Lake Chelan is a narrow, 50.5 mi (81.3 km) 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 (2.1 km). Near its upper end, the lake surface lies more than 6,600 ft (2,000 m) below peaks less than 3 mi (4.8 km) 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 (6.4 m) to its present maximum-capacity elevation of 1,100 ft (340 m).

Chelan County is a county in the U.S. state of Washington. As of the 2020 census, its population was 79,074. The county seat and largest city is Wenatchee. The county was created out of Okanogan and Kittitas Counties on March 13, 1899. It derives its name from a Chelan Indian word meaning "deep water," likely a reference to 55-mile (89 km)-long Lake Chelan, which reaches a maximum depth of 1,486 feet (453 m).