River conditions here in Montana are always changing. During the spring, our high mountain streams transport the snow melt into the larger rivers. This causes a "blow out" period that can last a month or more, making fishing dangerous and sometimes impossible. The period after the spring run-off can be excellent angling however. The trout are hungry after hunkering down while the rivers raged. Summer brings low water, as much of it is used for irrigating crops and the snow-pack running thin. In the winter, water levels continue to drop, making for concentrated pockets of fish. Knowing where the fish are during these periods is critical. During the heavy flows, fish get pushed to the edges of rivers where the current is less resistant. In winter, the low, clear water forces fish into deep calm pools where they can escape from the raptors above. Its a never ending game of change and pursuit, here's my two cents on finding trout year round.
They say the ideal current speed is around three miles per hour. Foam bubbles are a key identifier of current speed. You'll notice faster water and slower water just don't carry bubbles on the surface. On the outside of a feeding lane the water is rushing fast, but inches next to it, where current meets slower water, bubbles form. The fish love this speed. It gives them enough time to identify and eat insects as they drift down stream plus they can efficiently hold themselves without using too much energy. Remember to always look for the right current speed, this is where the majority of trout lay. We have endless miles of rivers in Montana, so it can be intimidating trying to find where the trout are. I often walk a quarter mile or more between good trout lies. Not all water holds active fish. Get it in your head to remember what the current speed was after each fish is caught and it wont be long before you can easily identify good trout water. I'm not saying that fish aren't in fast riffles because they are, particularly rainbows. You just have to get out there and experiment with what works. I've seen people fishing holes that have nothing in common with trout water. Its too shallow, muddy bottom, not significant enough, or just the wrong time of the year. Don't be that guy wasting your time on water that holds zero fish.
Just because the rivers are blown out doesn't mean you cant fish. Yes, some rivers get very dangerous but others, for example Hyalite Creek, is still great even when its raging. Finding fish in these waters can be much easier than say, during the middle of summer. During summer the whole river looks decent and fish are so spread out. When rivers are near maximum capacity, still within the banks, fish are concentrated in the slowest moving water. Hyalite Creek is a steep mountain stream with class IV rapids at places. The other day I drove many miles looking for anything other than whitewater. When I found a bend where the river flattened out and slowed down, I also found a ton of trout. One particular stretch I walked had nothing but whitewater, but near the bank there was a small pocket of calmer water. I fished this until I caught three brookies. How easy was it for me to find these fish? Very easy! Making my way downstream I found a gorgeous body of water familiar to every fly fisherman. I could have easily fished this hole for three hours without leaving, and I did. Its so simple, like I said before, the fish are now concentrated in these slow moving stretches.
I would like to talk about water clarity for a moment, it has a lot to do with where the trout will be feeding. Most people pack up and go home if the river is muddy and visibility is low. They believe the trout wont see their flies and they'll have to put it on the tips of their noses. Well this just isn't true. Obviously if conditions are chocolate milk, and you cant see your hand an inch below the surface, yes its time to probably go home. Around here though, many rivers never turn to chocolate milk. I personally love fishing when the river is slightly high and cloudy, maybe a bit green. It makes the fish feel protected from raptors and other predators. A typical cycle in the summer tends to be on bright cloudless days the big trout hold deep, away from the sunlight. At twilight they feel comfortable to come out and feed. This is the same during cloudy conditions. The trout feel comfortable spending the entire day, even if its bright and sunny, feeding. Also, as fan of the art of high-sticking, I can get much closer without being seen.
With that being said, I'm going to move into finding the trout during the summer months. It can get blazing hot outside. Just as you wouldn't want to fish below thirty degrees (the fish slow down), It's not the best time to fish when its one hundred degrees. The fish get lethargic as the water temp rises, making them more active at night and twilight. Shallow water is a no-go during the dog days of summer. The fish are deep, often avoiding the warm rays of sunlight. Its a good idea to try the riffles this time of year, many rainbows will be found there. Deep and slow runs, fished with just about any fly works great. Hot days usually means low water, so fish are concentrated within the confines of the river channel. When its hot and there's no cloud cover above, try to focus on the deep holes within the river system. There are often long stretches of shallow, clear water that hold no fish. Its easy to recognize these spots, walk a little further upriver, and you'll eventually come upon a deep hole. Its here that the smart trout will spend their days, hunkered down deep, chasing down nymphs and sculpins that enter their feeding zones. It can often be difficult to reach these fish with the traditional nymph set-up. Use a longer leader, 12 to 15 feet, tapered to 5x tippet, and weighted flies. If you're flies arent heavy enough, simply put on a split-shot or two. Remember, you want to be on the bottom. If you're not detecting the bottom then you need to change your approach so that you are down where the fish are. If fishing during peak daytime hours this should have you covered. Its during low light that your technique should change from the above mentioned during summer months. In low light times, its the lunker brown trout and pig rainbows that move out of the cover of deep water and into ambush mode in the shallows. Its no surprise that big trout are naturally nocturnal. Pack a headlamp and begin your outing an hour before dark. Use large flies like black sculpzillas, mice patterns, crankbaits, etc. Night fishing can be a challenge within itself but is often one of the best times to be on the river. Theres nothing like casting dries to rising fish during a full moon either!
Fall is one of the best times to fish, if not THE best season. The brown trout have spawning on their minds, along with all fish trying to stock up for the coming winter. Water levels remain low and its still easy to find the fish if you know how to read the water. During the fall you can fish in pretty shallow waters, all day. The photo period is shortening and trout are taking advantage of the cool temps and low light. Large browns will ambush small fish all day long and the usual riffles and holes will produce hungry fish eager to eat your flies. Its during fall that you can throw larger than usual streamers, larger than real life insect patterns, and that crazy Bozangles Betty that you tied a couple of years ago. The feed is on and trout tend to get out of their comfort zones in order to secure a high calorie meal, take advantage of this. Trout will be found in any and all stretches of rivers and lakes during the fall, so find some fishy structure, tie on the right flies or lure and enjoy the action. Keep in mind that egg patterns go hand in hand with early spring and fall. Brown and rainbow trout cant resist the high calorie morsel and will cross water to reach them.
Where are the trout during the coldest months of winter? You may be the type that puts down the fishing gear when winter arrives and dust off the ski equipment. But, there are still excellent opportunities to fish year round in Montana. Winter can be one of the most beautiful, solitary, and calming time of the year to fish. There's just nothing quiet like fly fishing in the middle of winter on a beautiful sunny day. The fishing can be pretty phenomenal if you have some insight and a little bit of luck. Fish get pretty lethargic during the cold temps of winter. They are less eager to viciously track down a streamer over larger distances and typically stay in a narrow feeding lane, letting the food float to them. Its easy enough to find fish during the winter. During real cold, sunny days, the trout will stack up in the big pools, similar to summer holding patterns. Its during the warmer, overcast days that you can find fish moving out of those holes and into shallow riffles and runs. Small nymphs like #18 pheasant tails, #16-18 lightning bugs, similar sizes disco midges, zebra midges, WD-40s, etc should be fished on light tackle. I use 5x in the winter because visibility tends to be crystal clear, along with lethargic energy levels from trout, thicker tipper is not necessary unless throwing streamer patterns. The winter time can host some pretty spectacular dry fly hatches. Its a midge game so having on hand some small Griffiths Gnats or #18-22 Parachute Adams is ideal. Keep your setup light and simple during the winter, find those winter holding areas and you'll be skipping a ski day at Bridger to head out to your favorite honey hole, and the best part is you will likely have the river to yourself.
As mentioned above, spring can bring a halt to the fishing in all but a few places in SW Montana. This period is known as the blow out and happens every year, some better than others. This causes the rivers to swell to dangerous proportions, creating low visibility and unfishable currents. After the blowout subsides however, and the fishing picks up pretty good. After a long winter of low angling pressure, than a month or so of zero angling pressure, post blow out means the fish are feeding heavily for the first time since last fall. The rainbows are beginning to think about the spawn and all fish are putting on the calories that were lost while holding over during the winter. As soon as the rivers clear and lake levels settle, one needs to hit the water. Trout will be in all stretches of the rivers now and finding them is relatively easy. Just fish those pools, runs, and riffles with the usual flies it wont be long before you're netting fish. Fly choice is more important during the spring than where you fish. San Juan Worms and spring run-off go hand in hand. Fish are more aggressive during this time of year, a lot like the fall, and will go out of their way to eat your fly. Dry fly fishing can be spotty, as this time of year is known for the higher than usual flows and stained water, which doesn't really have fish looking up. High calorie items just as eggs, worms, leeches, bait fish, salmonfly nymphs, etc will work best. Don't be afraid to use some extra weight to get those flies down deep, and be sure to bring plenty of extras to compensate for more debris floating downstream.