LAKES OF THE NORTH EASTERN REGION OF THE OKAVANGO SWAMPS, BOTSWANA

The Okavango Swamps of nothern Botswana are situated in the proximal r eaches of a large alluvial fan (20000 km2), the terminal depository of the Okavango River. The river divides into a number of distributaries at the head of the fan, which sustain 6000 km2 of permanent swamp. La kes form an important morphological and ecological feature of this swa mp. The lakes are associated with a meander belt, but this belt is 200 0 to 3000 years old and is not related to the present distributary cha nnel system. The lakes have arisen from reflooding of old oxbows, or d amming of water against the old meander ridge. Fifty years of aerial p hotographic record indicate that some lakes have been stable while oth ers have disappeared. Avulsion occasionally diverts a channel into a l ake by way of a hippopotamus trail, initiating a vegetation succession al sequence which rapidly leads to closure of the lake by vegetation. It is replaced by a channel, flanked by densely vegetated swamp. Lakes not connected to channels fill very slowly by the accumulation of aut ochthonous organic material.