Bump. I have wondered the same thing
The only thing that could happen to that damn or Egypt to make it inhabitable for 40 years including by fish or animals is radioactive waters, maybe when the damn is hit be a nuclear tipped rocket and all the back waters now radioactive, wash over the Egyptian land and contaminate it for "40" years?
..."Thus, this location is identical to the modern place name Aswan, now the site of a huge dam. Using Russian technology, the Egyptians completed the dam, effectively placing themselves in the position of being able to say, The river is mine, and I have made it."
http://www.prophecyinthenews.com/egypt-aswan-and-the-coming-flood/