 The river is joined by many tributary streams including Waptus River and Cooper River, after which it enters Cle Elum Lake.Although a natural lake, Cle Elum Lake's water level and discharge is controlled by Cle Elum Dam, a 165-foot (50 m) high earthfill structure built in 1933.The dam and lake are managed for irrigation purposes by the United States Bureau of Reclamation as part of the Yakima Project.