What is the largest river basin in the world?

The Amazon basin is the largest river basin in the world. It covers roughly 7 million square kilometres across South America and drains water eastward into the Atlantic Ocean.

The basin includes Brazil, Peru, Colombia, Bolivia, Ecuador, Venezuela, and Guyana, although Brazil contains the largest share. Thousands of tributaries feed the Amazon system, including the Negro, Madeira, Purus, Juruá, Ucayali, and Marañón rivers. Together, they drain an area covering about 40% of South America.

The Amazon is also the world's largest river by discharge. It releases more freshwater into the ocean than any other river, accounting for a substantial share of global river discharge. Seasonal flooding creates vast várzea, or floodplain forests, that support exceptionally rich wildlife and plant life.

The answer is sometimes confused with the world's longest river, a title disputed between the Amazon and the Nile depending on how sources and headwaters are measured. That is a different measurement from basin area: by drainage-basin size, the Amazon is the clear leader.