Ohio River course forms the northern borders of West Virginia and Kentucky; and the southern borders of Ohio, Indiana and Illinois, until it joins the Mississippi River at the city of Cairo, Illinois. Where the Ohio joins the Mississippi is the lowest elevation in the state of Illinois, at . The Ohio River, which flows westward from Pittsburgh, Pennsylvania, to Cairo, Illinois, is the largest tributary, by volume, of the Mississippi River in the United States. At the confluence, the Ohio is considerably bigger than the Mississippi. Measured by long-term mean discharge in cubic feet per second and cubic meters per second,
Olifants River (Southern Cape) the east and flows westwards between the Swartberg and Kammanassie mountains to its confluence with the Gamka River. The southern slopes of the Swartberg Mountains are drained by the perennial Groot River, Kango River, Grobbelaars River, Wynands River, Kansa River and Vlei River tributaries, which flow into the Olifants River. The Kammanassie River rises in the Outeniqua and Kammanassie mountains near Uniondale and joins the Olifants River upstream of Oudtshoorn. Olifants River (Southern Cape) Olifants River () is a river in the Klein Karoo area of the Western Cape, South Africa. It has its origins in the Traka and Kalkwal