The rest is saltwater. Longitudinal profiles are typically concave up in large rivers. Like a thermostat, a river tends to adjust toward a dynamic equilibrium. In terms of change of gradient, etc. Completed in 1970 with full hydropower generation from all 12 turbines.
Farmers now have to buy fertilizer.
Saltwater incursion into Nile Delta because not flushed out by seasonal floods. Public health problems from stagnant canals, etc. Flooded archaeological sites such as Abu Simbel. Led to decrease in fisheries in eastern Med. Mississippi River floods of 1993 .