The Nile is traditionally considered the longest river in the world, measuring about 6,650 kilometres from its most distant source to the Mediterranean Sea.
The river flows northward through northeastern Africa and crosses or drains eleven countries, including Uganda, South Sudan, Sudan and Egypt. Its two principal tributaries are the White Nile and Blue Nile. The White Nile begins in the Great Lakes region, while the Blue Nile rises in Ethiopia.
The Blue Nile contributes most of the Nile’s water and carries fertile sediment from the Ethiopian Highlands. The two branches meet at Khartoum in Sudan before the combined river continues north through Egypt.
The Amazon is sometimes argued to be longer, depending on which sources and measurements are used. However, the Nile remains the conventional answer in many reference works and general-knowledge questions.