Fish are driven into the drop-off areas by birds of prey and boat traffic. The drop-offs shelter fish from these annoyances. The deep areas adjacent to the shallows furnish fish easy access to their food supplies. Consequently drop-offs can be highly productive during bright light conditions.
I prefer a sunken retrieve which travels my fly up from the depths along the slope of a drop-off. As the fly travels it becomes more visible to the fish.
In clear water, drop-offs are easily seen by noting the water’s color change from deep blue to a lighter green. In stained water, video sonar can help locate the drop-off areas.