The Nile flows through Cairo before emptying into the Mediterranean Sea. It is traditionally regarded as the world’s longest river, running about 6,650 kilometres through northeastern Africa, although river-length comparisons depend on how sources and tributaries are measured.
The Nile has two major tributaries: the White Nile, whose farthest headwaters are associated with the Great Lakes region of East Africa, and the Blue Nile, which rises in Ethiopia. They meet at Khartoum in Sudan. The Blue Nile carries much of the river’s sediment and seasonal flow, while the White Nile provides a steadier contribution.
Ancient Egyptian civilization depended on the river’s predictable flooding, which deposited fertile silt across the valley and delta. The Aswan High Dam, completed in the 1970s, greatly reduced natural flooding and created Lake Nasser, while providing electricity and water control. Cairo stands near the point where the river divides into branches across the Nile Delta.