The Limpopo River rises in South Africa and flows generally eastward through Mozambique to the Indian Ocean. The term Limpopo is derived from Rivombo (Livombo/Lebombo), a group of Tsonga settlers led by Hosi Rivombo who settled in the mountainous vicinity and named the area after their leader. The river is approximately long, with a drainage basin in size. The mean discharge measured over a year is per second at its mouth. The Limpopo is the second largest river in Africa that drains to the Indian Ocean, after the Zambezi River. The first European to sight the river was Vasco da Gama, who anchored off its mouth in 1498 and named it Espirito Santo River. Its lower course was explored by St Vincent Whitshed Erskine in 1868–69, and Captain J F Elton travelled down its middle course in 1870. The drainage area of Limpopo River has decreased over geological time. Up to Late Pliocene or Pleistocene times, the upper course of the Zambezi River drained into the Limpopo River. The change of the drainage divide is the result of epeirogenic movement that uplifted the surface north of present-day Limpopo River, diverting waters into Zambezi River. Course The river flows in a great arc, first zigzagging north and then north-east, then turning east and finally south-east. It serves as a border for about , separating South Africa to the southeast from Botswana to the northwest and Zimbabwe to the north. At the confluence of the Marico River and the Crocodile River, the name becomes the Limpopo River. There are several rapids as the river falls off Southern Africa's inland escarpment. The Notwane River is a major tributary of the Limpopo, rising on the edge of the Kalahari Desert in Botswana and flowing in a north-easterly direction. The main tributary of the Limpopo, the Olifants River (Elephant River), contributes around 1,233 million m3 of water per year. Other major tributaries include the Shashe River, Mzingwane River, Crocodile River, Mwenezi River and Luvuvhu River. In the north-eastern corner of South Africa the river borders the Kruger National Park. The port town of Xai-Xai, Mozambique, is on the river near the mouth. Below the Olifants, the river is navigable to the sea, though a sandbar prevents access by large ships except at high tide. Tributaries Basin characteristics The waters of the Limpopo flow sluggishly, with considerable silt content. Rudyard Kipling's characterization of the river as