Yangtze River above Yushu.
According to the Chinese Academy of Sciences, the true source of the Yangtze is the headwaters of the Dam Qu, near the southwestern border of Qinghai (32.544722°, 94.380000°, 17,500'). A CAS team rafted this tributary in 1986.
The stretch from the bridge near Qumarleb (34.028082°, 95.820942°, 13,650') to the bridge near Yushu (33.006914°, 97.247625°, 11,600') was run commercially in the mid 1990's by Earth River Expeditions (www.earthriver.com) and by Last Decents River Expeditions since 2006 (www.lastdescents.com). The gradient of this 200 mile sections is about 15' per mile and it is characterized by abundant wildlife, spectacular scenery and multiple Tibetan monasteries. Flows range from a few thousand cfs in early summer to ten to twenty thousand cfs in mid summer. It becomes Class 4 during very high flows. Due to the high elevation, it is only feasible to run this stretch from May to September. A video of an expedition run by Last Descents in 2006 is available.
Just above Yushu, the Chinese are planning to build a dam that will divert water into a series of tunnels and canals into the headwaters of the Yellow River.