Banjo Music Courtesy of Banjo HangOut -- That white line in Lake Mead is not a twenty year fill line, it's from the original fill in 1938, Yes, there has been a twenty year lowering, blame it on Lake Powell, up stream of Lake Mead which doubled the artificial lake surface of The Colorado River. Which means twice the surface exposed to evaporation. FYI/ The Colorado River is the steepest water shed in America.