The Nile delta, or Lower Egypt, covers an area of 9,650 square miles (25,000 sq km). It is about 100 miles (160 km) long from Cairo to the Mediterranean, with a coastline stretching some 150 miles (240 km) from Alexandria to Port Said. As many as seven branches of the river once flowed through the delta, but its waters are now concentrated in two, the Damietta Branch to the east and the Rosetta Branch to the west. Though totally flat apart from an occasional mound projecting through the alluvium, the delta is far from featureless; it is crisscrossed by a maze of canals and drainage channels. Much of the delta coast is taken up by the brackish lagoons of lakes Mary??, Idk?, Burullus, and Manzilah. The conversion of the delta to perennial irrigation has made possible the raising of two or three crops a year, instead of one, over more than half of its total area.
The cultivated portion of the Nile valley between Cairo and Asw?n varies from 5 to 10 miles (8 to 16 km) in width, although there are places where it narrows to a few hundred yards and others where it broadens to 14 miles (23 km). Since the completion of the Aswan High Dam in 1970, the 3,900-square mile (10,100 square km) valley has been under perennial irrigation.
Until it was flooded by the waters impounded behind the High Dam to form Lake Nasser, the Nubian valley of the Nile extended for 160 miles (250 km) between the town of Asw?n and the Sudanese border—a narrow and picturesque gorge with a limited cultivable area. The 100,000 or so inhabitants were resettled, mainly in the government-built villages of New Nubia, at Kawm Umb? (Kom Ombo), north of Asw?n. Lake Nasser was developed during the 1970s for its fishing and as a tourist area, and settlements have grown up around it.