Quick answer: Ask the people who fish Missoula for a living when they take their own days off, and a lot of them say September. Early in the month it still feels like summer, with big hoppers along the banks. Then the first real fall rains, often around September 10, cool everything down, and the whole complexion of the fishing changes: tricos give way to blue winged olives, mahoganies start mid-month, and the big October caddis show at the end. The water hits prime temperatures, the wading is the most comfortable of the year, the crowds are gone, and the bigger fish start feeding harder as the nights cool.

Peak dry fly fishing in Missoula runs right through September. Here is what a September guided trip looks like.

How does early September differ from late September?

Early September is summer with better manners. The hoppers have been growing all summer and they are big now, but by September the fish have seen a lot of them, so your guide carries a range of hopper sizes and patterns and changes them until one gets eaten. Ants and beetles still move fish. Mornings are cooler, afternoons are warm, and the rivers are low and clear.

Then the rains come, usually around the tenth, and the month turns. Air and water temperatures drop, the bugs change, and the trout shift from summer patterns to fall ones. From mid-September on, the bugs range from size 6 hoppers to size 22 olives on the same day, which is why your guide’s fly box gets interesting.

What is hatching in September?

Hoppers early in the month, still the main event on warm afternoons.
Tricos in the mornings early on, then fading as the weather cools.
Blue winged olives, which replace the tricos as the main hatch after the first rains and come off best on cool, cloudy afternoons. Once the olives are on, fish can see color and will refuse the wrong fly, so this is a month for a careful guide.
Mahoganies, starting mid-month and running about three weeks.
Hecubas, the big fall mayfly, on the rainy, cloudy, drizzly days.
October caddis, the big fall caddis, at the very end of the month, especially on the lower elevation rivers.

And a rule your guide lives by in September: if the fish are not eating on the surface, they are eating underneath. Slow surface days are often very good nymphing days.

What are the rivers like in September?

Prime. The water is at comfortable temperatures with longer, cooler nights, the flows are low and clear, and it is the most comfortable wading of the year. The Bitterroot fishes especially well at these lower flows, and the Clark Fork starts building toward its fall peak. As the water cools, the bigger trout start feeding harder, and the fishing takes on a heavier, more deliberate feel than the dog days of August.

What is a September day like?

Comfortable. Cool mornings and evenings, pleasant days, and the first fall color coming into the valley. Starts are later than August, since there is no heat to beat. A typical day might be hoppers along the banks on a sunny afternoon, or an olive hatch and steady risers on a gray one, and your guide reads which day it is by mid-morning. Bring layers, because a September day can start cold and warm into shirtsleeves. Most people are still wet wading early in the month and back in waders by the end of it.

Why fish September with a guide?

Because September is a month of transition, and the fishing changes with the weather week to week. A warm, sunny afternoon calls for hoppers, while a cool, gray one might mean a blue winged olive hatch and rising fish that will refuse anything but the right size and color. Your guide reads the day and adjusts, and knows which rivers are cooling into prime shape and which are winding down. You pick your dates, and we put you on the water that is fishing best.

Common questions about September in Missoula

Is September really better than July? For a lot of locals, yes: fewer people, cooler weather, comfortable wading, and excellent fishing. July has more bugs on the water. September has more room.

Will the fishing be slower after the rains? No, it changes. The first cool weather often turns the bigger fish on. It is why the last week of September leads into the best two weeks of October.

Do I need waders in September? Early in the month, no, wet wading is comfortable. By late September the mornings are cold enough that waders are nice. We can lend a pair if you do not own one, or you can rent from Rent Waders (rentwaders.com), a Missoula company that delivers to our shop. See What to Wear.

Is September crowded? No. The summer crowds thin out, and weekdays are especially quiet.

How far ahead should I book? Six to eight weeks if you can. September is popular with people in the know, and the late-September window is short.