Ethiopia on Tuesday officially inaugurated the Grand Ethiopian Renaissance Dam (GERD), Africa’s largest hydroelectric project, in a move hailed by Addis Ababa as a milestone for development but viewed with concern by downstream nations Egypt and Sudan.

The $5 billion dam, located on a tributary of the River Nile in Guba, has reached its full generation capacity of 5,150 megawatts, placing it among the 20 biggest hydroelectric dams in the world. Its construction, which began in 2011, is central to Ethiopia’s economic ambitions, with promises to expand electricity access for its more than 120 million people and export surplus power to neighbouring countries.

At the inauguration ceremony, Prime Minister Abiy Ahmed addressed dignitaries, including the presidents of Somalia, Djibouti and Kenya, under the canopy of a massive Ethiopian flag. Fighter jets flew low over the mist as water cascaded 170 meters from the dam’s wall.

“To our (Sudanese and Egyptian) brothers; Ethiopia built the dam to prosper, to electrify the entire region and to change the history of black people,” Abiy said. “It is absolutely not to harm its brothers.”

The dam’s vast reservoir, larger than Greater London, has already altered landscapes and, according to Ethiopian officials, will stabilize water supplies for irrigation while reducing floods and drought downstream.

However, Egypt and Sudan remain deeply uneasy. Egypt, which relies on the Nile for about 90 percent of its fresh water, fears the dam could restrict its supply during droughts. Cairo argues the project undermines colonial-era water treaties and poses an existential threat to its 108 million people.

Egyptian Foreign Ministry spokesperson Tamim Khallaf said on Monday that Cairo would “exercise its right to take all the appropriate measures to defend and protect the interests of the Egyptian people,” while continuing to monitor developments on the Blue Nile.

Sudan has echoed Egypt’s call for a legally binding agreement on how the dam is filled and operated, though it also stands to benefit from regulated flooding and access to cheaper electricity.

Despite years of negotiations, a comprehensive deal has yet to be reached, leaving the GERD as both a triumph of Ethiopian ambition and a flashpoint of regional tension.