During the first part of the month of September you can expect water temperatures to start dropping into the preferred range for trout. The weather is usually very nice with cool, crisp mornings and warm afternoons. It may be 35 to 40 degrees in the early morning and in the seventies to low eighties in the afternoons, so be sure to dress in layers. During the month of September you have a choice of any stream you want to fish. They all will be within the ideal water temperature range. Stream that have been on the warm side like the Madison drainage will have cooled enough for good fly fishing opportunity and at the same time, the streams in the higher elevations are still warm enough for the trout to be active. It is also a beautiful time to fish with fall colors beginning to show up. Let’s begin with the Northeast corner of the park.
Lamar River, Slough Creek, and Soda Butte Creek
The Lamar Valley can be a little challenging due to low water but it will still can be a good choice. Some easy to access sections can be a little slow due to previous fishing pressure throughout the summer. A little and often short hike will put you in water that hasn’t been affected by a lot of activity. The insects that are hatching will begin to decrease some and terrestrials will become a little more important.
Yellowstone River
The Yellowstone can still be a very good choice because many think that it won’t have as many hatching insects and of course, it won’t in terms of sizes since the big stonefly hatch will have ended. There will still be plenty little Yellow stoneflies. Some sections of the river will still have some Flav or Small Western Green drake hatches taking place the first of the month. The river will have plenty other insects, especially the Blue Winged Olives, spotted sedge and little sister caddis and more terrestrial activity. Hoppers will still be active along with ants and beetles. There will be miles of the river that will have had little fishing pressure for those that want to put forth a little effort hiking.
Gardner River
The Gardner River always turns out a lot of fish during the month of September. All sections of the river will be in good shape including the lower part that was a little warm during August. Much of the river will have been ignored during the past month and fishing pressure won’t be a problem. You will see hatches of Blue Winged Olives, two or three species of caddis and some little Yellow stoneflies. There will still be a lot of terrestrial insects around as well.
The Fall River and Bechler River
The Southwestern section of the park will continue to be a good option. Probably the best thing going for the Fall and Bechler Rivers is the lack of fishing pressure. The cooler weather will have the trout in high gear and good numbers can be caught. You will have most sections of the river to yourself. Good hatches of mayflies and caddisflies will still be taking place.
The Snake River and Lewis River
The Southeaster corner of the park will be another good option. Again, these two rivers will have seen only a slight amount of fishing pressure. Both are good options for the first part of September. The Lewis river channel can turn out some very nice trout. Both rivers will have good hatches and terrestrials will also be important.
The Gallatin River and Grayling Creek
The Northwestern Section of the park will be yet another good option. Both streams will have received little fishing pressure during August and both will have good hatches taking place. Of course, terrestrial imitations will also be effective. These two streams usually produce a lot of action and very good numbers of fish. Both have several miles of water with very good access.
Madison River
The Madison River will have cooled down a little and a good bit by the middle of the month. There will be a lot of anglers anticipating the runs of fishing from Hebgen Lake but that mostly happens at the end of September and the firs of October. Good numbers of resident rainbows and brown trout will be caught throughout its entire length in the park. There will be good hatches of Blue-winged olives, some smaller Pale Morning duns at the first of September. Spotted sedge caddis, Little Sister caddis and White Miller caddis will be present. There will still be some little Yellow stoneflies hatching. Terrestrials including hoppers, ants and beetles will be the main focus of some trout.
Firehole River
Since the weather begins to cool, the Firehole will once again becomes a good choice for the fly angler. At the beginning of the month, it may only be cool enough to fish in the mornings. By the middle of September it should turn out good numbers of trout throughout the day. White Miller Caddis will be plentiful along with some Spotted Sedges. Blue Winged Olives will begin to hatch and some small Pale Morning duns will still be around the first of the month. Terrestrials will still be on the menu for the trout.
Fall fishing is truly one of our favorite windows for both Montana and Yellowstone National Park. Cool mornings and warm afternoons often produce the perfect blend of ideal water temperatures coupled with fall hatches and late season terrestrial fishing. The general family vacation season has slowed dramatically leaving the park to more serious anglers.