The Vaal Dam in South Africa was constructed in 1938 and lies 77 km south of OR Tambo International Airport. The lake behind the dam wall has a surface area of about 320 square kilometres (120 sq mi) and is 47 meters deep. The Vaal Dam lies on the Vaal River, which is one of South Africa's strongest-flowing rivers. Other rivers flowing into the dam are the Wilge River, Klip River, Molspruit and Grootspruit.