An Estuarine Fauna in a Freshwater Lake in South Africa

Abstract

AN expedition from the Department of Zoology and Entomology, Rhodes University, recently visited Lake Sibayi in Northern Zululand, Natal. The lake is completely separated from the sea by a line of forest-covered sand-dune which is 600 ft. high at the highest point. During July the lake water was homogeneous throughout, thus there was no stratification with regard to temperature (17°–18° C) or chlorides. The chloride content of the water in July, which is the dry season, was 135 p.p.m. This is high, and the lake can be regarded as being chloride-enriched. The source of chloride is possibly the cyclical salt carried in the air from the sea and precipitated in the basin, the sea being only half a mile from the lake at its nearest point. However, assuming that the chloride is derived from the sea and that the salts present in the lake are in the same proportion as in sea-water, the salinity would be in the region of 0.25 parts per thousand. This is extremely low and the lake must perforce be regarded as a freshwater environment.