The Amazon River (US pron.: // or UK //; Spanish and Portuguese: Amazonas) in South America is the second longest river in the world and by far the largest by waterflow with an average discharge greater than the next seven largest rivers combined (not including Madeira and Rio Negro, which are tributaries of the Amazon). The Amazon, which has the largest drainage basin in the world, about 7,050,000 square kilometres (2,720,000 sq mi), accounts for approximately one-fifth of the world's total river flow.
The geography of South America contains many diverse regions and climates. Geographically, South America is generally considered a continent forming the southern portion of the American landmass, south and east of the Panama–Colombia border by most authorities, or south and east of the Panama Canal by some. South and North America are sometimes considered a single continent or supercontinent, while constituent regions are infrequently considered subcontinents. Geopolitically and geographically, all of Panama—including the segment east of the Panama Canal in the isthmus—is generally considered a part of North America alone and among the countries of Central America.
South America became attached to North America only recently (geologically speaking) with the formation of the Isthmus of Panama some 3 million years ago, which resulted in the Great American Interchange. The Andes, likewise a comparatively young and seismically restless mountain range, run down the western edge of the continent; the land to the east of the northern Andes is largely tropical rain forest, the vast Amazon River basin. The continent also contains drier regions such as eastern Patagonia and the extremely arid Atacama desert.