Kachess Lake is a lake and reservoir along the course of the Kachess River in Washington state, USA. The upper part of the lake, north of a narrows, is called Little Kachess Lake. The Kachess River flows into the lake from the north, and out from the south. Kachess Lake is the middle of the three large lakes north of Interstate 90 and the Yakima River in the Cascade Range, the other two being Keechelus Lake and Cle Elum Lake.