East African Rift Valley Lakes, GIWA Regional assessment 47.

Abstract

The East African Rift Valley Lakes (EARVL), GIWA region 47, runs from the northern end of Lake Turkana Basin to the southern tip of the Lake Malawi/Nyasa Basin and includes all the natural habitat and associated human communities found within the Rift Valley and on the adjacent escarpments (Figure 1). It encompasses parts of the following countries; Ethiopia, Kenya, Sudan, Uganda, Tanzania, Rwanda, Burundi, Democratic Republic of Congo (DR Congo), Zambia, Malawi and Mozambique. The main lakes include Victoria, Tanganyika, Malawi, Turkana, Albert, Edward, George and Kivu. All are tropical and together comprise the African Great Lakes ecoregion. However, each lake lies within its own separate drainage basin, with its own assemblage of endemic organisms, most notably the cichlid fi sh species-fl ocks. Each lake diff ers substantially with respect to limnology, catchment dynamics and human impacts (Hamilton 1982). For the purpose of GIWA assessment, the following lakes that are characteristic of most of the transboundary water bodies in the region were selected for the exercise: Lake Turkana, Lake Victoria, Lake Tanganyika and Lake Malawi. These are the largest of the East African Rift Valley lakes and are among the oldest lakes in the world. All these lakes are extremely sensitive to climate change. Lake Turkana, the largest closed-basin lake is up to 115 m deep, moderately saline and alkaline, and lies in a topographically closed basin located in the arid northwestern part of Kenya, though the delta of the Omo River, the principal affluent, lies within southwestern Ethiopia. Lake Victoria is, by area, the second largest lake in the world and the largest in Africa, though relatively shallow, with a maximum depth of 80-90 m. More than 80% of its water input is derived directly from rainfall on the lake surface, and about 7% fl ows from the western side of the basin through the Kagera River. It is drained by the Nile River from Owen Falls on its northern rim. Lake Tanganyika is the longest lake in the world (673 km) though only 12–90 km wide. Its average depth is 570 m, with a maximum depth of 1 470 m, making it the world’s second deepest lake. The lake drains westwards through the Lukuga River into the basin of the Congo River. Lake Malawi is long and narrow, the fourth deepest inland water body in the world (700 m) and the world’s fourth largest body of freshwater. It drains southwards via the Shire River to the Zambezi Basin.