There is a conflict between Egypt and Ethiopia, because the latter wants to build a dam on the Nile river. Citing this article:
[Egypt] fears the Nile dam will reduce its share of the river and leave the country with dwindling options as it seeks to protect its main source of fresh water.
What do they mean by "reduce its share of the river"? As far as I understand, the dam will create a reservoir, which will initially divert some water to be filled, but once that is done, the flow of the river should be the same. Is Egypt worried about this initial reduction, or do dams somehow reduce the flow of a river?
If so, what is the mechanism? I would guess that this is due to increased evaporation from the river, since the reservoir has a bigger surface than the usual river, but then again, it also collects more rain.