Maybe a “little bit” wrong at most. Nile valley farmers have irrigated from time immemorial. Among some of the ancient ruins, thousands of years old, are huge reservoirs where flood waters were captured for irrigation when it turned dry, as it inevitably does there. Extensive canals along the banks carry water a long way from the river, and from which farmers irrigate. Yes, the annual floods deposited rich silt and watered the land it reached, but you can’t plant during a flood, and any farmer will tell you that land dries out very quickly in hot, dry air when the water (name removed by moderator)ut stops. Without irrigation, the Nile valley would be nothing but a river with a narrow strip of swamps alongside, and would never have been.
Farmers in Egypt irrigate and farm essentially the same land they always irrigated and farmed, with the addition of a lot of newly irrigated land along Lake Nasser. Otherwise, what has changed due to the Aswan high dame are two things: First, the controlled flooding does not now deposit the layer of silt the uncontrolled floods once did; something that now requires more fertilizer and will also contribute to the eventual silting-up of Lake Nasser. Second, the lack of flooding has increased the population of schistosomiasis-carrying snails in the Nile and irrigation canals, which is most definitely not a good thing.
The Aswan high dam(or any other dam) may be critiqued on its own merits, but it is not what brought riverside irrigation to the Nile valley thousands of years ago.