How To Read A Trout Stream in Riffles, Runs, Pools And Glides

This is chapter 4 of our guide “The Art Of FlyFishing

Anyone who has walked along the banks of a trout stream has undoubtedly noticed that sections of the stream differ greatly from each other in that some are swift and agitated while others are slow and calm. Consequently, fly fishermen have given names to these different sections consisting of Riffles, Runs, Pools, and Glides and, under normal circumstances, the laws of stream hydraulics create these different sections in the order listed.

Therefore, in order to be successful, a fly fisherman must learn to identify each of these different sections as well as understanding where the trout are holding in each section in addition to learning how to properly present a fly to them. Furthermore, it is equally important that fly fishermen also learn to identify barren water so that they do not waste their time drifting their flies through water where the trout are not holding.

Our complete Fly Fishing Guide is divided into different chapters:

  1. The Art Of Fly Fishing
  2. Fly Fishing Equipment: What You Need To Get Started
  3. Where To Go Flyfishing: 4 Ideal Spots
  4. How To Read A Trout Stream – You’re reading this
  5. How to Choose a Freshwater Fly Selection

What Defines Productive Water And Barren Water?

Well, first of all, barren water is any section of a trout stream that is too shallow to provide protection from avian predators or which has a bright, sandy, bottom that negates the trout’s camouflage. On the other hand, productive water is a section of a trout stream that is deep enough or agitated enough to provide cover, has a dark bottom, and provides easy access to food drifting in the current.

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How To Fly Fish in Riffles

So, first let’s talk about “riffles” since they are often very productive sections of a stream to fly fish for trout.

Thus, a riffle is a section of the stream where the current is fairly swift but, the water level is relatively shallow due to the fact that it flows over a bed of small, round, rocks or pebbles and thus, creates an agitated, whitewater, surface.

Consequently, Riffles are the aerators of a 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 is often a Prime Lie.

Riffles: Current is fairly swift, water is shallow

So, in order to fly fish a riffle, first station yourself either downstream of, or adjacent to 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”).

Fan Casting

Reading Runs: Swift Current, Deep waters

Next, we have a section of a trout stream that is called a “Run” which is defined as a section of a stream where the water is confined to a narrow current between the banks of the stream and thus, the current becomes relatively swift and is commonly quite deep.

Thus, because the current in a Run is significantly swifter than it is in a Riffle, a fly fisherman should look for logs, rocks, and small caves that create small pockets of calm water which provide the trout shelter from the current while also providing them easy access to food drifting in the current and then should drift their flies adjacent to these Prime Lies.

Swift current, deep waters

In addition, it should be noted that Runs often extend into a Pool below them and thus, the edges of this current tongue are also Prime Lies. Therefore, in order to fly fish a Run, you should cast your fly to the top of the current tongue and then allow it to drift right along the edge of seam between the swift water and the calm water.

Flyfishing in Pools

Next, we have a section of trout stream that is called a “Pool” which is defined as a section of a stream where the water is contained in a relatively large area between the banks of the stream and thus, its surface is often flat and calm and the current is relatively slow but can be either relatively shallow or quite deep.

However, the calm surface in a pool does make it much easier for avian predators to spot and target their prey and thus, most species of trout have evolved highly effective camouflage to enable them to safely hold in clear, shallow, water. But, regardless of how effective a trout’s camouflage pattern may be against a dark or mottled background, this effect is immediately negated when a trout swims over a light colored, sandy, bottom.

Often flat, can be shallow or deep.

Therefore, the Prime Lies in a Pool are going to be located at the head of the pool where any disturbance of the water’s surface will make the trout less visible to their predators as well as along the edges of any Run that may extend into the pool.

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, behind or beneath logs that are either submerged in the pool or extend into the pool from the bank, and along the banks under overhanging trees.

Reading Trout Streams in Glides

Next, we have a section of trout stream that is called a “Glide” which is very similar to a Pool but, differs in that it is much too long to be considered a Pool. For instance, picture in your mind your average, backyard, swimming pool and then, picture that same pool eight or ten times longer and you will have a good idea of the difference between a Pool and a Glide.

But, like pool, Glides are often the most difficult section of a trout stream to fly fish because the surface of the water is so calm. Also, because the water in both Pools and Glides is often  deep enough that the trout have a relatively wide Cone of Vision, the trout can often see an angler coming from a great distance.

In addition, due to the calm surface and mild current in Glide, trout holding in pools and glides tend to cruise rather than hold although, this is not always the case.

Just like a pool, but much longer

Therefore, in order to successfully fly fish a Glide, you will need a relatively long fly rod with a fast action and a light-weight fly line combined with an extra-long tapered leader so that you can make long casts that will land gently on the water’s surface while enabling you to avoid being seen by the trout.

Last Words On Reading Trout Streams

So, in order to become a successful fly fisherman, it is imperative that you learn how to recognize each of the different types of water found in a trout stream as well as understanding where the trout are holding in each section as dictated by the energy versus food equation.

In addition, it is also imperative that you learn to determine where the prime lies are in each section of a trout stream and how to present your fly effectively to any tout holding in those prime lies. But, once you have mastered this essential skill, you will find that fly fishing for trout in mountain streams to be both far more enjoyable and far more productive.

>> READ CHAPTER 5: Basic Freshwater Fly Selection

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