There are few natural lakes in South Africa. We depend on rivers, dams and underground water for our water supply. Flowing from east to west is the largest river in the country, the Orange River, which drains most of the rest of the country. Its water comes from sources in the Drakensberg and Maluti Mountains, and it flows into the Atlantic ocean on the West coast. About half of South Africa's annual rainfall is stored in dams.
Dams have both positive and negative ecological impacts.
They can be beneficial in that they regulate the flow of a river, reducing flood damage, and contributing to a perrenial rather than seasonal flow. In addition, sediment is deposited in a dam, and the growth of aquatic plants means that excess nutrients are removed from the water. Thus water leaving a dam might be cleaner than water entering it. Negative ecological impacts include a reduction in strong water flow which reduces the river's scouring ability. This, in turn, can lead to silting of estuaries.