River, central Africa.
It is the chief southern tributary of the Congo River , measuring 1,338 mi (2,153 km) from its source in Angola to its confluence with the Congo. It runs east for its first 250 mi (400 km), then turns north to form the border between Angola and the Democratic Republic of the Congo (Zaire). It is unnavigable in the north, but water traffic is heavy from Kinshasa to Ilebo. After the Kasai is joined by the Kwango River, it is known as the Kwa.