evidence: The Orange River (from Afrikaans/Dutch: Oranjerivier) is a river in Southern Africa. It is the longest river in South Africa. With a total length of 2,432 km (1,511 mi), the Orange River Basin extends from Lesotho into South Africa and Namibia to the north. It rises in the Drakensberg mountains in Lesotho, flowing westwards through South Africa to the Atlantic Ocean. The river forms part of the international borders between South Africa and Lesotho and between South Africa and Namibia, as well as several provincial borders within South Africa. Except for Upington, it does not pass through any major cities. The Orange River plays an important role in the South African economy by providing water for irrigation and hydroelectric power. The river was named the Orange River in honour of the Dutch ruling family, the House of Orange, by the Dutch explorer Robert Jacob Gordon. [...] The Orange River then runs westward through South Africa, forming the south-western boundary of the Free State province. In this section, the river flows first into the Gariep Dam and later into the Vanderkloof Dam. From the border of Lesotho to below the Vanderkloof Dam, the river bed is deeply incised. Further downstream, the land is flatter, and the river is used extensively for irrigation.