Alder Lake is a long reservoir on the Nisqually River about ten miles south of Eatonville, Washington, It was created by the construction of Alder Dam by Tacoma Power in September 1944. At the very eastern end of the lake is the town of Elbe, Washington.
The name of the lake recalls the former small town of Alder, which was flooded in 1945 by the impounded water of the lake and disappeared. The extinct town, in turn, was named for alder trees near the original site. The current community of Alder is located north of the lake.
In 2021, Intel gave its 12th generation Intel Core processor the codename Alder Lake after the body of water.