Late Summer Yellowstone Fishing Trips

Posted on January 24th, 2024 in Fishing Tips

angler, guide, and cutthroat trout

The Black Canyon of the Yellowstone remains a key hike-in destination on our August Yellowstone fishing trips. This fish ate a grasshopper.

Late summer, which begins in late July or early August and continues until the first cold nights in late August or early September (henceforth just called ‘August’), continues to offer excellent hike-in fishing, and both the hikes and the wading are usually not so onerous at this time as in early summer. In addition, this is prime time for small, rough mountain creeks that might still be too high in early summer. Regardless of locale, August Yellowstone fishing trips are excellent bets for anglers who like fishing terrestrial dry flies, and can turn out some big fish on subsurface flies, as well.

The downsides of late summer are continued crowds, especially on famous waters that flow through meadows, and potentially low, clear, and somewhat warm water than might mean we have to start fishing early in the morning and quit at midafternoon to avoid stressing the trout. The latter issue is much more common during drought years.

More wade-fishing options also up outside Yellowstone Park. While stretches of the Yellowstone River that don’t see much boat traffic remain our bread and butter option, lower flows also make it possible to wade several small streams safely (and legally), and the Boulder River is now too low to float, opening it up for wading anglers. While a bit out of the way, these options also enjoy less traffic than easy-access waters in the park.

mountain creek in Montana

Several Montana creeks provide changes of pace to Yellowstone Park in August. No, I won’t name this stream online.

Late Summer Yellowstone Fishing Trips: Quick Facts

  • Best Waters: Deeper, more turbulent rivers and streams are usually best in late summer: The Yellowstone, Gardner, rough portions of the Lamar River and Slough Creek, and many shady, rocky mountain creeks are top choices.
  • Three Top Reasons to Come in Late Summer: 1.) Excellent attractor and terrestrial dry fly fishing is common on most waters. 2.) Wading is much easier than it is earlier in the year. 3.) We typically see more large fish in late summer versus early summer.
  • Three Top Reasons to Avoid Late Summer: 1.) The fishing is less consistent than early summer, particularly during drought years. 2.) There are fewer insect hatches at this time than earlier or later in the season, so we fish attractor and terrestrial dries, nymphs, and streamers more than we match hatches. 3.) While not as crowded overall as early summer, the park and its waters are still pretty busy.
  • Perfect Clients: Late summer is ideal for adventurous, fit anglers who enjoy fishing steep, rugged rivers and streams, whether they’re looking for numbers of smaller trout on dry flies or big ones on nymphs and streamers.
  • What Late Summer Does Best: Produces good action for medium-sized fish with attractor and terrestrial dry-dropper combinations, while providing some opportunities for large fish on nymphs and streamers.

August Trips: The Details

Beginning in the last few days of July, the fishing in Yellowstone Park begins to shift to terrestrial insects. On steeper and broken streams that see lower pressure, this generally means grasshopper and cricket imitations. On streams with gentle gradients where pressure is heavier, it generally means ant and beetle imitations, while certain streams and the Gallatin River can see phenomenal falls of spruce budworm moths that really get the trout excited.

Aquatic insect hatches fall off in August, though we’ll occasionally see sparse mayfly hatches. These hatches are most likely when the weather is gray.

small creek waterfall

Small, cold, mountain creeks provide excellent fishing on hot August afternoons, as well as a few surprises. When I first explored this creek in the northeast part of the park, I didn’t know about this waterfall.

Speaking of gray weather, it’s not uncommon to have a few cold, rainy days in August, especially in the latter half of the month, though the average weather is still warm and sunny. We actually like cold days in August, because they reduce water temperatures and the forest fire danger.

Other than slight changes in the flies we use and the venues we fish, there are fewer changes with the transition to late summer on Yellowstone Park trips than on other guided trips.

The Yellowstone in its canyons remains our favorite destination for walk trips. Portions of Slough Creek, the Lamar, and the Gardner the main big-water support acts for experienced anglers. For experienced anglers who love small stream fishing, steep mountain creeks are usually better than gentle creeks on August Yellowstone fishing trips, both because the steep creeks may just be getting low enough to be prime by this point and because they are usually deeper, colder, and better oxygenated.

Angler streamer fishing the Yellowstone River

Angler fishing a streamer in a deep hole in the Grand Canyon of the Yellowstone River in late summer. The spot where he’s standing is inaccessible in early summer.

Deep, cold, and well-oxygenated water can be critical in late summer, especially in early August when the nights are still warm and the days still blazing hot. In drought years, water temperatures can be too warm in late afternoon. This is most common on shallow waters at low elevation, such as the lower Gardner River and the Yellowstone just before it exits the park.

When we run into warm water issues, we’ll either need to start fishing extremely early in the morning and quit at midafternoon or head to the high country to fish a small stream once bigger rivers get too warm for ethical (to say nothing of productive) fishing.

Beginner fishing on small brook trout streams remains good in late summer, though often we’ll fish steeper and faster streams and small rivers than we do earlier in the summer, for the same reasons just noted. By about August 20, the brook trout fishing falls off sharply and our beginner brookie family trips stop making much sense. In fact, after about August 20 most beginner anglers actually catch more fish on float trips than they do on Yellowstone Park hike and wade trips.

late August brown trout

Some big early morning trout are possible in late August.

Our focus often shifts on late August Yellowstone fishing trips, just as the weather starts shifting towards fall. Gray weather often prompts the first hatches of fall aquatic insects, the Blue-winged Olives and Tan Drakes. Gray weather and especially a few cold nights also increase our chances of catching larger trout on nymphs and streamers, especially for anglers willing to get out on the water before dawn to be in position and ready to make our first casts right at dawn when it’s legal to start fishing.

Otherwise, late August continues to fish like early August. Late August is therefore a bit of a changeover period: sometimes it fishes as described above, while sometimes we’ll want to go into “early fall” mode, at least for the first couple hours we’re fishing.

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