How to Read a Trout Stream(fly fishing)

Have you ever been out on a trout stream and noticed that some sections of the stream are narrow and swift while other sections are wide and slow? Well, as fly fishermen, we have names for these different types of water and they are Riffles, Runs, Pools, and Glides and, under normal circumstances, the laws of stream hydraulics dictates that these different sections occur in the order mentioned above. Thus, it is important for the fly fisherman to be able to identify each type of water and to understand where the trout are holding in each type of water as well as how to properly present a fly to the trout holding there.

How to Read a Trout Stream

In addition, it is equally important that the fly angler be able to identify barren water versus productive water so that they do not waste their time drifting their flies over or through water where trout are not holding (although the particular locations where trout position themselves are called “trout lies”, trout are said to “hold” there instead of “lie” there). So, what constitutes barren water and what constitutes productive water? Well, first of all, barren water is any water that is to shallow to offer protection from avian predators or which has a bright, sandy, bottom that negates the Trout’s camouflage and thus, outlines him to predators. Productive water on the other hand is water that is 12” deep or more, has a dark bottom, and is either directly in, or adjacent to, the main current. Furthermore, different sections of the stream have distinctly different characteristics and thus, fly fishermen have chosen to give them descriptive names such a Riffles, Runs, Pools, and Glides. But, what is a Riffle, where do the trout hold in a Riffle, and where do you drift your fly in a Riffle in order to place it in front of the Trout? Well, a Riffle is a section of the stream where the current is fairly swift but, the water level is fairly shallow and it flows over a bed of small, round, rocks or pebbles. Thus, the entire surface of a Riffle consists of small wavelets and mild white water. Consequently, Riffles are the aerators of the trout stream and, because they hold the most dissolved oxygen of any section in the stream and, because they offer easy access to food, the entire riffle becomes a Prime lie if it is deep enough. Therefore, to fish a riffle, station yourself either downstream of or adjacent to it, while facing the riffle and then mentally divide the riffle into lanes about a foot wide.

Then, cast your fly to the top of the first “lane” closest to you and let it drift for the entire length of the riffle (or as far as you can) and then, pick it up and recast it to the next lane over and let it drift. Then, you simply repeat this process until you have covered the entire riffle from side to side (called “fan casting”). Last, please note that it may sometimes be necessary to wade into the riffle in order to reach your next lane over which is fine as long as you do it SLOWLY. But, “what about the food vs. energy equation” you might ask? Well, Trout are anatomically designed in such a way that when holding in swift current against a flat bottom, all they have to do is place their lower jaw against the stream bed and the current with push them down and hold them there just like the wing on the rear end of a race car. Then, in order to obtain food, all they have to do is tilt their Pectoral fins just a bit and the current will cause them to rise or descend though the water column. Next, what is a Run, where do the trout hold in a Run, and how do you fish a run? Well, a run is a section of the stream where the current becomes very narrow, very swift, and is usually quite deep (although not always). Thus, because the current is much swifter in a Run than it is in a Riffle, the Prime Lies in a Run are adjacent to the current rather than in it. Therefore, look for large rocks either above or below the surface of the water as well as undercut ledges that will create eddies that provide the trout with shelter from the current but easy access to any aquatic insects drifting in the current. Then, drift your fly in the current as close to those Prime Lies as possible so that the trout has the least amount of distance to cover in order to seize your fly.

In addition, Runs often extend into a Pool below them and thus, you will see a tongue of very swift water that extends into a body of much calmer water. Therefore, the edges of this current tongue are also Prime Lies and thus, you should cast your fly to the top of the current tongue right along the edge of seam between the swift water and the calm water and let it drift the entire length of current tongue. Now, how do we define a Pool, where do the Trout hold in a Pool, and how do we present our fly to them? Well, a pool is defined as a small to large section of the stream that has a flat, calm, surface. Also, be aware that pools can be either very shallow, very deep, or anywhere in between but, they all have a (relatively) calm, smooth, surface. Consequently, this makes it much easier for predators to spot Trout in pools and thus, Trout have evolved super effective camouflage to prevent them from being detected when they are holding in calm water. However, if you take a dark colored object and place it over a light colored background, the dark object is immediately obvious because it is outlined by the light background and the same thing happens to trout when they swim over a bright, sandy, bottom in a Pool.

Therefore, the Prime Lies in a Pool are going to be at the head of the Pool where any aquatic insects drifting with the current will first enter the Pool and along the edges of the current tongue that extends into the pool from the Run or waterfall above it. However, if it is a large pool, there may be other places where the trout are holding such as any area with a dark bottom or a shadow from an overhanging tree (especially if it is strewn with varying sized rocks), behind or beneath logs that either extend into the stream from the bank or are submerged and are laying on the streambed, and along the banks under overhanging trees as long as there is enough current there to deliver a steady flow of aquatic insects. Last, what is a Glide, where do we find the trout in a Glide, and how do we present our fly to them once we find them? Well, a Glide is essentially a Pool that is too long to be considered a proper Pool. For instance, picture in your mind your average, backyard, swimming pool and then, picture that same pool ten or twelve times longer and you will have the idea of the difference between a Pool and a Glide.

Consequently, Glides are the most difficult of all trout waters to fish because the surface is so calm and the water is usually deep enough that the trout have a fairly wide Cone of Vision and thus, they can see any angler coming from a long ways off. In addition, due to the calm current in Glide, the trout tend to cruise rather than hold (although this is not always true). Therefore, in order to fish a Glide, you will need a fast action rod with a light weight, floating, line and a long leader so that you can make long casts that will land gently on the water’s surface and enable you to stay out of the Trout’s Cone of Vision. Furthermore, rather than fish the entire Glide blind, stay on the bank and use the intervening foliage to hide your presence as you slowly sneak upstream looking for cruising trout. Then, when you spot one, move back downstream beyond the trout’s Cone of Vision before casting your fly to it. Consequently, it is extremely important for all novice fly fishermen to become adept at reading the stream and learning to differentiate between barren water and productive water. Also, it is imperative that you learn to determine where the Prime Lies are in each type of water and how to present your fly effectively to any tout holding in those Prime Lies if you are to become a successful fly fisherman.


Click Here to Leave a Comment Below