Every year, the Nile floods in the summer. These floods brought nutrients and mineral that made the soil around the Nile so fertile-so ideal for farming. If it was a high-water year, the whole crop may be entirely wiped out, however. These floods were so very unpredictable that it was considered necessary to build a dam to control them..
The Nile is subject to an annual summer flood as waters from Ethiopia flow down the river. The banks of the river have been used in agriculture since antiquity and rely on the flood to provide and maintain fertility. As the population along the river grew there came the need to control the flood waters to protect farmland and cotton fields. The British began construction of the first dam in 1899 and it was completed in 1902. A gravity dam, it was 1,900 m long and 54 m high. The initial design was soon found to be inadequate and the height of the dam was raised in two phases, 1907-1912 and 1929-1933.
Construction began in 1960. The High Dam, El Saad al Aali, was completed on July 21, 1970 with the first stage finished in 1964. The reservoir began filling in 1964 while the dam was still under construction and first reached capacity in 1976. The reservoir raised concerns from archaeologists and a rescue operation was begun in 1960 under UNESCO. Sites were surveyed and excavated and 24 major monuments were moved. See Abu Simbel.
In addition to the benefits, however, damming the Nile caused a number of environmental issues. The silt which made the Nile region fertile is instead held at the dam, leading to (expected) silting of the reservoir, which will eventually render Lake Nasser useless for water storage volume. There is some erosion of farmland down-river. Erosion of coastline barriers, due to lack of new sediments from floods, will eventually cause loss of the brackish water lake fishery that is currently the largest source of fish for Egypt, and the subsidence of the Nile Delta will lead to inundation of northern portion of the Delta with seawater, in areas which are now used for rice crops. The need to use artificial fertilizers supplied by international corporations is controversial too. Indifferent irrigation control has also caused some farmland to be damaged by waterlogging and increased salinity, a problem complicated by the reduced flow of the river, which allows salt water further into the delta. Mediterranean fish stocks are also impacted by the dam. The eastern basin of the Mediterranean is low in fertility, and traditionally the marine ecosystem dependended on the rich flow of phosphate and silicates from the Nile outflow. Mediterranean catches decreased by almost half after the dam was constructed, but appear to be recovering. A new fishing industry has been created around Lake Nasser. The dam has been implicated in a rise in cases of schistosomiasis and (bilharzia).