Introduction to Fly Fishing Montana in Late Summer

Fly fishing Montana in late summer continues trends started in early summer. During this period that runs from late July or early August through the first run of cold nights in late August or early September, the weather is generally still nice, the water continues to drop, and the trout continue to look up for dry flies.

Overall the crowds of anglers and tourists are slightly smaller by early August than they are in July, and get a lot smaller by August 20 except in Yellowstone Park. The fishing is usually still consistent, though it is not so easy as it is in July. Except during exceptionally low water years, the trout get in better and better shape as summer progresses, and get prettier due to clearer water. The first hints of fall are in the air, particularly in late August and just before Labor Day, showing in the dry grass, the hints of autumn color in the undergrowth, in the first fall Blue-winged Olive hatches, and in the brown trout starting to become aggressive in preparation for the spawn.

With the exception of early summer, late summer is the most popular season in the region. It’s better for anglers who don’t like crowds. It’s worse for beginners. It’s better for anglers who like fishing terrestrial dry flies. It’s worse for match the hatch fanatics. The biting bugs are certainly less annoying at this time, and the streambanks are now dry and firm, since runoff is definitively over, but there’s always the chance for wildfires and late afternoon fishing can be questionable when the weather is hot, due to high water temperatures.

Weather and Water Conditions when Fly Fishing Montana in Late Summer

Late summer weather is slightly less consistent than early summer weather. While daytime highs are usually still in the 60s to 90s at all elevations, (70s to 90s most common) nights begin cooling into the 40s and 50s, particularly by about August 20, and some frost is possible in Yellowstone Park. Storms, particularly those associated with early cold fronts, are more common though are still rare. In Yellowstone Park and nearby locations, a significant cold front comes through at some point in the latter half of August about one year in three, bringing snow to the highest mountains and temperatures that don’t break the low 50s even at low elevations. While rare, when fly fishing Montana in late summer you should come prepared for this eventuality.

Water conditions are highly variable in late summer and primarily depend on how cold and wet the previous winter and spring were. Flows are always lower at this time than earlier. The question is simply whether they get low enough to cause problems, or merely decline.

If not much snow fell and/or it melted early, late summer sees low water and warm water temperatures. These conditions can lead to poor late afternoon fishing and/or unethical fishing conditions if water temperatures crack 70 degrees. Some waters including the Lower Madison regularly see afternoon closures at this time due to low/warm flows, which stress trout. These problems are most acute in early August in drought years. Except on the Lower Madison, any restrictions in the Yellowstone area are usually lifted by August 20, due to cooler nights. Note that points further west in Montana, at lower elevations, see much more widespread closures.

When the previous winter was normal to wet, or what snow that did stick melted very late, flows remain high enough that there are no temperature issues and late summer water conditions are actually better than they are in early summer.

Another potential problem in late summer is weed growth. While most common on the Missouri, other large, low-elevation rivers also see substantial weed growth, particularly in dry, hot summers. These weeds make nymph fishing more troublesome though do not generally impact dry fly fishing.

Smaller mountain streams and waters within Yellowstone Park itself (with the exception of the geyser-heated headwaters of the Madison, including the Firehole and Gibbon Rivers) do not see the above problems. Rougher mountain streams and rough rivers like the Yellowstone are usually easier to fish in late summer than earlier. I stress “to fish” because the “catching” is usually somewhat more challenging at this time, as the fish get spookier as the water drops and the insect hatches decline; it’s just the wading and walking the banks that get easier.

Top Fisheries

Fly fishing Montana in late summer centers on the Yellowstone River drainage, since this is the highest-elevation and coldest drainage in the region. All waters in this drainage both inside and outside the park continue to fish well during this period, with only the lower Yellowstone downstream of Livingston sometimes seeing water temperature issues during the hottest and driest summers. The Boulder River gets too low to float by late July, but it is still a good wade fishery, especially for non-guided anglers who head to its headwaters and guided/non-guided anglers visiting its forks.

Other good fisheries including those beyond our operations area include the Madison River between Hebgen Lake and Ennis Lake, the Gallatin River upstream of Four Corners, and the Missouri River. Anglers who like fishing small mountain creeks will love late summer, both inside and outside the park, though the smallest meadow creeks often run too low. Stick to the steep, fast creeks full of boulders.

As noted above, warm water temperatures are a problem at this time. High flows alleviate these problems on all waters. Low flows make them worse. The streams that always or almost always see problems and as such are not worthwhile (or sometimes even close) at this time are the Firehole River, Gibbon River, and Madison Rivers inside Yellowstone Park, the Lower Madison River downstream of Ennis Dam (which now always faces mandatory 2:00 closures between July 15 and August 15), the Gallatin River and its tributary the East Gallatin downstream of Four Corners, the Gardner River downstream of its hot spring Boiling River, and the Yellowstone downstream of US Highway 89, east of Livingston Montana. These are listed in order from “are always too warm” to “least likely to be too warm.” Other waters are very unlikely to be too warm.

One “niche” fishery worth noting in late summer is the upper Missouri River from Three Forks, Montana downstream to Canyon Ferry Reservoir. While only a marginal trout river in this section (upstream of its famous tailwaters), this stretch of the “MO” is home to vast numbers of big carp. In late summer, it’s possible to sight-fish for these bruisers in shallow water. This is suitable only for advanced anglers, but it can be EXCEPTIONAL if you like carp. They typically run 4 to 10 pounds and you’re unlikely to have much competition besides local guides like me chasing these fish on their days off.

My favorite fisheries for walk-wade fishing in late summer are the Yellowstone River in its canyons, from the Lower Falls down to the point where the river exits the park at Gardiner, portions of the Gardner River, and assorted small mountain streams outside the park. For floats, I prefer the Stillwater River and the first 30 miles of the Yellowstone north of the park, basically from Gardiner to Emigrant, over points downstream. The higher the water and the cooler the weather, the more I like points further downstream as well. In fact, in wet years with good hopper populations, lower Paradise Valley and points east of Livingston are just as good as the upstream areas just mentioned.

Fishing Tactics

The dry fly fishing remains strong in late summer, but it’s less consistent than earlier save on small mountain creeks. Insect hatches are more fragmentary and the water is simply lower, slower, and clearer than it is earlier in summer, so the fish are somewhat spookier. The top dry fly bite in late summer is on terrestrial insect imitations. Imitations of ants and beetles will bring more strikes on most waters than larger flies, but grasshoppers and crickets are far more popular among anglers.

I typically have my clients fish a small grasshopper with an ant dropper at this time; it’s usually my best rig overall in late summer, both for numbers of fish (on the ant) and bigger fish (on the hopper). Large hoppers with nymph droppers can also work well, particularly on larger, rougher sections of river.

In regard to hatches, mayfly imitations are generally more effective than for the remainder of the season than caddis, since most caddis hatches conclude by the end of July or early August. Mayflies are usually small: Tricos on spring creeks and tailwaters, the smallest Green Drakes (#16) in the Lamar Drainage, and the earliest fall Blue-winged Olives by about August 20 on most rivers. Hatches of all these insects are usually fragmentary, but mayfly nymphs will work anywhere at this time. Stoneflies are usually limited to the Nocturnal or Midnight Stone present on freestone rivers, which can be matched by large tan-gold grasshopper imitations.

One more note about flies & hatches: during EXCEPTIONALLY high water years, most recently 2011, all early summer conditions can continue until as late as August 20. Check with me, or any area shop or outfitter, prior to your trip to see if this is the case. These conditions lead to great fishing and far stupider fish than you’ll usually find in late summer, they’re just not expected.

Pay close attention to weather forecasts in late summer. If it’s going to be cool and gray in the afternoons, you’ll want to be fishing at this time. If it’s going to be hot and cloudless, you’ll be better off getting on the water shortly after dawn and quitting when the sun is directly overhead. This is true regardless of water temperature.

When the weather is warm, expect to find the fish in fast water as they were earlier in the summer. Often the sudden drop-offs from shallow water to deep hold more fish than true shallow water at this time, since flows are slower, insect hatches are less intense, and the water is clearer. If early cold snaps have come, especially common late in this period, the fish will begin moving out of faster water to slightly slower areas with a fast walking pace, where they don’t have to work so hard to hold position. These areas will generally still be highly-oxygenated (turbulent or choppy), however.

As I noted in the weather and water conditions section, weeds can be a problem at this time. Check your flies regularly: trout don’t like salad on their steak.

Who Should Consider Fly Fishing Montana in Late Summer?

Fishing in late summer is generally suitable for the same anglers as fishing in early summer. The trout still like dries, all of the same waters are generally good, and the crowds of other anglers are almost as heavy until about August 20.

There are some categories of anglers for whom late summer is better. Anglers who are unsteady on their feet will find walking and wading all streams easier at this time, due to reduced flows and sturdier bottoms and stream banks now that the banks have dried out and the rivers dropped. Late summer is also better for high mountain backcountry anglers, since stream crossings are easier at this time and all waters have dropped from runoff even in the wettest years.

Anglers interest in match the hatch fishing can do as well in late summer as earlier, but they should expect to work harder for their trout since the insects are smaller and their hatches are more fragmented, and because the water is lower, slower, and clearer, so the fish are spookier. On the other hand, anglers who like terrestrials will do much better in late summer than earlier. Plenty of beginner options remain available in late summer, but the consistency of beginner fishing is not quite as good, again since the fish are a bit spookier.