"Reach 1: Lancang Jiang or Upper Mekong River in China". In this part of the river, the major source of water flowing into the river comes from melting snow on the Tibetan plateau. This volume of water is sometimes called the "Yunnan component" and plays an important role in the low-flow hydrology of the lower mainstream. Even as far downstream as Kratie, the Yunnan component makes up almost 30% of the average dry season flow. A major concern is that the ongoing and planned expansion of dams and reservoirs on the Mekong mainstream in Yunnan could have a significant effect on the low-flow regime of the lower Mekong basin system.