The Grand Ethiopian Renaissance Dam under construction in 2017 (courtesy of Salini Impregilo).

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Ethiopia is building Africa's largest dam -- the Grand Ethiopian Renaissance Dam

Situated on the Blue Nile, the dam could threaten Egypt's water supply

Already facing water shortages, Egypt is desperate to maintain its dominance of the River Nile

CNN  — 

Look at Egypt on Google Earth and you will see a green line snaking through a sand-colored landscape, fanning out into a triangle in the north.

This emerald ribbon is the vegetation that grows on either side of the Nile River and around its delta. It is Egypt’s only fertile land – and testament to the country’s reliance on this fabled waterway.

The Nile River Basin extends to 11 African countries, but Egypt – one of the oldest civilizations in the world – has controlled the river and used the lion’s share of its waters for millennia.

That could be about to change.

Ethiopia’s very big dam