By mid April the baetis will get started. This is a very heavy hatch and in the late afternoon to evening you can expect to see pods of fish rising to baetis and midges. The baetis hatch will last well into May.
The fly fishing season basically gets going on the Big Horn when the weather breaks and we get a warm spell sometime in March. On warm, sunny afternoons you can expect to see fish rising regularly to midges. The streamer fishing can also be exciting in the early spring. This is Montana, so the weather can change drastically in a matter of hours. Be ready for 60 degrees one day and a snowstorm the next.
Sometime from the end of May or early June the runoff happens. Since the Horn is a tail water the run off has a very small impact on the river. The flows may increase some, but the fishing will not suffer from it.
In June the baetis will taper off and the pmd's will begin to emerge. There is some real optimism that the recent years of high water may help bring the pmd hatch back to the levels of past seasons.
As we move through July two really major events come into play. First the black caddis will begin to emerge. This hatch is incredibly intense and can bring pods of fish to the surface.
August and September also brings out some tricos. While this hatch is no where near the intensity that it once was you can still find fish sipping spinners in places in the morning. If you want to target trico sippers get out early, before 8 am, and carefully scan the river for gentle rise forms. Stalking these early morning trico sippers is some of the most challenging fly fishing on the Big Horn.
The fall in Montana is a magical time. The hot days of August are gone, the crowds begin to thin, the leaves turn to a brilliant gold and the pheasants are making themselves known all along the river. The early fall brings out the small baetis, which many still call by their old name, pseudos. These are tiny, size 22 or 24, so be ready to fish small flies and long, fine leaders.
The further we go into the fall the more aggressive the browns become. If you love to throw big streamers to big browns this is the time to be on the Big Horn. This is not just a time for browns though. There are plenty of rainbows willing to whack streamers in the fall. This is especially true on the lower river.
There is one constant that will produce fish just about every single day of the year on the Big Horn. That is nymphing. The hatches will come and go, but the Big Horn has such a rich biomass of insects and invertebrates that the fish always have an incredible amount of food available to them
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The Big Horn has many hatches that bring the fish to the surface, but day in and day out most of the time nymph fishing will produce fish for you.
Sometime after mid July the fish begin to crave the countless grasshoppers that line the banks of the river. The emerging caddis have the trout looking up for a meal. Then, when the natural hoppers begin to hit the water these two insects in combination make floating a hopper pattern down the river an explosive experience!
