I get this question a lot: how do I know if my fly presentation is drifting naturally?  Well, there is a lot that goes into answering that question but one of the biggest determinants is – is your presentation drifting downstream in a relatively straight line? I call this the straight line theory and it applies to both dry fly and nymph fishing.

It looks unnatural whenever your flies do not drift straight downstream with the current because aquatic insects generally drift straight downstream. With the exception of a few nymph species, almost all aquatic nymphs cannot swim sideways throughout the water column. When currents dislodge a nymph from its resting place, the majority of nymphs are forced to drift helplessly downstream wherever the currents take them. When nymphs emerge from the bottom to the surface to hatch into adult insects, the majority of nymphs rise straight up from the river bottom as they drift downstream.  Even adult aquatic insects drift straight downstream with the current as they dry their wings on the river’s surface and try to fly into the air.

Now that it is clear that the majority of aquatic insects in all life stages generally drift straight downstream, the straight line theory means that your flies should drift straight downstream from their starting position to look natural. For example, if you casted upstream of your standing position and about ten feet outward, your flies should remain ten feet outward as they drift both in front, and below you. You can achieve a straight downstream drift in two ways: by raising and lowering your rod tip or by mending your fly line upstream or downstream. Not all currents drift perfectly straight downstream and you technically want your flies to drift in the same current lane they started in, but more or less currents drift straight downstream so the straight line theory is what you should strive for.

Raising and lowering your rod tip will help your flies drift in a straight line downstream when casting short distances. After you cast upstream and as your flies drift downstream back to your standing position, slowly raise your rod tip up to take the slack fly line off the water. Once your flies are directly in front of your standing position and begin to drift below you, slowly lower your rod tip to give out fly line. If you do not raise your rod tip as your flies drift downstream toward you, excess fly line would drag on the water and pull your flies sideways through the currents. If you do not lower your rod tip as your flies drift downstream below you, tension would increase on your fly line and pull your flies sideways through the currents.

Mending your fly line upstream or downstream will help your flies drift in a straight line downstream when casting long distances. The direction you mend your fly line depends on the speed of the current between your standing position and the area you are targeting. However, faster water is normally between you and the target area so I will address this more common occurrence.  When you cast upstream, mend your fly line upstream. This action will give some slack to your fly line so that the current doesn’t pull your fly line sideways across the water’s surface. Once your flies drift directly in front of you, your flyline should be about straight. As your flies drift below your standing position, mend your fly line upstream again. This action will again give slack to your fly line so the current does not pull your flies sideways through the water.  Don’t be afraid to mend your fly line several times in a drift; I sometimes have to mend my fly line three or four times in a single drift to keep it drifting in a straight line downstream.

More information on trout nymphing can be found in my guide book SIMPLE NYMPHING FOR TROUT IN RIVERS & STREAMS.

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