The nymph is no different than any other type fly - presentation is still more important than pattern choice. The nymph, for optimum effect, has to drift at the eye level of the trout. When fish are feeding on items near the bottom, a drift a few inches over their heads makes the best looking fly mediocre and a drift a foot over their heads makes the best looking fly worthless.

It is easy to imagine insects, scuds, worms and eggs in the currents, filling the water column top to bottom. In reality objects caught in the flow concentrate in a narrow mixing zone. Entomologists estimate that 70 to 80 percent of free-drifting life forms move at any given moment in an interface between the dead water of the rocks and the unobstructed water of the open flow. This turbulent band, with its circling eddies, tenaciously holds organisms until they reach an area where the flows are slow enough for them to settle to the bottom.