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Depth of Presentation

By Scott O’Donnell


When I’m swinging a fly for steelhead my mind is fully consumed with the image of where my fly is and what it’s doing. How deep is it? Is it sinking, rising up, or holding its depth? I try to picture it as it stalls in an eddy behind a boulder, then suddenly speed downstream until it whips around to hang still in the seam between the eddy and the main flow, all the while trying to keep a grasp on how deep the fly is.

The closer an angler can get their fly to the same depth as the fish, the more fish they’ll catch. There are exceptions to that, but where I’ve fished, the exceptions are rare. There are other factors too – like the speed in which the fly is traveling, and the fly pattern. Depth, I think, is by far the most important.

Imagining what the fly is doing is one thing, being accurate with the assessment is quite another. It’s a very difficult task. There are a number of different factors involved. Not the least of which is knowing the water being fishing. Having a clear picture of the depth and structure of the run being fished is paramount. The only way to really know is by actually having seen and studied the water when the river is low and clear. If you haven’t, if you’re unfamiliar with the run’s depth and structure, then you’re forced to rely on your ability to “read” the water. Reading water is a priceless skill to have, but far from flawless.

I consider myself good at it and yet I couldn’t begin to count how many times I’ve been wrong. Many times I’ve fished through an unfamiliar run, confident that my fly was within a couple of feet of the bottom, only to float over it afterwards and find out that the water was much deeper (or shallower) than I thought. In many cases I hadn’t even given myself a chance of catching a fish, but I’ll chalk it up to dues paid and a valuable learning experience.


When you add the infinite number of possible combinations of sink tip lengths and sink rates, length and diameter of leaders, and the sink rates of flies to this already complex formula, it becomes obvious that the art of imagining exactly what the sunk flies are doing can never fully be mastered.

While I’m imagining where and what my fly is doing I’m also CONTROLLING it! This is the most important part. I control it by my choice of sink tip-leader-fly combination, by choosing which angle I’m going to cast (straight across, quarter down, etc.), by mending (upstream, downstream, both, when to mend, and how much), and by how much tension to apply to the line with my rod.

I could go on and on about this topic and believe me, I’d love to, but I think I’m getting close to my word count quota here. Maybe this topic is just a little too deep for a blog post (pun intended). I’ll finish with this – if you haven’t already, buy a set of RIO’s Skagit MOW Tips (it’s all you’ll ever need to cover any situation). Learn how varying your leader’s length and diameter effects depth, and carry a wide range of flies from buoyant to super fast sinking.

The next time you’re fishing a run that you’re not totally familiar with, find the bottom and then make the necessary adjustments until you can imagine you’re fly fishing between eighteen inches and two feet from the bottom and you’ll catch MOW fish! (Sorry, couldn’t stop myself).


The next thing to understand is how the line/leader/fly combination interacts with the current flow. A great way to start learning this is to fish a dry or waking fly that you can actually see (rather than imagine) and watch what it does in different current situations. I had fished a sunk fly for several years before I tried my hand at dry fly fishing. I realized immediately that my wet flies weren’t always doing what I thought they were. It was huge for me. Translating this knowledge to the sunk fly does get a bit tricky because of the added dimension of depth.

When fishing a dry fly an angler needs only be concerned with the surface currents as they vary (or not vary) across the width of the river. With a sunk fly you need to add the varying currents that exist from the surface to the river’s bottom. Surface current is always faster than the current near the bottom. This is important because it the sunk fly is traveling slower than the line you see swinging across the river. This is called “lag”. A small amount of lag is very helpful in getting a fish hooked in the corner of its mouth. Too much lag can lead to dragging the line across the fish and can speed the fly past the point of being effective.