Which sentence summarizes a central idea in “A Scratch Tells All”?

Edward Abbey says that Lake Powell which is formed by Glen Canyon Dam is not a lake but is a reservoir.This means that there is a constantly fluctuating water level based on the power needs of the system that the Dam is connected to. Also this power need is primarly focus of the orchestrators of the dam not the recreational possibilities that they publicize. The drastic change of environment around the river, and the continuous changes of water level, had huge negative impacts on wildlife that were settled near it. The only thing noticeable around the edge of the water is the bathtub ring left by the change of water level.