Rapids are a place of extremes -- extremes in water depth, extremes in bottom erosion, extremes in even current speeds, as we shall see. Rapids are always better places to be searched carefully by the fly fisher -- carefully in terms of wading, and carefully in terms of making certain that no good water goes unexplored.
Rapids are tough places to put a fly down and expect it to float with any sort of dead drift. But there are some tricks to it. First comes reading waters, then comes the fishing. In all rapids, there is a "secret river". It may be quite narrow, and then again it may be fairly wide. It's the easy water, the place one can toss a fly without much need to do more than use a Harvey-style leader to get a good float. During the salmon fly hatch [on Montana's Madison River] (and every other hatch for that matter), the fishing can be fast and furious in the secret river, and it's the first place I hit. It's the water right against the bank -- you know, that stuff one wades through to get out there into the "real" river. But think about it for a moment: Where's the best place for an energy-conserving trout to park itself while getting food in the easiest fashion? That's right: In the slow water next to the shore where the stoneflies are hanging on every bush like overly ripe fruit.
When guiding anglers on the Madison, my long-time friend, Mike Lawson, tells clients to cast into all those places where one wouldn't normally fish -- in other words, the secret river. Those that pay attention to his advice find out very quickly that Mike is a shrewd water-reader, indeed. Most anglers use the secret river as their wading lane, when in fact, it should be their fishing lane.