The Water Column — And the All-Important Strike Zone

by | Jul 17, 2019 | 12 comments

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.

Water flows fastest near the top and slowest near the bottom. The strike zone is a cushion of water on the bottom where most life in a river happens. It can be a few inches tall or a couple feet tall, depending on the obstructions at the bottom of the river.

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.


Who cares?

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.

READ: Troutbitten | Forget the Bottom — Glide the Nymphs Through the Strike Zone


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Enjoy the day.
Domenick Swentosky


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Domenick Swentosky

Central Pennsylvania

Hi. I’m a father of two young boys, a husband, author, fly fishing guide and a musician. I fish for wild brown trout in the cool limestone waters of Central Pennsylvania year round. This is my home, and I love it. Friends. Family. And the river.

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  1. The picture of the moss covered boot is awesome. It is always weird when you find a shoe in the middle of nowhere, like how do you lose a shoe and not put it back on? Wss there a struggle? Is there a body near by? Since I was a little kid whenever I found a shoe in the woods it always creeped me out. Very haunting.
    Looking forward to part 2.

    • Right on. When I was real young I found a few things like that in our back woods. I made up all kinds of stories in my head.

  2. I had to rethink a number of things I thought I knew because you referred to the bottom as the strike zone. I am looking forward to this series of articles. Thank you Domenick.

    So I think, if fish are getting enough easy food in the bottom strike zone, do they ever look up? I think I encountered this on the stream with my daughters a month ago. So much water and food down low, kept the trout feeding under the surface and ignoring the “hatching” insects for the most part.

    My daughter swinging minnow pattern through the riffles above, was getting a few fish. My other 2 daughters in the slow deep pockets below where the fish usually rise to the “hatch,” only got one take. Looking back I wish I would have had all my daughters swinging the riffle above.

    • HI Rick,

      Great thoughts there.

      Right on. If trout have so much food below, they need a real good reason to come up. I believe that’s why these trout waters I fish are so excellent, really. They are packed with food opportunities down below. So trout don’t NEED to expose themselves by coming to the top or even mid column. They can hang on the bottom and feed year round.

      That said, there are plenty of times when our trout also feed at the top or middle — it just takes the right opportunity for them to do it. And it’s our job as good anglers to recognize what the trout are usually doing and when they are doing something out of the ordinary.



  3. Looking forward to this series Dom. You

    • Cheers, Nick.

  4. Wanting more, more info about strike zone. Looking forward to Part 2. Keep on rolling.

  5. I look forward to the next article.

    Since the water I fish has very few hatches, the fish mainly stay near the bottom water cushion eating a lot of small stuff. There are many ways to fish that zone, but one of the best is either using a drop shot rig or a heavy point fly with a small dropper tied fairly close to the point fly (so that it effectively rides in the cushion).


  6. When I used to only fish dry flies, if I didn’t have any action, I just assumed the fish weren’t feeding. Once I began nymphing, I realized how ignorant that idea really was.

  7. Love this article, very helpful – thank you Dom!

  8. For me, this idea is why I tight-line nymph in the first place – to get my flies in the strike zone as consistently as I can while being in contact with them. When you get that perfect drift, your tippet penetrating the faster water and getting your flies to the strike zone, everything seems to slow down for a moment. It’s weird. Your senses are piqued, your awareness is elevated, becuase you know a fish is about to grab your fly. Can I get such a drift all the time? No. Not even close, but I can usually tell when my flies are in the zone and when they’re not. So I got that going for me, which is nice. 🙂


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