Great rivers

Measurements of river lengths vary according to where the river is said to begin. So some people say that Africa's Nile is the world's longest river; others say that South America's Amazon is longer.

The source of the Amazone was only discovered in 1971, in snowbound lakes high in the Andes. It is named Laguna McIntyre after the American who found it.

If the full length of the Amazon is counted, it is 6750 km long compared with the Nile at 6670 km. The Amazon basin covers more than 7 million sq hm. The third longest river is China's Yangtse, with 6300 km.

The world's longest tributary is the Madeira flowing into the Amazon. At 3880 km long it is the 18th longest river in the world.

The world's longest estuary is that of the Ob in Russia, which is up to 80 km wide and 885 km long. The Ob is the biggest river to freeze solid in winter.

The shortest official river is the North Fork Roe River in Montana, USA, which is just 17.7 m long.