While there is some debate about its length, the river is generally believed to be at least 4,000 miles (6,400 km) long, which makes it the second longest river in the world after the Nile River in Africa. The Amazon is also famous for the rainforest found along its shores.

Whether the Amazon is the first or second "largest" depends entirely on how you define "large": length vs. volume. For over a century, the Nile was traditionally considered the longest at 4,132 miles, with the Amazon second at 3,976 miles. However, in 2026, the scientific consensus has shifted significantly following new expeditions to the Peruvian Andes. Many researchers now argue the Amazon is actually the longest, measuring approximately 4,345 miles, surpassing the Nile's 4,258 miles. Regardless of the length debate, the Amazon is indisputably the largest by volume. It carries more water than the next seven largest rivers combined, accounting for roughly 20% of the world’s river-to-ocean freshwater discharge. It is also the widest river in the world; during the wet season, parts of it swell to over 25 miles wide, whereas the Nile remains relatively narrow throughout its course. So, while it may still be called the "second longest" in older textbooks, in terms of sheer scale, water output, and drainage basin, the Amazon is the unchallenged giant of the planet.