Which natural freshwater lake is South Africa's largest?

South Africa’s largest natural freshwater lake is Lake Sibaya.

Lake Sibaya lies in KwaZulu-Natal on South Africa’s northeastern coastal plain. Published measurements vary with the survey and definition, but its area is commonly reported in the range of roughly 64 to 77.5 square kilometres, enough to make it the country’s largest natural freshwater lake.

The lake is separated from the Indian Ocean by a forested coastal-dune barrier, with dunes rising to about 165 metres. It has no direct river outlet and is sustained mainly by local runoff and groundwater, giving it a distinctive coastal-lake setting.

Lake Sibaya is part of the iSimangaliso region and has been a Ramsar Wetland of International Importance since 28 June 1991. Lake St Lucia is larger, but it is an estuarine lake system whose salinity can range from nearly fresh to hypersaline, so it is not the answer to this freshwater question.