Seeing into the river is a learned skill. It takes a lot of time on the water to judge the three dimensional flow of a river. Reading the surface is easy. Even without bubbles on the top, most anglers quickly learn to gauge the speed of the top current in relation to their fly or indicator. But what lies beneath can be unpredictable and deceiving. Eventually, with the help of polarized lenses and some serious thought, experienced anglers become proficient (enough) in reading the currents below.
But where does it begin?
Understanding a little about the water column and the correlating habits of trout goes a long way toward better fishing. So let’s do it . . .
Top to Bottom
Fast and slow. This is a simplified view of the water column. It’s fast up top and slow near the bottom. Water near the streambed is bumping into a lot of things down there: tree parts, rocks, vegetation and trout! And constantly crashing into things will slow anything down.
By contrast, the middle current encounters no obstacles. It clips along at a higher rate because it makes no stops, because it doesn’t need to flow around many things.
You might think the top current would flow fastest. But the surface also has an obstacle to rub against — the air. And in fact, on windy days, you can see this displayed pretty dramatically with a light dry dropper rig. The nymph is often downstream of the dry rather than trailing behind it as expected. Again, time on the water teaches all of this.
From a fisherman’s perspective, the top current is fairly close in speed to the mid-current. And that holds true often enough. The important distinction is just how dynamic the difference can be between the bottom current (something we can’t see) and the surface (something we can).
Accurately estimating the speed of the bottom current is critically important. Because our trout are usually sitting down in that strike zone.
The Strike Zone
Trout are predictably efficient. And this is a key trait to understand. They rarely expend more energy than necessary. Looking for easy meals, they maximize their motion for the highest calorie return. This is instinct, of course, and not a thought process. But trout habits can be patterned, simply because these instincts are embedded deep into the genes of every trout. Furthermore, most of what we learn to expect from trout, season after season and day after day, is based on their tendency toward efficiency. Think about that.
And one of their most predictable habits is where a trout will be in the water column.
I refer to the cushion of water near the streambed as the strike zone. Because, often enough, this is our target water below. Trout station themselves in the slower currents, conserving energy and feeding on nymphs, crustaceans or baitfish. All of these life forms use the slower currents near the bottom to their advantage. And most of what happens on a river — most of the life — takes place on or near the bottom. In turn, this is a primary target for our flies.
Trout love the bottom, but they rarely hold in the middle. They may target emerging insects or pick off a stray baitfish mid-column, but they are most often holding below.
At times, we find them slurping spinners at the top, cruising the first few inches below the surface and picking off one bug after the other. But trout need a good reason for this. They need a high concentration of food at the top, and/or slow currents — soft enough to waste no energy by holding just under the surface, and protected enough not to feel threatened.
How deep is this strike zone?
That depends. How big are the rocks? How chunky are the tree parts? Larger objects slow the currents more dramatically and create a taller strike zone.
On my home water, the average rock is fist-sized or smaller. It’s an easy stream to wade, and the streambed is fairly predictable. In most of its sections the strike zone is about eight inches tall and not much more.
But on one of my favorite big rivers, the average rock is the size of a twenty watt guitar amp. It’s a river full of beach ball sized boulders, mixed in with much larger chunks of limestone. The wading here is unpredictable at best, and it’s a difficult wade if you don’t know the river. Here, the strike zone is regularly a foot tall and up to eighteen inches. The larger rocks and sunken hemlock trunks provide a deeper cushion of water — a wider strike zone — for trout holding near the streambed.
If you’re a dry fly guy, you read the surface. And you might not care much about the rest of the water column. Fair enough.
But the angler who presents flies under the water, be it nymphs, wets or streamers, will catch trout more consistently by considering the strike zone.
In the companion article to this one, I work through some ways to read this cushion of water and to fish it with more accuracy. Because unless you find some willing trout near the surface, you need to hit the strike zone to hook up regularly. And guessing the depth and speed isn’t nearly as productive as reading the strike zone and accurately drifting through it.
Enjoy the day.
T R O U T B I T T E N