It’s hard to believe that summer is almost gone. It was a warm one, that’s for sure but fishing held up quite nicely in spite of the hot weather. The autumnal equinox will arrive on September 22 signaling the first day of autumn. Temperatures have been above normal throughout much of the summer but the weather has trended to more normal temperatures in recent days. Our light snow pack last winter along with the dry summer dictated that the Island Park Reservoir would be completely drained by now. Thankfully due to conservation by the Fremont Madison Irrigation District, creative management by the Bureau of Reclamation and thoughtful negotiation by the Henry’s Fork Foundation the reservoir now stands at almost 30% of capacity. Rather than facing fowl water from the bowels of the reservoir anglers have enjoyed clear, clean water throughout late August and September.
Upper Henry’s Fork
The flow in Henry’s Lake Outlet has been reduced to help store irrigation water in Henrys Lake. With low water many of the larger trout drop down into the Upper Henry’s Fork. Large trout are also moving up from Island Park Reservoir. Coffee Pot Rapids below Mack’s Inn and the Henry’s Fork above always produce some very respectable trout in the fall. As long as the weather is warm you should use a hopper with a bead head nymph dropper. Later on use a double nymph system with an indicator. Streamers and buggers also produce, especially in the early morning and late evening hours.
The flow from the Island Park Dam is currently just over 700 cfs. I don’t expect this to continue for more than a few days. With reduced irrigation demand the flow will drop significantly over the next couple of weeks. Eventually the autumn flow will be near 100 cfs. Floating the Box will not only be difficult if not impossible but also unproductive. There is good wading access through the 2-1/2 section of the Box Canyon. Smaller nymphs are very productive when the water is low. We recommend size 18 Zebra Nymphs, Flashback Pheasant Tail TB, Cocktail, Two Bit Hooker, and Skinny Nelson. Streamers and buggers are also very productive, especially in the morning and evening hours.
Last Chance / Harriman Park
Mahogany Duns have finally started showing up in strong numbers. I count these slender dark mayflies among my favorite aquatic hatches. They normally appear in the mid-morning hours but you will encounter them throughout the day if the weather is cool and cloudy. You’ll need emergers, cripples and dun imitations. My favorites include Mahogany CDC Emerger, Limestone Cripple, Mahogany Dun Split Flag, Mahogany Sparkle Dun, and Slate / Tan Nohackle in size 16 or 18. You can also expect to see good numbers of small Blue Winged Olive mayflies in size 20 – 22. These hatches will intensify as September fades into October. Other aquatic insects including Tricos, Callibaetis and slow water caddis along with terrestrials remain important considerations throughout September.
Wood Road #16 – Pinehaven
This water receives intense pressure throughout the summer due to easy access, strong hatches and large trout. This combination makes for very challenging angling. Fishing pressure will likely subside during the weeks ahead making Wood Road #16 a good choice for large rising trout. Don’t expect these trout to be any easier to catch. You’ll need the right pattern (same as described for the Ranch) and perfect drag-free presentation, and a good dose of good luck.
With lower stream flows the fast water in the canyon becomes a little more user friendly. Use the same patterns described for the Box Canyon. There is good wading access at Riverside Campground and Hatchery Ford (FS #351.) If you are a little more adventuresome you can hike down into the canyon from some of the trails including Sheep Falls (FS #163) and Wood Road #6 (FS #151). Hoppers are very prolific in this section of the river making a hopper/dropper a good bet for hot action.
Warm River to Ashton
The section from the Stone Bridge below Warm River downstream to the county boat dock below Highway 20 is one of top choices for our guides. There are plenty of cookie-cutter 10 inch rainbows as well as larger Rainbow and Brown Trout. There is good wading access in the upper and lower stretch. We recommend using the same patterns described for the Box Canyon.
Ashton Dam to St Anthony
We normally don’t recommend the water from Ashton downstream during the hot summer months. Now that we are into mid-September it is time! There has been a lot of drifting aquatic vegetation making nymph and streamer fishing very difficult and almost impossible to land large trout. This will quickly change as the temperature drops at night and the stream flow is reduced. Dry fly fishing should pick up later in September. For now your best bet is to stick with nymphs and streamers. The morning hours have produced good dry fly fishing with Tricos at the Fun Farm.
St Anthony to Confluence
Trico fishing has been good in the morning hours. Later on try hoppers with a nymph dropper. Things slow down in the afternoon hours when the weather gets hot. As we move further into autumn and the weather continues to cool the fishing will improve. Cooler weather will also decrease the bothersome drifting vegetation.
Henry’s Fork Tributaries
As always, Warm River and the Buffalo provide great fishing for small trout throughout the heat of the summer. Both streams are spring creeks that remain cool enough to keep trout active. Lower Fall River was quite low throughout the summer but that has changed. Fall River is an excellent choice for quality fishing with light angling pressure. Most of the water in the lower river flows through private land. Make sure you have permission if you plan to cross private land to get to the river.
Hoppers and ants are still working well. I like to use a hopper with a small black ant as a dropper about a foot below the hopper. Mayfly hatches have been a little inconsistent but that will likely change later in September. The Madison always gets good hatches of Blue Winged Olive mayflies. Look for feeding fish in the slicks. Until the mayflies get going your best bet is to use small nymphs like Zebra, Pheasant Tail, Two Bit Hooker and Electric Caddis. Streamers have also been very productive for larger browns.
Henry’s Lake is on. Best fishing has been in the morning hours from daylight until mid-day. Use a slow sinking or intermediate line with small leeches or wooly buggers. You can also use a high floating dry fly with a small nymph dropper. The same techniques work on the other area lakes. Island Park Reservoir is getting low and the trout are starting to concentrate near the springs.
South Fork of the Snake
The stream flow on the South Fork is below normal for this time of year and it will continue to drop during the days ahead because Palisades Reservoir is only 5% of capacity. The good news is that the water is still clean and clear. It can get dirty fast if we get a lot of rain. There have been good hatches of Mahogany Duns and Pink Alberts in the riffles.
Yellowstone National Park
There isn’t a better time to be in Yellowstone Park than late September and October. The water temperature is cool, the trout are moving, aquatic insects are emerging, and the elk are bugling. Virtually all of the waters within the park are worth fishing. Look for the Firehole to wake up with cooler water temperatures. Trout are beginning to move into the Madison River to make their fall spawning run up the river. Large Cutthroat trout in the Yellowstone River are actively feeding. Some of the best mayfly hatches of the season occur in the Lamar River and Slough Creek.