Just as the taller rock creates a surface wave, the pothole, bucket or depression in the riverbed has a corresponding feature on the surface. It’s a flatter, calmer piece of water — smoother than the surrounding surface currents. Is it harder to recognize? Sure it is. It’s also not as reliable of a sign. But quite often, if you find a calm piece of water, surrounded by mixed currents and minor waves, a pothole lies below.
Be careful what you’re reading, though. The stall, or slower piece of water that lies just downstream of every rock, is not the same thing as a pothole — not at all . . .