Reading Water For Trout

Being able to “Read” water will tell you where the biggest
fish in the stream is located. waterBeing able to “read” water is essential to becoming a competent fly fisherman. If you don’t understand where trout position them selves in a stream,  you’ll only catch them by happenstance.By knowing how to read water, you can know exactly where to start fishing and what to expect. The principles of reading water are the same no matter the size of the water.  The characteristics are the same for a stream you can step across up to a river the size of the Mississippi.  An eddy in a brook has the same characteristics as an eddy in  the Mississippi. Only the scale is different.

Here’s what you need to know. 

The “body” parts of  a stream are:  riffles, runs, pools, flats, and tails in that order. The gradient of a stream bed determines the speed of the water.  The speed of the water varies from top to bottom depending on how much friction is created by the bottom.  The fastest water will be at the top and the slowest at bottom.  Obstacles and obstructions in the water alter the flow and speed of the water around them—from top to bottom. Trout live on the bottom. Whitlock “Guide To Aquatic Trout Foods” bookDave Whitlock says in his excellent book Dave Whitlock’s GUIDE TO AQUATIC TROUT FOODS  “ knowing water types and the special properties of each will provide the serious fly fisher with immediate clues for selection of the best natural-food imitation” or in other words, what fly to tie on the end of your line. example
Riffles are characterized by their irregular, rough, broken, fast-moving surface. Rocks and boulders protrude above the surface and cause the water to foam and “dance”. Most sizes of trout can live in a riffle, since they easily hold in the
calm spaces next to the bottom rubble or behind and in front of boulders or rocks, grass beds and logs. Riffles are the food factories for trout.  In a riffle under, on, and among the rocks is where the trout food is. Under, you will find nymphs, scuds, and larva.  On, you will find cased caddis and midge larva.  Among, will be minnows.   Real shallow riffles generally do not hold a lot of fish. Riffles with depth however, can be real hot spots The run.

Immediately downstream of the riffle is the “run”. river run Here the water deepens and slows as it moves to the pool section. The stream will widen or narrow but always become deeper than the riffle, and the water flow slows.  
In the head of the run you will find the “tongue” characterized by a wide fast flowing upper part narrowing to the tip with eddy lines and back swirls on both sides.  Think of the tongue as a feeding funnel for the trout.  Trout will hold along the edges adjacent to the eddy line and in front of boulders, logs, or any obstacle that slows or breaks the current, which allows them to conserve their energy.  The edges of the tongue are very productive areas.  Where the tongue peters out is usually the deepest part of the run that becomes the pool. The largest trout lie in this section on the bottom waiting.  When a hatch begins the dominant trout will move to the head of the run and take the prime feeding position. Runs can be  long stretches of smooth flowing water that are generally consistent in depth. “Pocket” water is a run that has lots of submerged boulders.  Runs hold lots of fish.  The total lenght of a run if (it’s pocket water), can be fantastic fishing.

The pool section is the “pool” fishingdeepest and widest part of the stream characterized by eddies, and back-eddies, where the water flow almost comes to a stand still.  The shallow side of the pool will slope to the high bank of the deep side where the current flow is faster than the shallow side.  The bottom of the shallow side will have silt, gravel or debris accumulated.  Many pool sections will have back-eddies where trout will be facing downstream instead of upstream.  In the center of a back-eddy the water slows almost to a stop.  Trout will meander there looking for food items that may flow into the back-eddy from any direction relative to their position.  Along the high bank in the deeper water of the pool is where most of the trout will hold. Pools tend to be heavily fished, especially by beginner fly fisherman because they are so inviting. They think, “deep water, big fish”. From the pool portion the water flows to the “flat”. 

The flat is that section of the body that forms after the pool primarily because the slope of the bottom slopes upward causing the water to “spill” out into a broad area. This area although rich in food for the trout can be difficult to fish because of the swirling characterizes of the water.  Getting a good sustained drift can be frustrating.  Note: most high gradient streams do not have flats.  Flats are more common to larger or broad rivers like the Henry’ Fork in Idaho; which by the way, can produce fabulous “flats” fishing. mile runFinally from the flat area the “tail” emerges.  Here the water shallows and picks up speed due to the narrowing of the stream.  The water has a slick oily appearance unless relatively large rocks or boulders are present.  Tails are very productive fly fishing spots.  They’re easy to wade and to spot raising fish.  Like the “tongue” that feeds the run so is the tail.  Here the trout can casually pick of emerging insects without having to battle strong currents.   Be careful to scan and observe the tail section because the largest fish in the stream may be resting or feeding there. A large fish  in the tail can easily spot predators (that would be you). There is deep water close by he can flee to– if surprised.   Fishing dry flies in tails can be very difficult because the currents play havoc with a floating fly line.  On the other hand fishing a sinking line can be very productive.  Tails are prime spawning areas for trout.