evidence: The Orange River is the longest river in South Africa. It flows 1,300 miles (2,100 kilometers) across the width of the country. The river forms a large part of the border between South Africa and Namibia. [...] The Orange River flows from east to west across South Africa. It flows through the Eastern Cape, Free State, and Northern Cape provinces. The river flows into the Atlantic Ocean at Alexander Bay in the Northern Cape. The Vaal and Caledon rivers are two main tributaries of the Orange River. The Orange River plays an important role in the economies of both Lesotho and South Africa. The river provides fresh water for crop irrigation and drinking. The Orange River is also used to generate power.