The inflow of the Rusizi River to Lake Tanganyika

The inflow of River Rusizi to Lake Tanganyika has been assumed not to mix w ith the lake epilimnion as it would sink as an interflow or an underflow, b ecause of its higher density due to sediment load, lower temperature and hi gher salinity. Nevertheless, efforts made to trace the Rusizi flow into the lake have failed. Ten sampling surveys were carried out from March 1994 to July 1995. Each consisted of 22 samples, at different distances off the Ru sizi estuary and at different depths. Eighteen physical and chemical variab les were studied at each site. The Rusizi water was always denser (800 - 14 00 g m(-3)) than the lake water. The relative importance of temperature, su spended solids and salinity varied seasonally. A descent of the Rusizi infl ow was observed. Close to the river estuary, river and lake waters mixed an d Rusizi sediments settled. Complete mixing occurred within 800 m offshore. The Rusizi inflow merged with the epilimnion rather than the hypolimnion. Horizontal spread by shorebound currents seemed to be more important than o ffshore spread.