Lake Chelan is a narrow, 50.5 mi long lake in Chelan County, north-central Washington state, U.S. It is an overdeepened lake and resembles a fjord, with an average width of 1.3 mi. Near its upper end, the lake surface lies more than 6,600 ft below peaks less than 3 mi away. Before 1927, Lake Chelan was the largest natural lake in the state in terms of both surfa…Lake Chelan is a narrow, 50.5 mi long lake in Chelan County, north-central Washington state, U.S. It is an overdeepened lake and resembles a fjord, with an average width of 1.3 mi. Near its upper end, the lake surface lies more than 6,600 ft below peaks less than 3 mi away. Before 1927, Lake Chelan was the largest natural lake in the state in terms of both surface area and water volume. Upon the completion of Lake Chelan Dam in 1927, the elevation of the lake was increased by 21 ft to its present maximum-capacity elevation of 1,100 ft.