees. These include assorted Green and Gray Drakes from size 10 all the way down to 16 (full size Green Drakes are larger, Flavs are smaller, the flies are identical except in size), BWO, black or cream midges, and Tan Drakes (Drake Mackeral). Even when afternoons are warm, the best hatch activity on all freestone streams and rivers is likely to occur around midday or even in the afternoon.

Who Should Consider Fly Fishing Montana in Early Fall

Early fall is a great time of year for any experienced angler provided they are willing to put up with larger than expected crowds in Yellowstone Park (particularly on roadside easy-access fisheries like the Lamar and its tributaries, the headwaters of the Madison, and the Firehole), are eager to fish for trout that are a bit spookier than they are earlier in the season, and are willing to visit fisheries and use tactics that make sense depending on weather and water conditions. It is a particularly good time for those who like Blue-winged Olive hatches, as this is prime time everywhere except spring creeks and tailwaters for these insects in Yellowstone Country. This is also a good period for anglers who want to spend some of their time hunting a handful of larger trout with nymphs and streamers but also want consistent fishing for numbers of trout part of the time. In general, fall offers slower-paced fishing but somewhat similar tactics than summer fishing.

Early fall is not such a great time for anglers who have specific fisheries or tactics in mind, whatever these may be, beginners, anglers who like small stream or alpine lake fishing (though larger and lower-elevation lakes are okay), anglers who come expecting low crowds without hiking, or anglers who like tailwaters but prefer to fish dry flies. It is also a poor time for anglers who prefer to fish in comfortable weather; sometimes early fall DOES see comfortable weather, but on most prime fisheries at this time, the better fishing is when the weather is cold and wet.