Which country contains the source of the Blue Nile?

The Nile has two main branches. The White Nile emerges from the East African lakes and provides a steady year-round flow, while the Blue Nile rises at Lake Tana in the Ethiopian highlands and plunges down through gorges to meet the White Nile at Khartoum. It is the Blue Nile that supplies the great majority of the water reaching Egypt during the flood season, because the Ethiopian highlands catch the summer monsoon rains and shed them in a torrent, carrying with them the dark, fertile silt that built the Egyptian floodplain and made its agriculture possible for thousands of years. The ancient Egyptians could measure the flood without ever knowing where it came from. That dependence is why the river remains politically charged today, with the countries along it negotiating hard over how the Blue Nile's flow is stored and released upstream.

The Blue Nile's summer surge is what gave the ancient Egyptian calendar its flood season, timed by the river rather than by rainfall in Egypt.