Topographically, Malawi lies within the Great Rift Valley system. Lake Malawi, a body of water some 580 km (360 mi) long and about 460 m (1,500 ft) above sea level, is the country's most prominent physical feature. About 75% of the land surface is plateau between 750 m and 1,350 m (2,460 and 4,430 ft) above sea level. Highland elevations rise to over 2,440 m (8,000 ft) in the Nyika Plateau in the north and at Mt. Sapitwa (3,000 m/9,843 ft). The lowest point is on the southern border, where the Shire River approaches its confluence with the Zambezi at 37 m (121 ft) above sea level.