EPD 3 Prelims Practice Test

The main idea is that a large dam can create new health risks and trigger big environmental changes by altering water flow, sediment transport, and ecosystems. The Aswan High Dam led to four main adverse effects. First, malaria can spread more easily with irrigation and reservoir systems. Stagnant or slow-moving water in irrigation channels and surrounding areas provides ideal breeding grounds for mosquitoes, increasing malaria transmission. Second, schistosomiasis can rise as well. The slow, shallow waters created by dammed rivers and irrigation canals support the snail hosts that carry the parasite, elevating infection rates. Third, the dam disrupts sediment movement. With sediments trapped by the dam, downstream areas like riverbanks and the Nile Delta lose the material they would normally receive, making banks more vulnerable to erosion and accelerating delta retreat. Fourth, the ecosystem in the Mediterranean can suffer as Nile-derived nutrients and fresh water reach the sea less readily. This alteration in sediment and nutrient supply can harm marine life and fisheries in the coastal waters. All these factors together explain why this option lists the full range of adverse consequences. The other choices miss one or more of these interconnected impacts.