The large-scale change from basin

The large-scale change from basin to perennial irrigation
began in modern times after 1800, with the building of bar-
rages. These low barriers across the Nile lifted water for move-
ment through canals to irrigate summer crops downstream.
Then, in 1902, a dam was built to actually store water for use in
the summer. This was the low dam placed at Aswan, in southern
Egypt. The final conversion to perennial irrigation came with
construction of the Aswan High Dam, completed in 1970.
Upstream from the Aswan High Dam, a reservoir called
Lake Nasser stretches 295 miles (475 kilometers) south to
Sudan. As it formed, this lake flooded a region known histori-
cally as Nubia. Except for some of the larger and more famous
structures that were relocated on higher ground, many ancient
Egyptian monuments were lost beneath the rising waters.
Nubians, the people who lived along the river, had to be relo-
cated to new settlements. Some of them have since returned to
the shores of Lake Nasser to fish and farm, although they must
often compete with crocodiles.