Measuring a river's length sounds simple and is not. Where does it "start" — at which of several headstreams, measured in which season? Where does it "end" — at the coast, or out in a wide estuary where fresh and salt water mix? Small differences in these choices change the length by hundreds of kilometres, which is why published figures disagree.
The top ten (approximate lengths)
- Nile — about 6,650 km. Northeast Africa; flows north through Uganda, South Sudan, Sudan and Egypt to the Mediterranean. Its two main branches, the White Nile (from Lake Victoria) and the Blue Nile (from Ethiopia's Lake Tana), meet at Khartoum.
- Amazon — about 6,400 km, or longer by some surveys since 2007. South America; rises in the Peruvian Andes and crosses Peru, Colombia and Brazil. It carries by far the most water of any river — about a fifth of all the fresh water that reaches the world's oceans.
- Yangtze — about 6,300 km. The longest river that flows entirely within a single country (China).
- Mississippi–Missouri — about 6,275 km combined. The main drainage of the central United States.
- Yenisei–Angara–Selenge — about 5,540 km. Mongolia and Russia; drains into the Arctic Ocean.
- Yellow River (Huang He) — about 5,460 km. China; the "cradle of Chinese civilisation" and historically one of the most flood-prone rivers on Earth.
- Ob–Irtysh — about 5,410 km. China, Kazakhstan and Russia; another Arctic-draining Siberian system.
- Paraná–Río de la Plata — about 4,880 km. Brazil, Paraguay and Argentina.
- Congo–Chambeshi — about 4,700 km. Central Africa; the deepest river in the world, over 220 m in places, and second only to the Amazon in discharge.
- Amur–Argun — about 4,440 km. Forms much of the border between Russia and China.
Why the Nile–Amazon debate won't die
A 2007 Brazilian expedition traced a new Amazon source in a stream high in the Peruvian Andes and claimed a length that would make the Amazon the world's longest river. Other researchers dispute both the choice of source and the definition of the mouth — the Amazon's estuary is so wide (over 300 km) that it is unclear where the river ends and the ocean begins. Most references still list the Nile first, usually with a note that the Amazon may be longer.
Longest by continent
- Africa — Nile
- South America — Amazon
- Asia — Yangtze
- North America — Mississippi–Missouri
- Europe — Volga (about 3,530 km, entirely within Russia, draining to the Caspian Sea)
- Australia — Murray–Darling (about 3,670 km)
The other classic physical-geography list, with the same measurement subtleties.
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