Understanding Trout and Their Environment(fly fishing)

“In order to do, we must first understand what it is we are doing.” Therefore, understanding the environment that Trout inhabit is essential to learning how to fly fish for them. Consequently, you must first understand that from the day a Trout is born as an egg to day it dies, there are aquatic, terrestrial, and avian predators that are looking to make a meal of it. Thus, if a Trout is to survive, it necessarily becomes very paranoid! As a result, all Trout seem to adopt an attitude of “If it moves, RUN! If it doesn’t move, RUN ANYWAY!” Thus, if a trout sees any movement whatsoever within its cone of vision, its first instinct is to dart into the nearest Sheltering Lie and stay there until he feels like the threat has passed. So, as a fly fisherman, it is absolutely imperative that you learn to become very stealthy in your approach to a prospective trout lie. In fact, when fly fishing for trout, it is helpful to adopt the attitude of a hunter rather than that of the average fisherman. Therefore, you should take advantage of any available cover to hide your approach to a prospective trout lie such as moving along the bank where your are hidden by trees instead of wading up center of the stream, hiding behind boulders, or crouching down so that you are below the trout’s cone of vision.

Understanding Trout and Their Environment

How a Trout Sees His World

Although understanding how a fish thinks is paramount to enabling you to catch fish, it is also important to understand how they see their world. Thus, the following description applies to all fish species in any type of water but, this section will focus specially on Trout. Thus, if you were a Trout lying on the bottom of a stream, if you were to look up, you would see a huge mirror hanging over your head and that mirror would reflect an exact replica of the stream bed and anything located beneath the surface of the water. However, you would also see a round hole in this mirror located directly above your eyes that would provide you with a limited vision of the world above the surface of the water and, the cause of this phenomenon is a law of physics called Snell’s Law that states “any light waves striking the surface of water at an angle that is greater than 45 ° will enter the water and, any light waves striking the surface of water at an angle that is less than 45 ° will be reflected”. But, unless you are holding in perfectly still water, the image of the surface world you see through this window would be distorted by the current and any ripples caused by riffles, runs, or rapids. Thus, if you were holding in white water (as Rainbow Trout often do), then instead of seeing an image of the surface world, you would instead see a white froth of air bubbles and distortions caused by the current.

In addition, the size of the hole through with you see the surface world would depend on the depth at which you were holding because, the diameter of the hole through which you can see is two-and-one-quarter times the depth at which you are holding. Therefore, if you were holding at a depth of two feet, then you would have a round window over your head approximately four and one half feet in diameter through which you could see the surface world. In addition, because the shape of this hole extends at a 45 ° angle from either side of the trout’s eye (with the apex of the angle being located at the tout’s eye), trout have 90 degrees of vertical vision under the water’s surface. However, once the edge of this angle reaches the water’s surface, it descends to a 10 degree angle. Consequently, trout actually have 160 degrees of vertical vision which is shaped like a cone extending upward from their eyes and thus, we call this their “Cone of Vision”. Therefore, a fly fisherman approaching a potential trout lie will only have a 10 degree angle from the surface of the water in which to approach the trout unseen! However, it is important to keep in mind that since this is an angle, it widens accordingly the further the apex is from the water’s surface and narrows accordingly the closer the apex is to the water’s surface. Therefore, the closer to the surface that a trout is holding, the smaller his cone of vision will be and the deeper he is holding, the wider his cone of vision will be. Also, the farther you are away from where a trout is holding, the less likely it is that he will see you and conversely, the closer you get, the more likely it is that he will see you.

Thus, the average fly fisherman of average height wading in water that is approximately waist deep will only be able to approach a potential trout lie to within about fifteen feet without being seen and even less if you walking along the bank even with, or above, the water’s surface. So, if you feel the need to approach the trout’s lie any closer than this, you will need to crouch down closer to the water’s surface or, use any available cover such as rocks or boulders to hide your approach. In addition, it is also important to keep in mind that trout have 330 ° of horizontal vision beneath the surface of the water which leaves a 30 ° blind spot directly behind them. Thus, since trout are anatomically designed to face upstream into the current, it is always best to approach a potential trout lie from downstream so that you approach them within their blind spot. Last, while trout do have rudimentary ears and thus, they can hear some sound beneath the water’s surface, they have a far more sensitive organ called the “Lateral Line” which extends the length of their body from head to tail that consists of a group of highly sensitive nerves that enables them to feel or “see” pressure waves in the water. Thus, when you are wading in the water and approaching a potential trout lie, it is imperative that you do so in as stealthy a manner as possible and as slowly as possible in order to minimize the pressure waves crated by your body moving through the water. Consequently, approaching a wild trout in its natural environment without being seen or felt is a daunting task at best and one that takes years of practice to perfect. Therefore, anyone who is able to approach a wild Trout, then cast their fly precisely enough to land it within the trout’s “cone of vision”, and then cause that fly to drift in a way that looks entirely natural and thus entices the trout to take the fly, has accomplished a phenomenal feat of planning and stealthy execution of which they should be extremely proud regardless of the size of the trout they catch!


The Food vs. Energy Equation

Furthermore, you should also be aware that trout are first born as

an egg and then, as they mature, they grow through different stages based upon their size called Alevin, Fry, Fingerlings, Parr, and Juveniles before becoming sexually mature and thus being classified as Adults. Consequently, once a trout completes the Alevin stage by completely consuming its yoke sack, the only two things on its mind are avoiding predators and finding and consuming enough food to grow larger. Consequently, all trout look for quite spots in the stream called “lies” where they can escape the constant pull of the current and yet have easy access to food without unduly exposing themselves to danger from predators. Therefore, such places as eddies located behind rock or a log adjacent to good current flow make excellent “prime lies”. In addition, it is important to learn to identify prime lies because you will always find the largest trout in the prime lies. But, the reason for this is a concept called the “food vs. energy equation” which states that, in order for a trout to grow larger, it must gain more energy from the food it consumes than it expends in pursuing and capturing that food. Thus, it is helpful to think of the stream as a floating restaurant and the various aquatic and terrestrial insects drifting in the current as the menu and a trout’s “prime lies” and “feeding lies” as their seat in the restaurant. So, when a tasty looking insect comes drifting downstream toward a trout’s prime lie or feeding lie, all a trout has to do is decide whether or not he wants to dart out into the current and capture that insect.

However, it is important to be aware that there are also numerous bits of organic debris drifting in the current along with all those tasty insects and thus, a trout must become very adept at discriminating what is actually edible from what is not edible and they learn to do this by learning to identify the size, shape, and color of the available insect species that inhabit or fall into their particular stream. In addition, they also look for signs of movement such as the gills located along the abdomen of May Fly and Damsel nymphs as an indicator of life because any trout that mistakenly captures non-edible food is wasting energy. Plus, any trout that spends time swimming in the current to capture food is also wasting energy unless there is a tremendous amount of food drifting in the current such as when a May Fly hatch is occurring. Thus, when such hatches do occur, trout will often leave their sheltered prime lies and hold in the center of the water column in the middle or tail of a pool in Feeding Lies in order to more easily capture these nymphs and the emerging Duns. But, this exposed position also makes them far more vulnerable to avian predators and thus, they are often very skittish when they are in feeding lies. However, the overabundance of food drifting in the current often makes the extra risk well worth the danger. Now, in addition to the various species of aquatic and terrestrial insects drifting the current, there are also numerous species of small fish inhabiting the stream along with the adult trout such as Dace, Sculpins, and Chubs, and Crayfish along with trout in the various stages of maturity, and all of them are fair game as far as adult trout are concerned.

Thus, I like to think of these various bait fish in this manner: if someone were to offer you your choice between a free McDonald’s cheeseburger and a free 20 oz. steak dinner, which one would you choose? Personally, I would choose the steak dinner and most adult trout seem to feel the same way. So, although it obviously requires more energy to run down and capture a bait fish than it does a May Fly Dun, that baitfish provides FAR more energy than consuming a couple of nymphs mature adults. Therefore, trout will almost always consume the largest meal available as long as it provides them with more energy than they expend capturing that piece of food. Consequently, larger flies tend to catch larger trout. But, it is also important to understand that when there is an overabundance of nymphs and duns drifting in the current such during a hatch, then trout will often become very selective in what they choose to eat for the duration of that hatch. Thus, they will often ignore any food item that is not the same size, shape, and color of the hatching insects because they have already determined through sampling that a particular insect is an edible source of food and thus it satisfies the food vs. energy equation.

The Three Types of Trout Lies

As I mentioned in “The Food vs. Energy Equation” section, trout live in a constantly moving environment and thus, in order to conserve energy, they look for places in the stream that provide them with shelter from the current and these places area called “trout lies”. However, as a fly fisherman, it is important that you understand that there are three different types of trout lies and each one serves a different purpose to the trout. For instance, trout need places that they can run to for shelter whenever they feel threatened either from above or from below and we call these places “Sheltering Lies”. Therefore, any trout that exists in given stream has undoubtedly thoroughly explored that section of the stream and thus, they know exactly where any nooks, crannies, ledges, and undercuts are that they can squeeze into deep enough to escape any predator that may be pursuing them. In addition, their instinct tells them that if they see any movement at all through that magical hole in the mirror above them that we call the “cone of vision” that might represent a danger to them, then their unconscious reaction is to dart for the nearest Sheltering Lie as fast as possible and stay there until they are certain the danger has passed. Therefore, a Sheltering Lie is defined as a place that provides a trout with shelter from predators but does not offer access to food.

Consequently, good examples of Sheltering Lies are under or between large rocks, deep into the dark caves created by overhanging ledges, or beneath undercut stream banks. On the opposite end of the scale, there are places in the stream where trout will gather during times when one species or another of aquatic insects are hatching even though it exposes them to predators and these places are called “Feeding Lies”. However, these Feeding Lies are often chosen specifically because they require the trout to either expend very little energy to maintain their position in the current or, because that particular position concentrates the stream of hatching insects so that the tout can eat more of them while expending less energy. Consequently, these Feeding Lies most often occur in calm pools and glides where the water is crystal clear and the trout can suspended above the stream bed or in the shallow tail of a pool. Therefore, a Feeding Lie is a place where trout congregate only because it provides them easy access to an overabundance of drifting aquatic insects but, does not provide them with shelter from predators. Last, there is a third category of Trout Lies that is the ultimate place in the stream for a trout to hold because it offers the trout both shelter from predators and easy access to food and these types of lies are called “Prime Lies”. Consequently, no matter what stream, creek, or river you fish on, you will always find the largest fish in the Prime Lies simply because the Prime Lies are the best real estate available in that section of water and the largest, most aggressive, trout will always displace the smaller trout in the Prime Lie for that reason.

After all, look at Japanese Sumo wrestlers; the ones who eat the most get the biggest, and the biggest Sumo wrestler is the one that usually manages to toss the opposing wrestler out of the ring. Therefore, the way to identify a Prime Lie is to first look for places in the stream that would offer a trout shelter such an eddy behind a large rock, an eddy behind a log protruding into the stream or laying on the streambed either adjacent to or in the main current, or a ledge with a deep cave that faces upstream so that the trout can see any food items drifting toward it without exposing itself to danger. Also, the eddies on the edges of riffles and runs are also Prime Lies because the turbulent surface of the water makes it nearly impossible for predators to see the trout even in shallow water. In addition, the small pockets found in “Pocket Water” are excellent Prime Lies because the turbulent water around them sweeps a lot of food into the pockets. Last, water deeper than four feet (even if it is crystal clear) usually causes a trout feel reasonably safe and thus, they will often cruise in deeper water while rooting for nymphs or plucking Periwinkles. So, now that you know about the three types of Trout Lies, the next time you approach your favorite trout stream, try approaching slowly while using the intervening foliage to conceal your presence and take some time to see if you notice trout congregating in the tails of the pools or cruising in the pools or glides and, if not, then proceed to approach and cast your fly only to the Prime Lies because everything else will either be barren water or hold only small trout.

The Different Types of Trout Flies

The types of flies that fly fishermen use can be divided into several different categories and each category has its appropriate time and place. However, as a general rule of thumb, dry flies are the most exciting pattern to fish, nymphs tend to catch the most fish, and streamers tend to catch the largest fish. Now, the reason that dry flies are so exciting to fish is that when you are fishing on the surface, you can often see the fish rising to the surface to take the fly but, you have to set the hook very quickly or the fish will reject the fly. Nymphs, on the other hand, are often the most productive category of fly to fish with because trout often obtain the majority of their food from the sub-surface drift because it requires less energy and presents less danger than rising to the surface. Last, once a trout reaches maturity, it often becomes very difficult for them to obtain enough food from the drift and thus, they often turn to larger prey to satisfy their energy requirements. Therefore, streamers tend to attract the largest fish because they imitate forage fish such as Sculpins and Dace and crustaceans such as Crayfish.


Nymph patterns are fished sub-surface on or near the bottom and are generally designed to represent May fly or Stone fly nymphs but, there are also some good, free-living and cased, Caddis fly larva imitations as well as some good Hellgrammite (Dobson Fly) imitations. Also, May Fly nymph patterns are designed to imitate immature May Flies that have accidently become dislodged from the rocks and gravel on the stream bed or nymphs that are rising to the surface to hatch. Whereas, Stone Fly nymph patterns are designed to imitate immature Stone Flies that have become dislodged from the rocks and gravel on the streambed and are tumbling in the current. Last, Hellgrammite patterns (aka “Grampers”), are designed to imitate the larval stage of the Dobson fly and are very aggressive predators of other aquatic insects. Thus, they are very mobile in the current and have large and powerful mandibles that can deliver a painful bite to both their pray and humans but, despite their ferocity, they are a favorite food of both Trout and Smallmouth Bass.


Larvae patterns are also fished sub-surface on or near the bottom and are generally designed to represent either free living or cased Caddis Fly larva that have accidently become dislodged from the rocks and gravel on the stream bed

Dry Flies

Dry flies are fished on the surface of the water and are generally designed to imitate either adult, adolescent, May flies or Caddis flies. Furthermore, Mayfly imitations are divided into two sub-categories called: Duns and Spinners whereas, a Dun imitates a mature adolescent May Fly that has just hatched and crawled out onto the surface of the water to let its wings dry before flying to the streamside foliage to complete the next stage of its life and a Spinner imitates a mature, adult, female, Mayfly that has returned to the water to lay her eggs and then died while over the water after having completed her lifecycle. Looking deeper into the May fly’s life cycle, we see that they are born as eggs laid on the streambed which then hatch into nymphs that inhabit the steam bead for one to four years (depending on the species) before hatching into duns. Then, when the nymph is ready to hatch, it inflates its exoskeleton with air and rises to the surface where it suspends itself in the surface film. Once there, it splits open is carapace and crawls out onto the surface of the water to let its wings unfurl and dry at which point it is called a “Dun”. After its wings are dry, the insect flies away to the streamside foliage where it stays for about two weeks while undergoing a second metamorphoses.

After fully maturing, the Dun molts and emerges from its exoskeleton again as a sexually mature adult which is called a “Spinner”. Caddis fly imitations, on the other hand, are many fly angler’s favorite dry fly pattern and they are designed to imitate an adult Caddis fly that is returning to the water to lay its eggs. Looking a little deeper into the life cycle of the Caddis fly we see that Caddis flies are born as eggs laid on the streambed that then hatch into larvae of two different types depending on species. After hatching, some larva build a cocoon to which they attach small pebbles or sticks and leaves (aka “pebble bait” and “stick bait” respectively) while other species live as free roaming, predatory, larva. However, when both types of larva are ready to hatch, those that don’t already have cocoons build them and then both types seal themselves in like a caterpillar and then undergo a metamorphoses into a sexually mature adult. Once the metamorphosis is complete, the adult exits the cocoon, quickly rises to the surface, and then exits the water immediately. Consequently, all dry fly patterns are intended to be fished on the surface and allowed to float along with the current but, it is absolutely imperative that they be drifted drag free in order to appear as natural insects to the trout. Otherwise, they will be ignored.

Wet Flies

Wet fly patterns are designed to be fished sub-surface in the top or middle of the water column and are designed to imitate adult May Fly duns that have either drowned while floating on the surface of the stream waiting for their wings to dry or died while flying over the water after laying their eggs. In addition, they differ from dry flies in that they are made from soft hackle material instead of stiff hackle material and their wings are swept to the rear instead of standing upright. However, they too must be drifted drag free in order to appear as natural insects to the trout.


Emerger patterns are fished in the surface film and are designed to represent a Mayfly nymph that has risen to the surface and is suspended in the surface film while it splits its carapace to emerge as a Dun.


Terrestrials are a sub-category of dry flies and thus they are fished on the surface like a dry fly. Also, Terrestrial fly patterns are

designed to imitate insects that live on the ground or in the trees along the side of a stream which have accidentally fallen into the water or been blown into the water by the wind. Thus, terrestrial patterns such as beetles, ants, and inchworms, ect. make excellent search patterns for the late spring through late fall months.


Streamer patterns are fished sub-surface near the middle or bottom of the water column and are designed to imitate small baitfish that live in the stream such as Trout, Dace, Darters, and Sculpins.


Imitator patterns are what most people envision when they think of trout flies. However, they can be either dries, wets, or streamers that are tied to closely resemble actual species of aquatic insects, crustaceans, and forage fish. Thus, use imitators when fish are rising to insect hatches, when fish are finicky and refuse attractor patterns, and in calm, clear, water where fish have plenty of time to look at your fly before choosing to inhale it.


Attractor patterns are brightly colored dry fly, wet fly, and streamer patterns that don’t resemble any actual insects or forage fish but still draw strikes nonetheless. However, biologists, fly tiers, and experienced fly fishermen all generally agree that there are some combinations of colors that automatically trigger the strike instinct in fish. For instance, trout are often triggered by the colors red, yellow, and green and a combination of red and white, yellow and white, and green and white while Smallmouth Bass are often triggered by the colors olive green and chartreuse. Thus, attractor patterns are often useful for locating fish when there is no hatch coming off and/ or the fish are not actively feeding. Also, attractor streamer patterns are often useful in turbid water because they are easier for the trout to see.


Click Here to Leave a Comment Below