The Kasai River (called Cassai in Angola) is a tributary (left side) of the Congo River, located in Central Africa. The river begins in central Angola and flows to the east until it reaches the border between Angola and the Democratic Republic of the Congo (DRC), where it turns north and serves as the border until it flows into the DRC. From Ilebo, between the confluences with Lulua river and Sankuru river, the Kasai river turns to a westerly direction. The lower stretch of the river from the confluence with Fimi river, is known as the Kwa(h) River, before it joins the Congo at Kwamouth northeast of Kinshasa. The Kasai basin consists mainly of equatorial rainforest areas, which provide an agricultural land in a region noted for its infertile, sandy soil. It is a tributary of Congo river an