The Vaal River is the largest tributary of the Orange River in South Africa. The river has its source near Breyten in Mpumalanga province, east of Johannesburg and about 30 kilometres (19 mi) north of Ermelo and only about 240 kilometres (150 mi) from the Indian Ocean. It then flows westwards to its confluence with the Orange River southwest of Kimberley in the Northern Cape. It is 1,458 kilometres (906 mi) long, and forms the border between Mpumalanga, Gauteng and North West Province on its north bank, and the Free State on its south.

The Orange River 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. Other names include simply the word for river, in Khoekhoegowab orthography written as !Garib, which is rendered in Afrikaans as Gariep River with the intrusion of a velar fricative in place of the alveolar click, Groote River or Senqu River, derived from ǂNū "Black". It is known in isiZulu as isAngqu.