Water has been recognized as an important resource in central Arizona and has affected populations occupying the Salt River Valley for centuries. Water related activities have been documented since about 200 before the common era, when Hohokam Indians settled the Valley and constructed canals to irrigate their fields. Europeans began to settle in the Phoenix area in the late 1860s and depended on irrigation water from the Salt River for agriculture. However, water supplies fluctuated greatly because the river often flooded in winter and dried up in the summer. There were no impoundments to store water for the dry seasons. In 1904, the Salt River Water Users' Association signed an agreement with the United States government under the National Reclamation Act to build a dam on the Salt River below the confluence with Tonto Creek. The Roosevelt Dam, the first of 6 dams on the Salt and Verde Rivers, was completed in 1911.