The Vaal River (pronounced and alternatively , especially by English speakers) 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 north of Ermelo and only about from the Indian Ocean. It then flows westwards to its conjunction with the Orange River southwest of Kimberley in the Northern Cape. It is long, and forms the border between Mpumalanga, Gauteng and North West Province on its north bank, and the Free State on its south.