Sanjiangyuan National Nature Reserve, high plateau region of Qinghai containing the headwaters of Changjiang or Yangtze, Huanghe or Yellow River and Lancang or Mekong River
Definitions (Wiktionary)
name
Sanjiangyuan (an area of the Tibetan Plateau in Qinghai, China, which contains the headwaters of the three great rivers of Asia: the Yellow River, the Yangtze, and the Mekong)