The Vaal Dam in South Africa was constructed in 1938 and lies 77 km south of OR Tambo International Airport, Johannesburg. 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, Molspruit and Grootspruit. It has over 800 kilometres (500 mi) of shoreline and is South Africa's second biggest dam by area and the fourth largest by volume.

The Vaal River is the largest tributary of the Orange River in South Africa. The river has its source near Breyten in Mpumalanga province, east of Johannesburg and about 30 kilometres (19 mi) north of Ermelo and only about 240 kilometres (150 mi) from the Indian Ocean. It then flows westwards to its confluence with the Orange River southwest of Kimberley in the Northern Cape. It is 1,458 kilometres (906 mi) long, and forms the border between Mpumalanga, Gauteng and North West Province on its north bank, and the Free State on its south.