Located in Gongbo'gyamda County, Basong Tso is a holy turquoise coloured alpine lake located in the middle and upper reaches of the Ba River, which is the largest tributary of the Nyang River (the longest tributary of the Yarlung Tsangpo River). It belongs to the Nyingma school of Tibetan Buddhism and is the only national 5A level scenic spot for natural scenery in Tibet. The lake is mainly turquoise in colour but depending on the angle of the sunlight it magically changes to blue, light blue and sapphire accordingly.