From Envirowiki

Before the Aswan dam the Nile river flooded regularly, damaging cities and endangering lives. the flood was also the only irrigation for farmers on the floodplains, and s it only happened for a month or so every year, the land was dry for the rest of the year and practically barren, for farming purposes.

[edit] 1 The Idea

Assumably with the best intentions the British Government of the day (turn of last century) decided that lower Egypt needed:

• Flood mitigation
• Hydro-electricity, and
• year-round irrigation

Obviously these would be great things to have (might take some of the excitement out of life, though). The values are commendable: food security, safety, and the possibility to grow economically. But that’s not exactly what happened.

[edit] 2 The Fuck-up

all the benefits of the dam materialised perfectly as expected. the Nile now has no dangerous floods, heaps of hydro-power, and year-round irrigation-on-demand. Unfortunately, it also has:

• Less soil nutrients: the floods brought nutrient rich soils from the upper Nile. Now Egyptians have to BUY fertiliser.
• less biodiversity: the fish in the Nile delta, which supported a lot of people, lived off (down the food chain) sea grass, which lived off the nutrients of the flood-silt. Fish stocks dropped by about 2/3.
• Dredging is now required to remove the silt from behind the dam.
• Schistosomiasis, a parasite that lives in the flood-plain mud now has a year-round water supply due to irrigation. It is horribly debilitating and incurable. Infection rates jumped from 5% to 40%.