It will definatly affect Egypt’s Nile area in profound ways.
The benefits to Ethiopia regarding the dam are huge. From their perspective not filling the dam, which has taken ten years to build, would be criminal. More than half the country has little water and no electricity. Filling the dam is essential to survival. I fully expect their neighbors to destroy the dam.
Before taking a stand, bear in mind the Rio Grand is usually a bunch of disconnected puddles when it reaches the Mexican border.
Egypt going to have to act