The second dam (or the High Dam) was built in 1970 with Soviet assistance and cost $1 billion. The material used to create this dam occupies 18 times the volume of the Great Pyramid! The length of the dam is almost 4 km and its base is close to 1000 m wide. With 12 generators inside the dam, it can generate 2.1 gigawatts/hour when operating at peak capacity. Currently, only a tiny fraction of this power is used, but the government is trying to start exporting the electricity to Europe or Turkey.
It is almost impossible to fully appreciate the size of the High Dam just by driving across the top of it. While we were standing on the top enjoying the view, the guards kept hovering around insisting "Don't zoom!" "Not allowed to zoom!" They were no doubt afraid that we were stealing the plans for the parts of the generators and power plant apparatus that were visible from where we were. It turns out that the dam is a very high risk target for terrorism. The dam as a whole could withstand a nuclear blast without breaking. A well placed bomb inside the dam, however, would release the 5.97 trillion cubic feet of water stored in Lake Nasser. The result would be an enormous tidal wave that would sweep down the valley to Cairo in less than 7 hours. Imagine trying to evacuate 17 million people from a capital city in less than 7 hours and you can understand their concern.
As a result of the construction of these two dams, 13 ancient Greek and Egyptian temples were drowned in the resulting lake. They have all been relocated with the assistance of a number of other countries. Unfortunately, many of them have significant water damage from being submerged for a long time. While the increased control of the Nile has greatly extended the growing season and made it possible to irrigate a much larger part of the country, overall fertility of the Nile valley has decreased. The annual Nile floods used to bring in a lot of nutrient rich silt which is now lost. The reduced flow out of the Nile delta is also allowing salt from the Mediterranean to seep back into the Delta reducing fertility further there.