The world’s longest rivers are defined as the longest natural streams whose water flows within a channel, or streambed, with defined banks. They tend to have extensive river systems, which include tributaries to the main river channel, that drain large portions of Earth’s continents. Accurate comparable river-length measurements, however, are often difficult to obtain,
because stream definitions and measurement standards vary between countries. It is possible that the main channels of well over 100 of the greatest rivers may exceed 1,600 km (about 1,000 miles) in length.
Measuring from the headwaters of the most distant source, the five longest rivers in the world are the Nile (in eastern and northeastern Africa), the Amazon–Ucayali–Apurímac (in South America), the Yangtze (in China), the Mississippi–Missouri–Red Rock (in the United States), and the Yenisey–Baikal–Selenga (in northern Asia).
