Adam Clarke on 2 Kings 3:22

Saw the water on the other side as red as blood - This might have been an optical deception; I have seen the like sight when there was no reason to suspect supernatural agency. The Moabites had never seen that valley full of water, and therefore did not suspect that their eyes deceived them, but took it for the blood of the confederate hosts, who they thought might have fallen into confusion in the darkness of night and destroyed each other, as the Midianites had formerly done, Jdg 7:22, and the Philistines lately, 1Sam 14:20.