An important part of successful fly fishing is knowing where fish are living in the river. They hold in different spots for different reasons and understanding why can be challenging. It is also important when rowing or wading in moving water to be able to “read” the waters movement and topography for safety reasons. Like most skills, reading water can be learned.
The study of moving water is called hydraulics and it involves things like gravity, elevation change, surface tension and friction. We don’t need to dive too deep into that end to be successful at fly fishing but a basic understanding can be helpful. Watching a river for a few minutes will reveal a lot. The steepest elevation changes and center of the channel have the fastest velocity. Water along the banks and bottom is moving slower due to friction. Surface tension slows the bubbles on top of the water. Anything on the river bottom can cause seams and currents that move along the main current and create holding spots for fish.
If a rivers depth and width change, this also changes the effect on the hydraulics. Simple terms we commonly hear to describe these different sections of a river are Riffle, Run and Pool. These terms are describing parts of a river with specific depth, width and bottom characteristics. It can be beneficial to know the definition of each in order to recognize them on the water.
Riffle – Fast, Shallow flow over boulders and cobbles which break the water’s surface
Run – Smooth, Unbroken flow connecting riffles and pools
Pool – Areas of slow flowing, deep water.
In order to understand things a little better let’s take a look at each definition and some of the characteristics that can be found in each section. Imagine you are sitting on the bank of your favorite river and picture a familiar section with fast water that is fairly shallow. It is likely at a point where the river narrows and the elevation changes. The river bottom is made of round stones and possibly large rocks (a rapid?). The surface of the water appears broken or boiling and air bubbles are being created as water flows over and between rocks. This is a Riffle!
Picturing the same river let’s move down stream to a section with a little more depth. The elevation change is a little flatter and the river might have widened a bit. The edges of the banks are more consistent and the bottom is still round stones but they are smaller and there are fewer big rocks. The surface of the water has slowed a bit and is moving at a consistent speed river wide. There are still bubbles on the surface but they are moving in lines and following the seams in the current. This is a Run!
Moving downstream a bit more in our mind lets picture a slower, deeper still section of the river. The elevation change is minimal and there might even be a bend in the river just upstream. The water is too deep to see the bottom but there often is a rocky shelf where things drop off. The surface of the water is smooth. There might be a point along the bank on the outside of the bend where the current stops flowing down stream and is flowing back up stream (an Eddy). This is a Pool!
Now that we have these sections of a river fresh in our minds we can learn why and when a fish would be living in each.
Trout living in a river generally have three needs. They require food, oxygen and shelter to live comfortably. Reading the water will help us mentally check those boxes. Let’s look at what a Riffle provides. The constantly moving water over a rocky bottom where the bugs (nymphs) live is a steady supply of food. Check that box off. All of those bubbles being created by the steep gradient and fast water means lots of oxygen, Check that box. Those large rocks that we pictured provide the right kind of shelter for a trout to get out of the current and hide, Check that box too. All three needs are being met which means that it is very likely to find feeding trout in a Riffle.
Let’s take a closer look at a Run. Water is a little deeper and the river bank is consistent which can provide cover (undercut bank?). The bottom is still rocky so fish also have shelter, let’s check that box. The flow is more consistent but there are varying currents river wide with bubbles lined up, that’s oxygenated water. Check that box. A run typically follows a food rich Riffle and is characteristically a rocky bottom so it will have bug life. Food, check! Water temperature will still be cool and the deeper parts will be even cooler in Summer. Likely place to find feeding trout? You bet! A Run can often be the best place to find the most numbers of feeding fish.
Moving down to the Pool, let’s see what we find. Deep, cool water with a possible shelf for cover. Check. Fewer bubbles but they are still there so oxygen is present. Oxygen, check. Water is still moving so food is present but it is moving slower. Check. Feeding trout in a pool will often be found on the shelf or the “drop”. It is a steady source of food and they will hold in the deeper water for shelter. Another hot spot for feeding fish in a pool is the “seam” or “eddy line”. This is the point where the main current and current created by the eddy meet. It creates a conveyer belt of food in an area with easy access and protection or the fish.
One more important factor to consider in a trout’s living and feeding habits is water temperature. It is the final factor that will possibly determine where the most feeding fish are living. More feeding fish means a higher chance of catching one. Too cold and trout wont feed. Too hot and they will be stressed. Water in a riffle is often cool and highly oxygenated, therefore a Riffle is sometimes referred to as “Summer Water”. There are usually plenty of food and space for fish to spread out or line up in a Run, so it will be the most consistent place to find fish year round. Often in rivers that freeze during the Winter a Pool will be the last refuge for open water and food. For this reason a Pool is sometimes referred to as “Winter Water”.
Finally, let’s touch on reading water for safety. Weather rowing or wading it is important to remember the power of moving water before getting in. At high water even the bank will be unstable and potentially dangerous. One foot of water (calf deep) moving at a medium pace is powerful enough to move a vehicle. Hazards like “strainers” are things in the river that water will pass through but a person won’t. That’s a very dangerous situation for anyone in the water. Learning to recognize the main channel and reading the water for hazards, upcoming rapids and passible lines is crucial for safely rowing. Getting a guide or taking a class on rowing is the best possible choice before setting out. Contact Cutthroat Anglers staff for more information on either option. Explore, breathe, practice reading the water and fishing possibly turns to catching.
Share this post: