South America's Three Longest Rivers

1. Amazon River — ~6,400 km (4,000 mi). Source: Andes (Peru). Traverses Peru, Brazil, Bolivia, Ecuador, Colombia, Venezuela, Guyana. World's largest by discharge (209,000 m³/s).
2. Paraná River — ~4,880 km (3,030 mi). Source: Confluence of Paranaíba & Grande (Brazil). Traverses Brazil, Paraguay, Argentina. Forms Río de la Plata estuary with Uruguay River.
3. São Francisco River — ~2,900 km (1,800 mi). Source: Serra da Canastra (Brazil). Entirely within Brazil. "River of National Unity"—key for NE Brazil hydro, irrigation, navigation.

Note: The Madeira (Amazon tributary) at ~3,250 km would rank 3rd if counted separately. The Purus and Japurá also exceed 2,500 km. The Amazon system dominates continental hydrology.