The Okavango River Basin extends across three countries: Angola, Namibia and Botswana, covering an area of some 700 000 km². Yet, the section that contributes actively to surface flows, that is the hydrologically active part of the basin only covers an area of about 192,500 km² (Mendlesohn and El Obied 2004). In Angola the river is called the Rio Cubango, flows southwards in a series of parallel tributaries and falls mainly within the Kuando Kubango Province. The main tributary is the Rio Cuito. In Namibia, the Okavango River is often referred to as the Kavango River, it flows eastwards through the Kavango Region for some 415 km before tuming abruptly southwards at Mukwe from where it forms the border with the Caprivi Region for the next 55km, until it enters Botswana at Mohembo (Bethune 1991). In Botswana, it forms the world famous Okavango Delta in Ngamiland. The Okavango Delta covers 22 000 km² and can be divided into four main regions, the panhandle, the permanent swamp in the upper section of the alluvial fan, the seasonal swamps in the lower section of the alluvial fan and several large islands such as Chief's Island and the sandveld peninsulas that extend from the mainland into the delta as found in the eastern part of the Moremi Wildlife Reserve (Ellery and Ellery 1997). The altitude varies from over 1500mm above sea level at the source, to 1000m for most of the Namibian section to 940 m ASL at Maun.