Before the filling of Lake Powell (a reservoir of similar size to Lake Mead) behind Glen Canyon Dam, the Colorado River flowed largely unregulated into Lake Mead, making Mead more vulnerable to drought. From 1953 to 1956, the water level fell from . During the filling of Lake Powell from 1963 to 1965, the water level fell from . Multiple wet years from the 1970s to the 1990s filled both lakes to capacity, reaching a record high of in the summer of 1983.