The Amazon River has the highest discharge of any river in the world. Discharge measures the volume of water flowing past a point over time, and the Amazon releases roughly 200,000 to 220,000 cubic metres of water per second into the Atlantic Ocean on average.
That extraordinary flow comes from the Amazon Basin, which covers about 7 million square kilometres across Brazil and several neighbouring South American countries. Heavy rainfall, enormous tributaries and a vast network of wetlands feed the main river. Major tributaries include the Rio Negro, Madeira, Tapajós and Xingu.
This question is about volume of flow, not length. The Nile is often described as the world’s longest river, although length rankings can depend on how sources and tributaries are measured. The Congo is generally considered the second-largest river by discharge, but the Amazon carries more than four times as much water in many comparisons. The river’s huge outflow can affect Atlantic salinity far offshore.