Reading a stream like a book
by Danie Erasmus
Experienced anglers instinctively analyze a section of water to determine where to fish their flies. When prompted most talk about “reading the water”. This art of reading a stream, or stream craft, is probably as old as fishing itself. The term 'stream craft' was probably first used nearly a 100 years ago by Dr. George Parker Holden when he published Streamcraft: An Angling Manual. Richard W. Talleur used the term 'streamology' in his book Fly-Fishing for trout in 1974 to describe the act of reading a stream. Today, in some parts of the world anglers use 'watercraft' to describe this art.
Anglers spend a lot of time, effort and money on having the right equipment, flies and book knowledge, but nothing beats spending time on the river to gain experience. For many anglers stream craft develops over many years of observation and experimentation to read the water effectively. Sometimes it is a subconscious skill, where without thinking about it, anglers will fish some sections and ignore other. To the untrained eye it looks like the experienced angler has developed a sixth sense in finding fish.
This article aim to have significance at two levels: First, you can use it to improve your stream craft to catch consistently more fish, or secondly, you can focus on becoming a more well-rounded and technically sound fly angler, which does not always mean racking up the numbers.
How do fish read the water?
The skill of reading a stream requires a good understanding of the needs of fish. Trout and whitefish hold in water that is adequately oxygenated, easy access to food, and shelter from predators and the fast current. If a potential holding spot has all three, then it is a prime lie, and if it has two of the three then it is a secondary lie. Obviously the best fishing will be in the prime lies and when breaking down a stream into different sections always try to identify the best lies. Fish hold in a lie based on these needs but they will also move between resting and feeding lies, especially fish relegated to secondary and lesser lies. These fish move from a resting lie into a feeding lane also known as a feeding lie, and back to a resting lie when done feeding. Naturally, fish in a resting lie tend to be more reluctant to take a fly than those in a feeding lie.
The expression 'different courses for different horses' is very much applicable to fish. Different fish species occupy different parts of a stream. Bull trout, mountain whitefish and rainbow trout can share areas occasionally in the stream, but often will occupy different types of water given the predacious relationship between them, especially between bull trout and the other two species. Competition for food, and change of season also impact how these species use habitat.
Bull trout tend to be highly migratory. For the majority of the fishing season fluvial fish hold in deeper runs and pools where they ambush prey. By the middle of July bull trout start migrating upstream to spawn, moving between runs and pools. As these fish move from the larger rivers into the smaller tributaries they often stage at confluences. Here they wait for the water to rise in the spawning streams before making the final ascent.
Most anglers know that one of the most productive areas to fish is at a confluence where two streams meet. The water slows down where the currents meet, forming a long vertical seam. Fish align themselves along this seam, which sometimes extends well past the point where you can distinguish between the two converging currents. Bull trout are notorious for holding towards lower end of a confluence at certain times of the year.
Mountain whitefish tend to be varied in their seasonal movements. Some will hold in the same area, sometimes staying in one specific run or pool, whereas others move long distances between spring holding water and spawning habitat in the fall. However, for the majority of the season mountain whitefish prefer more open water like pools and runs. Mountain whitefish tend to avoid pocket water or any water close to structures like logs, boulders and undercut banks, as these areas are often inhabited by bull trout, a predator. When feeding, mountain whitefish will move up into the head of a pool and even into a riffle if the water velocity is not too fast. In the months of August and September they start to congregate in big schools in deeper pools and runs in advance of their autumn spawning.
An area often ignored by anglers is directly upstream of where currents merge. This section of pocket water has a triangular shape, with the triangle pointing downstream. This triangle can be very productive for mountain whitefish, especially during the months of August and September.
Compared to bull trout and mountain whitefish rainbow trout is less complicated. As long as the water temperature is tolerable, and there is a descent food supply, you are bound to find rainbow trout near a seam.
First published in March/April 2016
It starts with stream gradient
There are a few key components that create habitat for fish, but the primary driving force is stream gradient. A stream's gradient is the measure of how quickly elevation changes as water flows downstream. The steeper the gradient, the faster the water flows, and changes in the stream gradient create features that are suitable habitat for fish. These features can be broken down into fast moving features with steeper gradients such as rapids, riffles and pocket water, and slow moving features with flatter gradients such as pools, runs and back eddys.
Riffles -Riffles are miniature rapids, but unlike rapids that you never fish, riffles are productive water often holding feeding fish. Riffles are formed by water flowing through topography with a steep gradient, resulting in faster moving water. The faster, turbulent water in riffles is mixed with air allowing for the exchange of gases more rapidly than slower moving sections. As a result, riffles have high levels of oxygen, which is a necessity for both fish and aquatic insects such as mayflies, caddisflies and stoneflies. It is therefore no surprise that the highest densities of aquatic insects are in riffles, and where there is food, there will be fish nearby.
Riffles also contribute to the fishing success of other features. Productive runs and pools usually have one or more riffles in close proximity upstream, or even a good riffle spilling directly into them. Fish move from these runs or pools into riffles to feed and when done, they will drop back into a resting lie in the run or pool. Riffles are the pantries of streams and trout and mountain whitefish will often move into them to feed, but keep in mind that riffles are not all the same. Shallow riffles, less than a foot deep, with white water on the surface and that spill into runs and pools usually do not have fish move into them to feed. They are too shallow and probably too fast flowing, and fish, especially rainbow trout, will usually wait at the head of the run or pool waiting for insects to be washed out of the riffle. Riffles with water surfaces that have a more rolling appearance and a depth between one to three-feet are the most likely to have feeding fish in them.
Pools -Pools are characterized by deep slow moving water which has formed when a stream has a distinct change in its direction of flow. This direction change might be sideways as a stream turns sharply to the left or the right, or the direction might be vertical when there is a sudden leveling off of the gradient. Water flowing down a steep gradient will scour the bottom, digging a pool, as the stream suddenly transition to a more level gradient.
Runs -Runs are usually downstream of riffles and pools, and are characterized by deeper water with moderate flow and gentler gradients than riffles. The calm surface water of runs allows for light penetration, which is important for microscopic, invertebrate and plant life. In the interior of British Columbia you can spend more time working your way through a run than on the coast. Interior river systems have higher densities of aquatic insects making them very productive due to sedimentary and volcanic rock formations. Nutrients leach from these rocks to form the basis for life in these streams. This is in contrast with coastal streams where geological formations consist primarily of granite. Streams flowing through granite are nutrient poor and do not support a lot of bug life, and thus the fish are sparsely distributed in coastal streams.
Find the more subtle seams
Although riffles, pools and runs are formed by stream gradient changes, all these features have seams where fish will concentrate. Seams are important, as they essentially function as conveyer belts bringing food to the waiting fish. Most anglers easily recognize a seam as the point or transition zone between faster and slower moving water. A seam can be formed when two currents collide and water is compressed or deflected by obstructions in the stream, changing the direction of flow. These obstructions can be steep banks, rocks, logs or even bridge piers.
Most anglers however tend to focus only on the most obvious seams, which are usually vertical seams. Vertical seams are easy to identify as it is seen as a clear line, or sometimes a foam line, between fast and slow moving water. Seams can also be horizontal, and are harder to identify as they are created by submerged obstructions or sudden depth changes in the stream. To find horizontal seams you often have to form a mental picture of what the bottom looks like by “looking through the water” or by interpreting changes in the appearance of the surface water.
Seams can be subtle and sometimes the only clue to it is a subtle change in the appearance in the water surface. One way to identify changes in the water surface is to crouch down and look for any differences in the reflection of light on the surface of the water. Test any of these subtle changes with a fly and over time you will start to recognize which types of water are productive.
In larger rivers, bends form vertical seams with slow water on the inside and outside of the bend. Most anglers readily identify the potential of fishing on the inside of the bend, but many forget to investigate the outside of a bend, and in all fairness, the outside is sometimes devoid of fish. The slow water on the outside is formed as the water pushes against the outside bank. This creates a buffer zone of slow moving water, albeit often small, from which the faster moving water deflects. The outside seam of large bends sometimes hold rainbow trout earlier in the season. As the river straightens out, a pocket of slow water is also formed on the outside, just below the bend and rainbow trout often sit right against the bank in this pocket.
Sharp corners in streams usually form a deep pool. Deep pools can be difficult to fish effectively, but if the water coming into the corner flows reasonably fast, you are sure to find both vertical and horizontal seams, but anglers often overlook horizontal seams. Horizontal seams are formed by the fast flowing water colliding with the mass of slow water in the pool. The fast water is forced to the surface, and a horizontal seam forms between the fast and slow moving water at the head of the pool. This seam is not as defined as vertical seams, but it is more of a zone of swirling water between the fast and slow water. A lot of food is trapped in this swirling water, creating a feeding zone for fish.
An angler's process of developing stream craft is most definitely a never
endingjourney and not a destination. You never reach a point, or destination,
where you stop learning on the water. Remember that no two days out fishing
are alike, and neither are two streams or two fish. Use this article as a
guide foundation, and apply its guidelines on the streams you fish.