Many of these artificial lakes were created in the SMR during the mid to latter part of the twentieth century to store water for a variety of purposes. Perhaps the most famous is Lake Nasser and the Aswan High Dam constructed in the 1960s. This large dam not only regulates the seasonal Nile floods but also enables hydroelectric power generation. Also, the function of most North African dams and reservoirs is to provide water for irrigation and for drinking water supply. They extend over large areas and exceed the size of natural lakes in both the Maghreb region and in Egypt. Being dependant on rainfall far away in Ethiopia and Central Africa, Lake Nasser is replenished annually by high Nile flow in late summer. In the western SMR, however, reservoir water levels are strongly controlled by local precipitation and water demand, but they typically rise in winter as a result of silt laden water inflows and fall strongly in summer. Depressions around their margins can, however, preserve water all the year and constitute permanent marshy zones. Hence, while the littoral shore of these reservoirs are largely devoid of life, especially aquatic plants, these wet marginal depressions can support considerable diversity and often with abundant hydrophyte communities. All these artificial water bodies face problems of high siltation through erosion of newly established shorelines and delivery of silt inflowing water.
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