The Orange River is the largest river of South Africa. It rises in the Drakensberg mountains along the border between South Africa and Lesotho, and runs westward along the southern boundary of the Free State area, and finally Atlantic Ocean at Alexander Bay , about equidistant between Walvis Bay and Cape Town.

The most notable tributary is the Vaal, which also rises in the Drakensberg east of Johannesburg and forms the boundary between Transvaal and the Free State before joining the Orange southwest of Kimberley.