Between your fingers you hold a stone and throw it into flowing water. The effect might not be easy to see. There will be a small ripple where the stone breaks the surface and then a splash, muffled by the rush
of the surrounding river. That’s all.
Throw a stone into a lake. The effect will be not only visible but also far more lasting. The stone will disrupt the still waters. A circle will form where the stone hit the water, and in a flash that circle will multiply into another, then another. Before long the ripples caused by one plop will expand until they can be felt everywhere along the mirrored surface of the water. Only when the circles reach the shore will they stop and die out.
If a stone hits a river, the river will treat it as yet another commotion in its already tumultuous course. Nothing unusual. Nothing unmanageable.
If a stone hits a lake, however, the lake will never be the same again...