The Senegal River is a major river in West Africa, running through Senegal, Mauritania, Mali, and Guinea. It is the longest river in West Africa, with a length of 1, 020 miles. The Vaal River is a tributary of the Orange River in South Africa. It is approximately 644 miles long and is the main source of water for Gauteng Province, the country's most populous province. Both the Senegal and Vaal Rivers are important sources of water for South Africa.