The Amazon River flows for more than 6,600 km, and with its hundreds of tributaries and streams contains the largest number of freshwater fish species in the world. Equally impressive are the unfathomable numbers of mammals, birds, amphibians, and reptiles4 found across the biome.

The Amazon River is unique due to its staggering scale and its role as the Earth's "biological heart." It is the largest river in the world by discharge volume; it pumps roughly 209,000 cubic meters of freshwater into the Atlantic Ocean every second—more than the next seven largest rivers combined. This flow is so massive that it creates a "freshwater plume" in the ocean that can be detected hundreds of miles from the coast. Geologically, it is special because it once flowed backwards (from east to west) toward the Pacific, only reversing its course roughly 10 million years ago after the rise of the Andes Mountains. In 2026, it is also celebrated for its "Flying Rivers"—a phenomenon where the rainforest's trees release 20 billion tonnes of moisture into the atmosphere daily, creating a self-sustaining weather system that regulates rainfall across all of South America. Additionally, the river is home to over 3,000 known species of fish, including the iconic pink river dolphin and the predatory piranha, representing the highest freshwater biodiversity on the planet.