Molopo River, river in Southern Africa. It rises east of Mahikeng ( Mafikeng, Mafeking) in North West province, South Africa, and flows generally west for about 600 miles (1,000 km) to join the Orange River near the southeastern border of Namibia. Intermittent and usually dry, the Molopo also marks part of the southern boundary between Botswana and South Africa. In its lower course the river passes through the Kalahari basin.