Kachess Lake, Reservoir in Kittitas County, United States

Kachess Lake is a natural lake in Kittitas County, Washington, enlarged by the 35 m high Kachess Dam, an earthfill structure built in 1912. The lake stretches about 17 km and covers 18.6 km², with a narrows separating the upper Little Kachess Lake. The Kachess River enters from the north and exits south through the dam.

Kachess Lake is a natural lake whose level is controlled by Kachess Dam, a 35 m earthfill structure built by the Bureau of Reclamation between 1910 and 1912 on a glacial moraine as part of the Yakima Project. A 877 m discharge channel was cut from the lake to the dam's outlet works, about 550 m downstream and lower than the original outlet, adding 76,000 acre-feet of storage. Active capacity is 239,000 acre-feet.

The name Kachess comes from a Native American term meaning "more fish", contrasted with Keechelus Lake, whose name means "few fish". The lake lies in Wenatchee National Forest, and anglers today catch kokanee, cutthroat trout and rainbow trout in its water.

The lake is accessible for fishing throughout the year, though visitors should be aware of local regulations. During warmer months the water level drops noticeably, which can affect the use of boat launch facilities.

Kachess is a natural lake, not a flooded valley: its outlet was lowered by a 2,877-foot discharge channel built to the dam's outlet works, about 1,800 feet downstream, so an extra 76,000 acre-feet of runoff could be stored. The gravel spit and small rocky island in the lower left of the view sit in the drawn-down reservoir zone.