Egypt, Ethiopia, and Sudan are engaged in last-ditch talks to resolve a dispute over Addis Ababa’s construction of a giant dam on the river Nile that Cairo fears could lead to damaging water shortages. This month Ethiopia is set to start storing water in the vast reservoir of the $4.8bn Grand Ethiopian Renaissance Dam, set to be Africa’s largest, and which it sees as a pathway to widespread electrification and a prosperous future.

But after almost 10 years of failed talks with Egypt and Sudan, the two countries with which it shares the Blue Nile, tensions are rising and mistrust prevails. Addis Ababa has said it will start to fill the dam whether or not a deal is agreed. Abdel Fattah al-Sisi, the Egyptian president, previously said Egypt would take all necessary measures to protect its rights to the Nile water, while Abiy Ahmed, the Ethiopian prime minister, has said his country was ready to “mobilize millions” to defend the dam.

In May, Egypt called on the United Nations Security Council to press Addis Ababa to come to a deal. “The unilateral filling and operation of this dam, without an agreement that includes the necessary precautions to protect downstream communities … would heighten tensions and could provoke crises and conflicts that further destabilize an already troubled region,” said Sameh Shoukry, the Egyptian foreign minister, in a speech to the Security Council in late June.

Both governments describe the issue as “existential ” for their people. But despite the at-times aggressive rhetoric, “I don’t think there is any consideration of military action being taken seriously”, said Hafsa Halawa, non-resident at the Middle East Institute, a US think-tank.

The hydropower project will have the capacity to generate 6,000 megawatts of electricity, making it Africa’s large st. The dam is seen by Ethiopia as a linchpin of its development plans, allowing it to bring electricity to tens of millions of its people. Ethiopia has rejected the notion that Egypt has “historic water rights” or that “current use” can be used as a guide to how much water the downstream country should receive. But in Egypt, a country with a population of 100m that is totally reliant on the Nile for water, there is deep alarm over future shortages as unfettered control of the flow of water passes to Ethiopia.