The Orange river is the longest river in which country?

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.

At the western point of the Free State, southwest of Kimberley, the Orange meets with its main tributary, the Vaal River, which forms much of the northern border of the province. From here, the river flows further westward through the arid wilderness of the southern Kalahari region and Namaqualand in the Northern Cape province to meet with Namibia at 20°E longitude. From here, it flows westward for 550 km (340 mi), forming the international border between the province and Namibia's ǁKaras Region. On the border, the river passes the town of Vioolsdrif, the main border post between South Africa and Namibia.