Lake Manasarovar lies at 4,556 m (14947.5 ft) above mean sea level, making it the highest freshwater lake in the world. It is relatively round in shape with a circumference of 88 kilometres (55 mi). Its depth is 90 m (300 ft) and its surface area is 320 square kilometres (120 sq mi). The lake freezes in winter and melts only in the spring. It is connected to nearby Lake Rakshastal by the natural Ganga Chhu channel. Manasarovar is the source of the Sutlej River which is the easternmost large tributary of the Indus. Nearby are the sources of the Brahmaputra River, the Indus River, and the Karnali River(Ghaghara) which is an important tributary of the Ganges River, so this region is the hydrographic nexus of the Himalaya.