Which Amazonian river is the world’s largest blackwater river by volume?

The Negro River is the world’s largest blackwater river by volume.

The Negro flows through Colombia, Venezuela and Brazil before joining the Solimões near Manaus to form the Amazon River. Its dark appearance comes largely from dissolved organic matter, including tannins leached from vegetation and soils in its drainage basin. The water is generally acidic and nutrient-poor compared with the pale, sediment-rich water of the Solimões.

The river is about 1,400 kilometres long and drains a huge area of northern Amazonia. Its floodplain supports specialised forests and aquatic communities adapted to seasonal changes in water level. The Anavilhanas archipelago, one of the world’s largest river archipelagos, lies in the lower Negro.

Blackwater does not mean the river is polluted or literally black. The contrast with the muddy Solimões is especially visible near Manaus, where the two flows run alongside one another for several kilometres before mixing. This is separate from the broader Meeting of Waters attraction.