Kachess River is a tributary of the Yakima River, in the U.S. state of Washington. From its source on Chickamin Ridge in the Alpine Lakes Wilderness region of the Cascade Range, the Kachess River flows south into Kachess Lake, a natural lake regulated as a reservoir by Kachess Dam. Below the dam, the Kachess River flows south and then empties into the Yakima River at Lake Easton.