Cahora Bassa, a new impoundment in the middle Zambezi River, was closed in December 1974, filling rapidly to 12 m below full supply by May 1975. The principal objective of the construction is the production of 3,870 MW of electricity, making Cahora Bassa the largest power-producing barrage in Africa.

The lake, with five basins, lies along a west-east axis almost parallel to prevailing southeasterly winds. Limnological records, from several stations along the lake axis, indicated homoisothermal conditions until September, the hot day season. From then until records ceased in December, thermocline and oxyclines were present in the deeper eastern basins. Hydrogen sulphide was recorded in hypolimnial waters towards the end of the year. Open water of the shallow, wind- and wave-swept eastern basins remained oxygenated throughout the year.

Water transparency increased five-fold from April to December, increasing too from east to west. pH was alkaline becoming more acid in cool winter months and in bottom waters of stratified basins. Conductivity ranged from 95 to 119 μS cm^-1 with higher values in shallow lake margins. Chemical content of surface waters showed little seasonal or spatial variation and was, in general, comparable with pre-impoundment levels.

Duration of the initial 'productive phase' will probably be shorter than Kariba due to more rapid lake water exchange but indications are that productivity will be higher in the maturation phase (1, 5).