an area of approximately 146 000 square kilometres, consisting of the Omo catchment in Ethiopia and the Turkwell and Kerio Basins in western Kenya. There is so far no evidence to show that during the Holocene and terminal Pleistocene the Nile catchment ever included the Chalbi Basin, an inland drainage basin whose centre is formed by the Chalbi playa, a surface of mud and salt subject to occasional flooding. However, recent research in this area has indicated that in the terminal Pliocene a body of water containing a Nilotic fauna existed as far east as Kargi, on the south-eastern margin of the Chalbi Basin. Near Kargi an outcrop of silt has yielded fossil bone, including remains of Lates niloticus, crocodile, turtle and hippopotamus. An age of about 2.3 millennia has been suggested for the fauna, while K-Ar dating of the lava overlying the bone beds yielded an age of 2.5 plus or minus 0.3 millennia. AT PRESENT, THE LIMIT of the Nile drainage basin south of the Sudan/Kenya border follows an approximately north-south alignment at less than 36 degrees East longitude; the Nile catchment does not include the Lake Turkana Basin (see Fig. la). It has long been recognized that during the Holocene, surface overflow between the Nile and Turkana drainage systems took place, and that at stages during the Pleistocene and Pliocene, there may have been connections between the ancestral Lake Turkana and the early Nile (Butzer, 1980; Harvey and Grove, 1982). In this paper, evidence is presented to show that the Nilotic drainage system may have extended as far east as Kargi (Longitude c. 37 degrees 35 minutes) during the terminal Pliocene. Modern conditions in the Turkana Basin and surrounding areas The area in question covers a large part of northern Kenya, together with parts of south-western Ethiopia and southern Sudan. Topographically it comprises parts of the eastern African plateau, interrupted by downfaulted and downwarped lowlands and by largely volcanic uplands. The climatic conditions of the area are predominantly arid to semi-arid, with some variation owing to relief and aspect. At present the regional drainage pattern is one of poorly integrated internal drainage basins, including the Lake Turkana Basin, the Suguta Valley, the Chew Bahir (Lake Stephanie) Basin and the Chalbi Basin.