Which river is the world's longest?

   The longest river in the world is the Nile, at 4,160 miles. It begins south of the equator in Burundi, flows north through Egypt, and drains into the Mediterranean Sea. Three tributaries are the principal sources of water for the Nile River: the Atbara (bringing water from Ethiopia and the Sudan), the Blue Nile (originating in Ethiopia), and the White Nile (collecting water from Tanzania, Rwanda, and Uganda). Ancient irrigation systems along the Nile River date back to 4000 B.C. The Aswan Dam, built in 1902, has been raised twice since then. The Aswan High Dam was finished in 1971, creating Lake Nassar. The Nile now irrigates more than 6 million acres of farmland in Egypt and the Sudan.
   The Amazon River in South America is 3,990 miles long; the Yangtze River in China is 3,400 miles long.