Which Amazon River tributary is its largest by water discharge?

The Madeira River is the Amazon River’s largest tributary by water discharge.

It forms in Bolivia at the confluence of the Mamoré and Beni rivers, then flows northward along or near the Bolivia–Brazil border before entering the Amazon system in Brazil. The Madeira is one of South America’s major rivers and drains a vast area of the southwestern Amazon Basin.

The river transports enormous quantities of water and sediment. Its basin includes parts of Bolivia, Brazil, and Peru, and its network of tributaries links Andean headwaters with the lowland rainforest. Seasonal changes in rainfall strongly influence its water level and current.

The Negro River is another immense Amazon tributary and is famous as the world’s largest blackwater river by volume, but it is not the largest Amazon tributary by discharge. The Madeira has also been the site of major hydroelectric projects, including the Santo Antônio and Jirau dams in Brazil.