Learning how to read the water
Finding fish is the first step to a successful outing. In moving water, predatory fish hold in the same types of places whether they are trout or smallmouth bass.
Fish in streams and rivers have two primary survival motives: 1) Finding shelter from the current and from predators; and 2) maximizing feeding opportunities.
Generally, there is more food in faster current because, like a conveyor belt, faster current moves more food toward the stationary feeding fish. However, trout, bass, and other predators must expend more energy in fast current, and if there's not much drifting or swimming food, the effort may not be worthwhile.
In addition to shelter from the current (and access to food), bass and trout require protection from predators such as otters, osprey and other birds of prey, wading birds such as herons, and humans. Large bass and trout are often conditioned to hold in places that are difficult to reach—under an undercut bank, under a weed mat, under an overhanging tree branch, at the bottom of a deep hole, or behind a rock in fast whitewater. All these places offer both feeding opportunities and shelter from predators.
Because of this constant balancing act, the most logical and obvious places to start looking for trout in moving water are areas where there is a current change—places where trout can sit in slower water, yet have close access to faster water, where they can dart out, grab a food item, and return to their holding spot.
Be aware that these holding spots are not equally productive at all times of the day and in all seasons. A shallow flat that is barren all day long may be the hunting ground for large browns at night when darkness provides the "protection from predators" condition.
Cold water lowers fish metabolism, causing them to feed less and seek water where they expend less energy, therefore favored wintering holes are slow and deep.
In the spring when water temperatures rise, fish feed heavily and move into areas with better access to food. When summer water temperatures rise into the 60s and higher, the oxygen content of the water becomes a factor, and trout move into the riffles and fast water where there is plenty of food and the water is well oxygenated.
Here is a short list of the best spots to find trout and bass:
Undercut banks. A stream or river erodes softer soil layers while the hard-packed top layers—often held together by grass or other vegetation—remain intact. The result is an undercut bank: a trout hotel favored by big trout. They hide from the sun and overhead predators and occasionally dart out into the current to a grab grasshoppers, stonefly nymphs, or prey fish.
It's difficult to get at these fish from directly above since when you walk on the undercut bank, fish can detect your footstep vibrations, and they may spook or develop lockjaw. The best way to present a fly to fish holding under an undercut bank is to wade from the opposite shore or, in a larger river, to drift in a boat and cast as close to the undercut as possible.
Whether you are fishing nymphs or streamers, try not to retrieve the fly away from the undercut too quickly. Dead-drift the fly alongside the undercut, or retrieve it upstream or downstream parallel to the undercut to expose the fly to as much of the undercut for as long as possible. You don't know exactly where the big trout are holding, and sometimes an undercut can run for a hundred feet or more.
Overhanging vegetation. Overhanging tree branches and shrubs provide cover from airborne predators and, as a bonus, they frequently drop terrestrials such as ants, beetles, and inchworms into the water, so consider using these types of fly patterns. If the branches are over the water — but not in the water — it's often possible to cast a dry fly upstream and drift it right under the branches. You can also do this with wet flies such as nymphs and streamers — cast upstream of the tree limbs, and drift the fly under the branches where you suspect the fish may be holding.
If the branches are dragging in the water, getting your flies to the fish is much more difficult. Dry flies usually won't work unless you approach from downstream and cast upstream as closely behind the branches as possible. Sometimes you can still drift wet flies under the dragging limbs, especially if they are only partially submerged and you cast well upstream allowing plenty of time for the flies to sink.
Backeddy. The current in a backeddy is circular. Near shore, the current often moves in the opposite direction of the main current, and fish facing into the current are facing the "wrong" direction in relation to the rest of the fish in the river. It can be difficult to get a dead-drift in a circular backeddy, but the rewards are great: backeddies can hold enormous numbers of fish, especially in fertile spring creeks and large tailwaters.
Behind a rock. A large midstream boulder is a frequent feeding spot for trout because the rock provides a strong current flowing from both sides, and a sheltered spot to sit and watch for food. To catch trout directly behind the rock, cast your fly upstream of the rock and allow it to drift in the current to one side of the rock or the other just as a natural food item would.
Sometimes trout hold well downstream of the rock. In these cases you can cast behind the rock and drift your flies down the current seam until the seam disappears.
In front of a rock. When flowing water hits the front of a rock it pauses for an instant before the water pushing from behind forces it to flow around the rock. This dead zone—often described by angling writers as a "pillow" or "cushion" of water—is an easy spot for fish to sit and wait for food. It is less turbulent, so it's both easier for the trout to see food drifting toward it, and easier for you to spot the fish if the water is clear and shallow enough.
The spot in front of a rock is not a great "holding" spot like a deep pool or even behind a rock. This position is generally only used by fish that are actively feeding. Approach carefully from below and slightly to the side so the fish can't see you. Cast upstream of the rock and allow the fly to dead-drift directly toward the fish. To avoid snagging the rock and losing your opportunity, begin with dry flies and then switch to lightly weighted emergers and nymphs before trying more heavily weighted nymphs or streamers.
Current seams. Wherever a tributary or sidechannel enters a main river; where two currents meet below a rock, gravel bar, or island; or where the current tumbles around an obstruction along the river bank, there is a current seam where two opposing currents collide or where fast current meets slower current.
Trout and bass sit along these seams, using the break in the current to avoid expending energy, yet using the nearby current to bring them food. To catch these fish, your flies should drift directly down the seam like a natural food item.
Head of a pool. A pool is a wider area of a stream or river where the water is also generally deeper and slower. By definition, the area above the pool is constricted some way—either by a narrow stream channel or a shallow (yet wide) riffle. Where this constriction loosens is the head of the pool and it's a major break in both the current speed and depth.
Fish gather at the head of the pool to feed on the food pouring in from the riffle or faster water upstream. In small mountain streams, the head of a pool is often a plunge pool, where water falls over boulders into deeper water below. Trout pick out these areas as both prime feeding and holding areas.
Tail of a pool. The gut of a pool—the deep, dark area in the middle—is a fine place for fish to hide and rest. When they decide to feed, they move to the head of the pool (see above) or drop to the tail of the pool where the water speeds up and is shallower.
When there is a hatch, the shallow tail of the pool can provide excellent fishing because the trout remain on the bottom and still have easy access to the hatching insects drifting overhead. However, the tail of a pool can be a tricky place to get a drag-free drift because you often approach from below, stand in a fast riffle, and cast upstream into much slower water at the tail of the pool. The fast water in the riffle pulls on the line, and can cause dramatic drag if you don't get enough slack into the line.
Tributary. Small streams entering the main river can bring cooler water and additional food sources. They can also produce a current seam fish use to feed. Pay particular attention to these places in the summer when the main river warms and fish gather near the cool inflows. Avoid these places in the spring or after heavy rain when they flood with muddy water.
Bank obstructions. When you drift down a big river in a drift boat, you often "pound the banks" with streamers, nymphs, or big dry flies. While many new fly fishers tend to wade too deeply and focus on the middle of the river, expert anglers know that on big rivers especially, trout avoid the heavy current in the center of the river and use obstructions along the bank to give them both relief from the current and excellent feeding opportunities. Fallen clumps of grass and soil, downed logs, streamside rocks and boulders, irregularities in the bank, fences in the river, bridge abutments, and other debris along the bank all create breaks in the current, and as a result, current seams where fish hold.
Depth changes. Knowing the contours of a river bottom can help you catch more fish. When the water is low and clear, pay attention to the potholes, depressions, and gravel bars that form the terrain of the river bottom.
When the water is higher or off-color, you can use this information to catch fish lying in the deeper spots, feeding on food items passing overhead. Remember that the water on top of the river travels much faster than the water on the bottom, and the water in depressions along the bottom can be nearly motionless, while faster water rushes past overhead.
Riffles. Fish in the riffles are hungry. They aren't there to rest or avoid predators, they are there to feed, and because food drifts past quickly, they have little time to inspect and consider your fly when it drifts past them. Relative to fish in flat, slow water, trout and bass in the riffles are easy to catch. In the riffles, use large, heavily hackled and/or foam dry flies that are extremely buoyant and easy for the trout to pick out and attack.
The bumpy water on the surface of the riffle is caused by numerous rocks and gravel undulations along the bottom. While riffle water might seem fast, obstructions create a slow zone on the bottom. If you are using nymphs, make sure you use enough weight—usually split-shot—to sink the flies quickly and drift them slowly along the river bottom. Your flies should travel slower than the surface currents, therefore your indicator—if you are using one—should actually appear to be dragging to indicate that your nymphs are moving slowly.
When streamer fishing, the turbulence of the water adds all the movement you need. Because of the erratic current in a riffle, trout sometimes have trouble tracking and eating the fly, and may not bother to chase a food item that appears to be swimming too quickly or strongly. Move the fly slowly (from your vantage point) and keep a tight line so that you don't miss the strike.