Why there's an argument over Africa's largest hydroelectric dam

The Grand Ethiopian Renaissance Dam (GERD) is one of Africa's biggest engineering projects.

Dams are built across a river to stop or control the flow of water, but not everyone agrees with how this one should be used.

Built on a tributary of the river Nile, the dam will use the flow of water to produce electricity for millions of Ethiopians, with around half of the country's population still without access to power.

But Egypt, a country that depends on the Nile for nearly all its of its fresh water, is worried the dam might reduce its supply, especially during dry years.

Ethiopia says the dam won't cause harm and that it's using the river fairly to help its people.