Geographically and hydrologically, there is only one Amazon River, which flows through South America and is widely considered the largest river in the world by discharge volume. However, the question often arises because the Amazon is a massive river system comprised of more than 1,100 tributaries, many of which are massive rivers in their own right, such as the Madeira, the Negro, and the Xingu. Furthermore, scientists in 2011 announced the discovery of the Hamza River, a "subterranean twin" to the Amazon that flows roughly 4,000 meters beneath the surface. While the Hamza follows a similar path toward the Atlantic, it moves much slower and is technically an underground aquifer system rather than a "river" in the traditional sense. In 2026, environmentalists often speak of the "many Amazons" in a metaphorical sense to describe the diverse ecosystems within the basin—the flooded forests (Varzea), the dry land forests (Terra Firme), and the blackwater and whitewater regions—all of which are interconnected but distinct parts of the single, life-giving artery of the South American continent.