...In the case of the Aswan High Dam, nearly all negative impacts have come to pass, even since the onset of construction, with up to 100,000 Sudanese permanently displaced by the reservoir. The rich silt that used to fertilize the dry desert lands adjacent to the Nile during annual floods is now sitting at the bottom of Lake Nasser. Consequently thousands of farmers have been compelled to use artificial fertilizers and pesticides, which is having further devastating effects on the once pristine floodplain. The once rich soil laden annually with the Nile’s great gift – the silt – has now become substandard and in many areas is rated as poor quality land. About 95 percent of Egypt’s people live within 12 miles of the Nile River, with many working as farmers. All are be affected by the changes wrought by the Aswan High Dam.
Other current environmental issues related to the Aswan High Dam are agricultural land being lost to urbanization and windblown sands; increasing soil salination below the Dam, desertification, oil pollution threatening the coral reefs, beaches and marine habitats; and increasing water pollution from the use of artificial, imported pesticides. The Mediterranean, without the rich nutrients coming from the Nile waters, has become a poverty-stricken, nutrient-depleted water basin since the construction of the Aswan Dam. For thousands of years the snow waters have come down and poured themselves into the Nile, carrying with them the dead and decaying plants, small pebbles and silt. This muddy water is the silt. This silt was the most precious gift of the Nile, as during the annual floods it got deposited all over the land, creating rich soil leading to bountiful crops for the people. Where is this silt today? It is trapped in the man-made reservoir called Lake Nasser.
With the building of the Aswan High Dam, much of Lower Nubia became submerged under the reservoir. Ancient monuments and archaeological sites were buried forever despite various rescue operations. Only 20 monuments from the Egyptian part of Nubia and four from the Sudan were rescued, dismantled and re-erected on higher ground near Lake Nasser.
Still another side effect of the Aswan High Dam is an increase of the parasitic disease schistosomiasis (bilharzias), associated with the stagnant water of the fields and due to the thick plant life that has grown up in Lake Nasser, which hosts the snails that carry the disease. Infection with schistosomiasis occurs when the skin comes in contact with contaminated fresh water in which certain types of snails that carry schistosomes are living. Schistosoma parasites can penetrate the skin of persons who are wading, swimming, bathing or washing in the contaminated water, such as in Lake Nasser. Within a few weeks, worms grow inside the blood vessels of the body and produce eggs. Symptoms are rash, fever, chills, cough, muscle aches, and later possible seizures, paralysis or spinal cord inflammation. If repeatedly infected the parasite can damage the liver, intestines, lungs and bladder.
The silt that is accumulating unutilized in Lake Nasser, trapped by the dam, will eventually – in a few hundred years – render Lake Nasser useless for water storage. Because of no silt, there is now too much erosion of farmland downstream from the dam. The Nile Delta, once rich in nutrients from the silt of the Nile, has lost much of its fertility. The red-brick construction industry which used delta mud has also been affected by the poor quality of the mud in recent years.<16> There is substantial erosion of coastlines all along the eastern Mediterranean due to lack of sand once brought down by the Nile. The use of artificial fertilizers has caused chemical pollution of the water, whereas the traditional silt had only good impact on the environment. Certain areas of farmland have incurred waterlogging. In addition, due the lower levels of delta water, salt water is coming into the land more and is destroying the rice crops along the delta. The eastern basin of the Mediterranean, now far less fertile than before the dam, has impacted the fisheries because the marine ecosystem had always depended upon the rich flow of phosphate and silicates from the Nile waters. The Nile Delta is becoming smaller each year because it no longer receives sediment and pebbles from the river. The pebbles and sediment are stuck behind the dam. Hence much wildlife is losing its home because the delta is shrinking in size...
Other than that, the dam has been a huge success.
http://www.proutworld.org/features/nile.htm