Ethiopia seeks to transform itself into a middle-income country, and so it needs electricity. Africa's largest hydroelectric power station and one of the world's largest dams will do that, but with 85% of the river emerging from the Ethiopian highlands, Egypt is concerned its rival has the capability to control the flow of the river.
Sudan certainly welcomes it. The Grand Ethiopian Renaissance Dam is just a few kilometres from the border and the pylons are already in place, waiting for the power generation to begin and for cheap, renewable power to fizz through the cables. At the moment the difference between high water and low water level in Sudan is 8m, and that makes its vast irrigation projects harder to manage. With the dam in place, the difference will be 2m and the flow of the river will come year-round.
"For Sudan it's wonderful," says Osama Daoud Abdellatif, the owner of the Dal Group which runs farms and irrigation projects. "It's the best thing that's happened for a long time and I think the combination of energy and regular water levels is a great blessing."
"It's very much a game changer, a new order is beginning in the whole region now," believes Rawia Tawfik, an Egyptian academic working in Germany. "Ethiopia for the first time is combining both the physical power of being an upstream country that can in one way or another control the River Nile's flow, and the economic power of being able to construct a dam depending on its own domestic resources."
Egypt's minister of water resources and irrigation, Mohamed Abdel Aty, is extremely angry. Hydroelectric power stations do not consume water, but the speed with which Ethiopia fills up the dam will affect the flow downstream. It will take time to fill up a reservoir which is going to be bigger than Greater London and will flood the Nile for 250km (155 miles) upstream.
"We are responsible for a nation of about 100 million", he says. "If the water that's coming to Egypt reduced by 2% we would lose about 200,000 acres of land. One acre at least makes one family survive. A family in Egypt is average family size about five persons. So this means about one million will be jobless. It is an international security issue."
The dam is impressive. After five years it is two-thirds finished - and it already crosses the river. There is nothing Egypt can do about it, except take military action which would be extreme. That is why diplomacy and collaboration are the only means of resolving this issue when issues like nationalism and the relative strength and importance of countries is concerned.