When it comes to fly fishing there are limitless sizes, colors, shapes, and styles of flies to choose from. Fly patterns are as varied as the anglers that tie them. Understanding where to start when selecting trout flies for a day on the water comes down to research. Here’s how to get yourself on track when selecting flies for your next fly fishing adventure.
It was mid-November. I was traveling across country from Florida back to California at the end of the Canadian Football League season. I started by playing quarterback for the Miami Hooters of the Arena Football League that year and finished by playing quarterback for the Shreveport Pirates. Oddly enough that was a Canadian Football League team. There wasn’t any fly fishing near me in Shreveport save a small pond with bass and bluegill, and there was absolutely no trout fishing near me. I decided to make my cross-country journey into a fly fishing adventure once I hit the Colorado Rockies.
November in the Rockies can be cold and snowy. Growing up in California I never had to fish a river with snow on the banks. Most of our fisheries in the Golden State are tail waters and the majority of our temperatures range well above freezing. Fishing in this new environment was going to be an experience for me.
My plan was to fish the rivers around Vail. The Eagle, Taylor, Frying Pan, and potentially the Roaring Fork were all contenders. After early November snowfalls unseasonably warm weather set in and which melted much of the snowpack. This left the rivers high and muddy. Of the four rivers I wanted to fish the only one that was fishable was the Frying Pan. Figuring I might as well make the best of a bad situation I went to the local fly shop to get Intel on the Frying Pan River. Their suggestion was to fish fine and far off. Meaning size 18 or smaller flies and long leaders with fine tippet. The frying pan is a tailwater, so this made total sense. We talked for about 15 minutes and I purchased a dozen size 20 black pheasant tail nymphs at the shop owner’s urging.
When I hit the river I could see that the water had a little stain to it but it was still reasonably clear. So I tied up a 12 foot leader ending in 6x tippet. I attached the tiny pheasant tail and a zebra midge and went to work. I made several casts with no results trying pockets, seams, runs, and finally riffles. After about 20 minutes I decided to try different fly combination. I tied on a WD-40 and another tiny mayfly in olive. I made searching casts, diligent about working every piece of water thoroughly. And once again I got no results.
Frustrated, I took a break on the banks of the river and surveyed my fly box to see what options I had left. The shop owner was adamant that tiny mayflies were the ticket but I’d worked them pretty hard in places I knew fish should be to no result.
Resigned to giving this river everything I had, due in large part to the fact that there was no other option, I tied on a size 16 tan scud for my bottom bug and left the tiny pheasant tail for my top bug. The Frying Pan is a tailwater which has a good population of scuds. I suspected the warmer temperatures and rising water levels might make them more active. I stepped into a nice run just up from where I had been fishing before and proceeded to cast to likely holding water. My first couple cast got no results. Then I cast to the outside edge of a soft seam near the far bank. I saw the point where my indicator turned over as my split shot contacted the river bottom. About three seconds later I saw my indicator dunk. I set the hook and came tight to a 15-inch rainbow. It was the first of several that I caught on the day. Every one of them on the size 16 scud pattern. After that run up top I went back and fished the water where I had started with the smaller nymphs and made contact with fish in all the spots where they should be.
On the day I end up fishing for about six hours and landing about a dozen fish. Nothing breathtaking, my biggest fish was around 17 inches, but a productive day of fly fishing, nonetheless. Rising water levels and snowmelt changed the nature of the river that day which changed the pattern. Understanding how the changing conditions changed the river and finding the right fly pattern for those Frying Pan fish made the difference for me on that day and saved my first Colorado fishing experience.
With all of the information available online you should have a basic idea of the flies and hatches that work in the rivers you’ll be fly fishing. With that understanding you can move on to finding local knowledge.
More times than not fly shops know the general patterns that are working on their local waters. Their whole business is helping people catch fish. The better experience an anger has the more likely they are to become a repeat customer. Generally, the closer they are to the river the better the intel they’ll be able to collect. A fly shop sitting on the banks of a river is likely to get more frequent reports of what’s happening on the water. Proximity means they’ll have their finger on the pulse to what’s going on that river on that day. As a result, they’re way more likely to know the exact bugs that are coming off and steer you to the files that are working for their fly fishing customers. If the fly shop in your town is your only option that still a decent place to start but look for more specific knowledge if you can. Local guides local anglers and fish & game officers are all great resources.
Even if you choose a fly shop near your location conditions can change. Especially during spring and fall when fluctuating water levels can have a drastic effect on a river’s condition. My experience of the frying pan is a great example of that. Though the fish had been on that tiny PT prior to the melt off, warmer temperatures and rising water levels affected the river dynamics and changed the hatch. Even the best intel can change with big environmental changes. So leave yourself options.
Everybody wants to be there when the legendary hatches come off. The Salmonfly hatch on the South Fork is a great example. Too many times fly shops and anglers get caught in the romance of the big hatches that happen on major rivers. For years I had heard about the Hexegenia hatch on the Fall River. The fly shop owner that I talked to was so dialed into it that I ended up on the river with a ton of Hex nymphs and dry fly patterns. To my dismay, the Hexegenia didn’t really happen that year. I ended up with a bunch of huge mayfly patterns that rusted before I used them. I’ve had this experience several times, including the spruce moth on the Big Hole, October caddis on the McCloud and salmonflies in the box canyon of the Henry’s fork. It’s great to be ready if you hit the timing just right but make sure that you’re getting useful current Intel and not wishful thinking.
Think like a Boy Scout and always be prepared. You should have a good selection of bugs in your fly box to chosen from in several different flavors. Research in advance will help you narrow it down a bit. For instance, you’re never gonna throw a Salmonfly if you’re fishing the Lower Sacramento River so there’s no reason to carry a stonefly nymph in your box. Focus down to a selection of 6-8 patterns that cover the spectrum of trout flies you might use for fly fishing your river of choice.
Once you’re on location there are several options for determining which flies to use. Dry flies are easy. If you see bugs hatching and trout rising to them that’s your bug. It can be difficult to figure out a masking hatch at times. That’s when you have several species of insect coming off the same time and trout being selective on one specific insect. Fortunately, it’s not a very common occurrence. Generally, if you pay close attention, you’ll be able to figure out which flies the trout are on and then match the size, shape and color and you’re in business.
Subsurface flies are more difficult. When there’s no sign of activity for dry flies you need to focus your fly fishing on nymphs. This is when you need to determine which flies the trout of feeding on. In my early days I used to seine every river that I fished to see what type of insects were in the drift. This is a technique where you stretch a fine net in the water mid-current to collect the insects as they tumble downstream. Knowing which species and what size bugs are available to fish can narrow down your selection to a couple of flies. At that point I would select a mix of patterns and see which bug the trout were focused on. Sometimes it would be a smorgasbord. The trout may take any of those insects available to them. Other times fish were selective, focusing on one size or species of bug. This is pretty common, especially on tail waters. By seining the river first, you get an understanding of where to start your fly selection and then the fish will focus you down on the bug they want.
The quickest way to determine what trout are eating is by letting them tell you themselves. I have two different friends with PhD’s that also work as fly fishing guides. They often use the scientific method to determine which flies to use when they’re after trout. They use a stomach pump on the first couple of trout they catch to see what the fish have been eating. You can use searching nymphs to start your day and once you hook and land a fish a quick check of their stomach contents will dial you in to the flies you should be using.
For some reason pumping stomachs on trout became controversial for a while. There’ve been several studies that prove, when done properly, pumping a trout’s stomach doesn’t have any effect on fish mortality. (You can see the proper technique for pumping trout stomach here) Without a doubt, pumping stomachs is the most efficient way to figure out which flies to choose for a day of fly fishing. The drawback is that you must catch a fish first to make this happen. While seining a river will get you in the ballpark with which bugs are in the drift but pumping a stomach will tell you exactly what’s on the menu. Some of the best fly tyers of all times used to pump stomachs to see insects in their natural state and then copy them at the vice. It’s a great educational tool and if you haven’t tried it before I suggest you do it.
When you first start fly fishing narrowing down the patterns and species of bugs can be daunting. Your first consideration in selecting flies for a day of fly fishing should be size. I’ve spent a good amount of time underwater watching trout feed. In the clearest rivers they have about a second half to react to what they’re seeing. They have to make a quick go/ no- go decision. If it looks like food they eat it. If it doesn’t, they pass. In my opinion size is the most important criteria in that decision. I’ve seen trout pass on size 6 golden stonefly nymphs to eat size 18 mayfly nymphs consistently because that’s what they were dialed into. Even though the larger stonefly would give them a much bigger bang for their buck, they were selectively feeding on mayflies and so the size difference was the number one selection criteria. When you are selecting flies, get the size right first and go from there.
The second criteria should be shape when you’re selecting your flies. This may seem obvious but if trout are eating mayflies, then you need to throw a mayfly imitation. If they’re on caddis nymphs then you should fish a caddis nymph. Think about the shape of the fly they are eating and try to match it. Some mayflies are thin and elegant while others are thick and heavy looking. A small caddis nymph can look very similar to a large midge nymph. Trout are only seeing silhouettes as they feed. Having the right shape on your fly can make as much difference as the right size.
Color should be the final determining factor. With dry flies color can be a major to get the trout to eat. But subsurface, water does interesting things to color. The deeper you get the darker it is, and the less color is available because of light penetration. A red fly at the surface will be gray at 5 feet. When choosing your flies if you know the exact color of the insect you’re imitating then by all means use that color. If you’re not sure then go with something close and it will likely be good enough.
Finally think about where you’re fishing the flies that you chose. If you’re fishing true nymph, meaning the larval form of the insect, you want them to be near the bottom were a natural stonefly nymph, caddis nymph, or mayfly nymph would be in the drift. True nymphs should be your bottom bug in a two bug nymphing rig. If you’re fishing mergers trout are more likely take them as the insect rises through the water column so your emergers should be the top bug in a two bug nymphing setup. You can find more information on nymphing techniques in my article here Fly Fishing with Nymphs.
With dry flies figuring out what type of water trout are feeding in can lead you to the right flies. As mayfly nymphs emerge, they generally spend some time on the surface to dry their wings. Trout will hang in gathering currents like eddies, foam lines, and seams to take advantage of that behavior. Caddis emergers will push through the meniscus (water surface film) skitter off and be gone. So trout will often stage below riffles and near faster currents where they’re likely to catch an emerging caddis trapped in the surface film. Figuring out where the trout are holding can give you a clue to what they’re eating.
Nothing makes more of a difference in fly fishing than confidence. Seining a river to understand which bugs are in the drift or pumping a trout’s stomach and knowing exactly what they’re eating will give you confidence in the flies you choose. That confidence will make you fish the flies you chose better. Fishing flies better means you’re catching more fish. You can improve your success in fly fishing by using these techniques when choosing flies and increase your catch ratio next time you’re on the river.
