The Nile River flows through the African desert. Thin strips of rich, green land stretch out around it. Wherever the river goes, people have always gone too, building homes and planting good food beside the water. The country of Egypt would never have existed without this famous river. People still make their homes in this ancient land of pyramids and mummies. And they still need the Nile for life. What would happen if its mighty waters stopped flowing?

Egyptians may soon find out. They share the river with their Ethiopian neighbors. Right now Ethiopians are busy building a dam on the Nile. The Grand Renaissance Dam stands more than 500 feet tall—the biggest one in Africa. Ethiopians will use the moving water to make electric power. That will fill a huge need. Three out of every four Ethiopians do not have electricity. The dam’s power seems like a dream come true to them. They think, “Look at our dam! It proves our country has power in the world.” Schoolchildren even sing songs about the dam. They chant, “This is our destiny!” But the dam may also cause less Nile water to flow to Egypt. It’s great that Ethiopians will get to switch on lights. But what if Egyptians can’t turn on their tap water anymore?

Can Egyptians and Ethiopians all get what they need so badly? Maybe. Once they finish the dam, Ethiopians will fill the dam’s reservoir. (A reservoir stores water that will run through turbines to make electric power.) If they fill it quickly, Egypt will lose a lot of water right away. Meanwhile, Ethiopia will light up with electricity much sooner. But Ethiopia could also fill the reservoir slowly. If it does, Egypt will suffer much less as more of the Nile’s water continues to flow downstream. But Ethiopia will also get less electricity more slowly.

You can see why the two countries are more than a little upset with each other. “It won’t cause that much trouble for Egypt,” Ethiopian officials reason. Egyptians answer, “That’s easy for you to say!”