What is the name of the longest river in South America?

The Amazon River is recognized as the longest river in South America and is often cited as the second longest river in the world, depending on measurement methods used in comparison with the Nile. The Amazon flows through multiple countries, including Peru, Colombia, and Brazil, and is known for its vast ecosystem and biodiversity. This river is integral to the climate and environment of the region, significantly influencing the rainfall patterns and serving as a crucial waterway for both transportation and wildlife.

Other options, like the Nile, Yangtze, and Mississippi rivers, while significant in their own rights, do not traverse South America and are located in different continents. The Nile is primarily in northeastern Africa, the Yangtze is in China, and the Mississippi runs through the United States, thus making them irrelevant to the question regarding the longest river in South America.