The topography of Egypt is dominated by the Nile. For about 750 miles of its northward course through the country, the river cuts its way through bare desert, its narrow valley a sharply delineated strip of green, abundantly fecund in contrast to the desolation that surrounds it. From Lake Nasser, the river's entrance into southern Egypt, to Cairo in the north, the Nile is hemmed into its trenchlike valley by bordering cliffs, but at Cairo these disappear, and the river begins to fan out into its delta. 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.