The Great Kei River is a river in South Africa in the Eastern Cape province. Before it becomes the Great Kei, the Swart-Kei River (Black Kei River) and the Wit-Kei River (White Kei River) join forces, northeast of Cathcart. It flows for 520 km[1] and ends at the Indian Ocean with the small town Kei Mouth on the west bank. The river serves as the southwestern border of the Transkei region.