“What fly should I use?” This might be one of the most loaded questions in all of fly fishing. There are so many points of confusion and borderline superstitions that a lot of anglers get hung up on. If you were to ask three people about which fly pattern you should use tomorrow on a given river, you are likely to get 3 different answers. The truth is that most of the time, close enough is good enough when selecting a fly pattern. If you have some basic knowledge about the species you are targeting and the fishery itself, you probably have many “correct” options when choosing a fly. Also, it is worth noting that how you present a fly is almost always far more important than the pattern itself. There is no substitute for experience on the water. The more time you spend fishing, the more intuitive fly selection becomes.  Below are some considerations that you may find beneficial when selecting a fly.

Taking the time to get a good understanding of the behavior of the fish you are targeting will be a huge advantage in selecting a fly. A lot of this information is easily accessible, and with a little effort, you can use this knowledge to give you an edge over the fish. For instance, having a basic understanding of how water temperature impacts trout behavior can give us some clues in selecting a fly. In winter conditions when a trout’s metabolism slows, it might be wise to select a nymph that rides close to the bottom and is easy for the trout to eat without expending a lot of energy. A dry fly requires a fish to expend quite a bit of energy to leave its holding lie and come to the surface, and might be a much lower percentage option in those same winter conditions. Another example would be fishing for smallmouth bass in the springtime. Spring smallmouth are notoriously aggressive and territorial during the spring because they are entering their “pre-spawn” phase. In this situation, using larger streamers might outproduce smaller ones, thus taking advantage of this behavior. 

In the same way that understanding your target species gives us some clues to selecting fly patterns, knowing your fishery (the water you are fishing) is equally important. This information can tell us to what degree different food forms are available to the fish. For example, Pennsylvania spring creeks are known to have an abundance of freshwater crustaceans like scuds and cress bugs, while freestone rivers might lack that type of aquatic life altogether. Tailwaters are known to produce much smaller mayflies on average than other rivers. Particular streams might have specific hatches at certain times of year that the fish might key in on during those times. By knowing these types of details, it can really pare down the type of flies that are likely going to be effective in a given fishery.

River and weather conditions are always a primary consideration when choosing a fly. Is the water low and clear, or high and dirty? Is there light rain with heavy cloud cover, or is it a bluebird sunny day? Are you fishing during the summer or winter months? These are all important factors and can be a great starting point for many of your on water decisions. Aquatic insects often hatch better on cloudy days. Terrestrial insects are often blown into the water on windy days. Larger flies might be more noticeable to the fish when the water is dirty, and smaller flies might not spook the fish as much when the water is clear. The more time you spend on the water, the more you put together some of these connections and the more intuitive this becomes.

As you can probably already tell, there is no substitute for experience and local knowledge. Taking advantage of the people and resources that are there to help you can go quite a long way, especially if you are new to the game. A great starting point is to touch base with a local fly shop. The guides and shop employees have already put in the legwork in understanding their local rivers, and will be happy to point you in the right direction. For more popular rivers, there are hatch charts, articles and even books that can give you a lot of useful intel. Booking a guide trip might be a great option if you are new to an area, or simply want the most direct line to finding some success. Fishing with other anglers who are more experienced than you would also be wise, as sharing knowledge among friends is one of the most effective and most rewarding ways to learn a river. There are also many online resources that give you valuable information about specific rivers. Something as simple as looking at a USGS streamflow gauge to see water levels before you head to the river can give you a leg up before you even lay eyes on the water that day. All of this information that is available to you can give you a great starting point when making some of your decisions on the water, and can take a lot of the guesswork out of the equation.