[Editor’s note: This is an excerpt from Tom Rosenbauer’s book, The Orvis Guide to Hatch Strategies, from Universe Publishing. This is the definitive book on understanding stream entomology and how to apply it in successful trout fishing.]
I would predict that less than half of any river holds trout that are more than six inches long. Water in which trout will respond to insect hatches comprises perhaps a quarter of all fish-holding water. So somewhere around 10 percent of a river has the potential for fishing to hatches. If you suspect a hatch, you must read the water in a different manner than you would for fishing streamers or nymphs. In nymph fishing, you’re dragging your flies close to the bottom, looking for fish lying in place waiting for something edible to drift by. Typically, they are not feeding actively and are in deeper water for protection, close to the bottom where current speed is slower. When fishing streamers, you’re often looking for fish that lie in ambush points waiting for minnows or crayfish to swim too close. Or you’re fishing slower water where trout actively hunt for these larger prey items.
Trout responding to hatches will position themselves in active lines of drift, where they get the most insects drifting by per minute. They need to be able to see their prey in advance so they can plan their attack. They need to be in predictable currents so they can hold their position and predict the trajectory of insects as they drift downstream. Rather than thinking of rivers as moving water composed of heads of pools, middles of pools, tails of pools, and riffles, begin to think of rivers with more granularity when fishing to hatches. Look for precise combinations of riverbed and current that meet the following criteria and you’ll have more success.
Where the Insects Are Globally
Not all insects live, hatch, and reproduce in the same kind of water. Most of the very large mayflies like Brown Drakes, Eastern Green Drakes, and Hexes live in silt as nymphs. The adults will more often be found in long, slow stretches of rivers with a sand or silt bottom as opposed to the riffles we commonly associate with aquatic insects. Caddis flies are more common in riffles with lots of rocks and larger gravel. Stone flies and mayflies that hatch from flat, wide nymphs are far more abundant in fast water with large rocks.
Insects are even more particular when they return to the river to reproduce. Most mayflies prefer large expanses of riffles with a wide-open canopy so the adults have room to do their mating dance and can easily find each other. But I’ve seen dense clouds of Trico spinners pick up and move 200 yards before they decided to fall to the river. Caddis flies will lay eggs in everything from very fast to slow water. If you see a bunch of caddis flies flying low over the water, don’t stop until you find the place where they actually dive or dip into the water. They may not be doing it all over the river. Midges seem to prefer medium-fast water for laying eggs.
I’m not so much telling you to look for particular water here as I am urging you to move around. A lot. Especially if you see insects on the water. If you don’t see signs of fish feeding, it might be that you’re not in the place where most of the insects are hatching or mating. Perhaps the fish in the pool you are standing in may not pay as much attention to hatches. Regardless, pull on the oars and head downstream until you find feeding trout, or, if you are on foot, move your butt. On foot I always agonize over whether I should wait to see if maybe the fish will feed when the hatch gets heavier. Or maybe I should look upstream. But what about downstream? I can’t give you concrete answers on these questions, but I can tell you I’ve had more success moving around and looking for feeding fish as opposed to sitting on the bank waiting for things to happen.
Here’s an example: Bob Gotshall and I sat on the bank of a favorite pool on the Henry’s Fork in Idaho. We had taken some nice fish on dry flies the previous few days. We sat there for five hours, pondering the meaning of life and how finicky the river’s rainbows were that day. We saw nothing rising and few insects. I took some pictures and generally amused myself by monkeying with my leader taper, making slight modifications and testing it on the fishless water. Bob took several naps. In midafternoon, a guy on a bicycle wearing waders pedaled by us. As he passed, he told us the Green Drake hatch a half mile upstream had been tremendous and he had taken several of the river’s big rainbows on dry flies. Of course we immediately bolted upstream as quickly as two sixtysomething guys in waders could move in hot weather, but by the time we got there it was all over.
Trout prefer to lie in water that runs about one or two feet per second. In a uniform current that runs at this velocity from top to bottom, trout will just suspend below the surface, not resting on the bottom. Here they are comfortable hovering in the current as long as there are enough insects drifting to hold their interest. You find this kind of water in the tails of pools, in the slow middle water in a pool, or in whirlpools (or “recirculators,” as they’re called on some Rocky Mountain rivers). How fast is one foot per second? You can measure it off if you want, but it’s about the speed of a slow walk and once you’ve spent enough time fishing hatches you’ll recognize the right speed.
If trout can’t find a place where they can suspend and feed, or if there are not enough insects drifting there, they’ll find water in that comfortable velocity but adjoining faster water that brings a reliable supply of food. The comfortable place could be on the bottom of the river, in a small depression that lowers current speed, or near a rock or jumble of rocks that break the current. The fish observe from this comfortable spot and dart up into the faster water to spear an insect from the surface or intersect one drifting below the surface. This is the classic type of rise as most of us envision it.
One of the best places to find fish feeding on hatches is along banks. You won’t find trout near a bank with fast current slamming against it, nor will you usually find trout along banks with large expanses of shallow water. Look for banks that have faster current a foot or two out from the bank, a shallow shelf that drops into deep water, and projections along the bank. Large rocks, logs, or just little points of land are all projections that hold trout. These projections break the current and form that comfortable speed trout prefer. Trout feeding along banks will tip straight up to capture an insect if there are enough in the slower water, but in sparser hatches you’ll see trout lying in the slower water along the bank, darting a few inches out into the current when the right insect drifts by.
Pocket water (water with lots of large rocks and foamy current) can fool you. Because of all the turbulent water, much of it looks too fast to hold trout. Yet if you look carefully, you’ll see that much of this water—in front of rocks and along their sides, plus places close to the bank—is actually very slow. Because fast water is never very far away, trout find comfortable places in pocket water to feed on hatches. They also feel comfortable here because they are never far from a safe place to hide alongside a rock or in foamy water. An added bonus to fishing this kind of water is that rises are tough to see so most people pass it up during a hatch. Pocket water often holds surprisingly large fish.
Riffles are also deceiving during a hatch. They look too shallow and too fast to hold fish, but many places in riffles are not. And like pocket water, rises in riffles are hard to spot and may go unnoticed by other anglers. When you look at a riffle, you see a wide expanse of what appears to be fast, uniform water. But that’s seldom the case. Riffles don’t flow over a completely flat sheet of bedrock. Gravel and rocks deposit in some places and get washed out of others, and as a result riffles often have deeper pockets that offer trout enough depth for protection from predators. The deeper depressions also slow the current for two reasons. One is that the current volume fills a larger space, so energy is decreased and water velocity slows. Just as important is the turbulence that forms as faster water sweeps over the slower water below. Tiny vortices move the current in every direction, and this redirection of flow slows the downstream progress of the water.
Look for darker spots in riffles where you can’t see the bottom. The surface will also have a slick appearance due to the slower current. A spot the size of a kitchen sink is probably not enough to hold a trout—or several trout—but when you find a pocket in a riffle that’s the size of a compact car and is at least two feet deep, there is a potential for trout.
If I had my choice as to where I could fish for trout feeding on the surface, my favorite place would be one of these hidden pockets in a riffle. Trout here are always more tolerant of your approach. They feel more comfortable in broken water. They don’t get a good look at your fly because of the broken surface so they are easier to fool. And when they get hooked, they have nowhere to go except deeper water that might be 50 yards away and they often go airborne on the way. None of that bulldogging in deep water looking for a log to break your connection to them.
One of the hardest times to discover trout feeding on hatches is in spring when runoff swells the river. Most of the places that will produce fish later in the season are too deep for fish to battle the current for surface food. And surface currents even in slower areas can be too fast. I’ve watched rivers daily in the spring, not seeing any rises even though the water was covered with hatching insects. As the water drops daily, you’ll suddenly find the magic day when some of the surface currents are slow enough to make feeding on hatches comfortable for trout, and from then on, unless it rains and raises the level of the river, you’ll find trout responding to hatches. At first you will see them in slow back eddies, along banks with slower current, and in the middle of slower, deeper pools. As the season progresses and the water drops, you’ll gradually see them feeding on hatches in successively faster water.
When you do encounter water that seems too fast for trout feeding, it’s even more important that you move around. If there are abundant insects on the water, sooner or later you’ll find the right current speed. I remember one day when the Battenkill was swollen but Hendrickson mayflies carpeted the water. I spent the entire Hendrickson hatch, from 2:30 to 5:30 p.m., driving to different pools and then walking the banks looking for rising trout. Finally, on my way home, I stopped at some very slow water in the upper river and found a group of brook trout rising to small olive mayflies. It took all day, but I finally found some dry-fly fishing.
Tom Rosenbauer’s The Orvis Guide to Hatch Strategies is available online, in Orvis store, and in bookstores everywhere.