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Figure 8. Sewage alone . . .Click to Enlarge Image

Fish caught in Mediterranean waters just off the Nile River Delta have been an important source of protein for Egyptians for millennia, despite the general lifelessness of the eastern Mediterranean. Each summer before 1964, rains in Ethiopia produced a rush of water down the Nile that carried vital nutrients to feed the fishery. But when the Aswan High Dam closed its gate in 1964, the nutrient flow was blocked, and catches soon plummeted. Mysteriously, however, fishing began to pick up again around 1980 and now exceeds pre-dam levels. The author proposes that nutrient flow has been restored by human activities, including the use of fertilizers for agriculture and the development of sewage systems used by a burgeoning population.

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