Understanding Stream Flow To Improve Nymphing Success
Trout don't move very far from their preferred location when feeding on drifting nymphs. This means that if you want to be successful, your nymph has to be "spot on" the feeding lane, both from side-to-side and right at the feeding depth. Nymph in the feeding lane, takes. Nymph out of the feeding lane - try again.
Getting the right lateral or side-to-side drift of your nymph through the feeding lane, while not always simple, is not terribly hard. For one thing you know where that feeding lane is. Just follow the foam line. And you know where you want your nymph to be by watching the indicator. If your indicator is not drifting the nymph where you want it, a few subtle mends should position the indicator in the feeding lane. Making sure your nymph is drifting at the right depth is another issue.
A basic understanding of how water flows in a stream channel will help you understand what it takes to get your nymph down to the trout's level. The first thing you need to know and understand is that the speed at which the water is moving, called the velocity, is not the same throughout the stream. A generalized view shows that the velocity is greatest in the middle and just below the surface.
The variation is primarily due to the friction from the sides and bottom of the stream channel on the water molecules flowing by. This vertical velocity distribution is why trout can live and grow in water that looks like it is moving too fast. At the location where the trout are holding, the velocity is near zero!
You also have to consider the sinking rate, or settling velocity, of your nymph relative to the water velocity. There are two important considerations in the sinking rate of your nymph. The first is the drag or resistance of the leader and the nymph. The second is the weight and density of your nymph. With this understanding of stream flow and sinking characteristics you can take a few simple actions to improve our nymphing success.
Don't Use a Tapered Leader: The first time most fly fishers here this suggestion they think it is heresy. You need that tapered leader to get a smooth turn-over and delicate presentation. How far do you cast when you are nymph fishing? Not very far. And, generally it is with a weighted nymph. It is flipping or chucking, not artful casting. Since the most successful locations for nymphing are riffles, pockets and shoals, a delicate presentation isn't needed. You have to get your nymph all the way down to the trout's holding position near the stream bottom. While it may not seem to be important, the thickness of the upper portions of a tapered leader cause significant drag and resistance to the sinking of your nymph. Since you don't need the tapered leader for presentation, why use one at all? Try just using 8 to 10 feet of whatever sized terminal tippet material you would use as your leader. Drag and resistance will be greatly reduced and your sink rate increased.
Reduce The Surface Tension of Your Leader: One of the primary reasons that a leader floats is because it of the water's surface tension. That is the force that keeps it from sinking. A major contributor to the surface tension is body oils from handling the leader. You can buy products designed to reduce surface tension and help your leader sink, or you can use the isopropyl alcohol pads they sell for cleaning your eyeglasses. Simply pull your leader through the pad and let it dry for a few seconds. If you don't have any alcohol pads, find a backwater area and grab a bit of fine silt and organic material. Run your leader through it. It's not as good as the pads but it does help.
Start With The Indicator 1.5X The Water Depth: Unless you are fishing an extremely heavily weighted nymph in shallow water, it is not very likely that you nymph will hang straight below your indicator. Almost always there will be a bow in the leader. The faster and deeper the water, the greater the bow will be. Placing your indicator on the leader at 1.5 X the water depth is a good place to start, but make adjustments to the distance between the indicator and the nymph until the fly is at the depth you need. It is better to have more distance than needed between the indicator and the nymph than not enough distance between the indicator and the nymph.
Cast Upstream of Where The Trout Will Be: Even with a heavily weighted nymph and a straight leader, it will take some time for the nymph to sink down to the trout's depth. Cast far enough upstream to make sure that your nymph has plenty of time to sink and gets down to where the trout is holding. It is far better to have your nymph bouncing along the bottom upstream of the fish, than to have your nymph float by over his head!
Make An Immediate Upstream Mend Of The Indicator: This can't be stressed enough! Remember that the water velocity or speed is so much greater on the top than it is on the bottom. Without getting the indicator upstream of the nymph, the indicator, floating in that high velocity water at the surface, will pull the nymph along and not give it an opportunity to sink. As soon as the indicator hits the water make a quick mend to move the indicator upstream of where the nymph landed in the water. This gives the nymph a few seconds to start to sink before being pulled along by the indicator. As the indicator starts to overtake the nymph, make a second upstream mend of the indicator. Make additional upstream mends as necessary.
You will find that just this basic understanding of how stream flow effects the movement and location of your nymph will have a significant impact on your nymph fishing success. The more trout that see your nymph in their feeding lane, the more trout you can catch.