In the 1950s, Egypt and Britain played an old version of tit-for-tat. Egypt took the Suez Canal. The British decided to pay them back by stealing the river Nile itself. Yes, the whole Nile.
The Suez Canal connects the Mediterranean Sea and the Red Sea, saving boats that go through it a considerable length of time – roughly the time it takes to sail around Africa. It's a valuable piece of infrastructure, so it was not a surprise that, in the 1950s, the British were not pleased to lose control of it to the Egyptians. A military attempt, made jointly with France and Israel, to take it back failed, and brought about the disapproval of the wider world. Since the military option having failed, the British were left wondering what other options they had. Along with the CIA they came up with an idea that was equal parts science fiction trope and cartoon trope. They'd shut off the Nile.
While the British didn't control Egypt anymore, they did have pull in Uganda, in the form of the Owen Falls dam. This dam controlled the flow of the White Nile, one of the tributaries to the main river, and it could be adjusted to block different amounts of water. Enough oomph, and the Owen Falls Dam could cut eighty percent of the water for the Egyptian Nile. This plan went all the way to the Prime Minister's office, at which point people brought up a few problems. First of all, the value of the Nile in Egypt came mainly from the annual floods of the river, not the presence of the river itself. Nothing major would happen for about 18 months. Secondly, while it could economically cripple Egypt, it wouldn't starve anyone (and yes, this was considered a problem). At least, it wouldn't starve anyone in Egypt. But the relatively friendly nations of Uganda and Kenya wouldn't stay friendly for long after their water was cut off. Ultimately, the plan was scrapped.