This photo shows erosion caused when overflow water cascaded down the emergency spillway of Oroville Dam, Monday, Feb. 13, 2017, in Oroville, Calif. Water levels dropped Monday at the nation's tallest dam, easing slightly the fears of a catastrophic spillway collapse that prompted authorities to order people to leave their homes downstream. At upper left, water flows down the dams main spillway. (AP Photo/Rich Pedroncelli)