Dangqu

The Dangqu, Dam Qu (Chinese: 当曲, pDāngqū) or Dam Chu (Tibetan: འདམ་ཆུ, w'Dam Chu, lit. "Marshy River") is the longest source of the Yangtze River, with a total length of 365.7 km (227.2 mi) located in the Qinghaiprovince of the People's Republic of China. It runs from its source in an eastern offshoot of the Tanggula Mountains (唐古拉山), receives its main tributary the Buqu-Gar Qu River (布曲), and has a confluence with the Ulan Moron, where the Tongtian River is formed. The Dangqu has been discovered to be the actual and the longest headwater of the Yangtze River under modern criteria, although the nearby Ulan Moron or Tuotuo was traditionally regarded as the primary river of the two.