Longest river tributary

- Who
- Madeira tributary
- What
- 3380 kilometre(s)
- When
- 01 January 0001
The largest river basin in the world is that drained by the Amazon, which covers about 7,045,000 km² (2,720,000 miles²). It has countless tributaries, including the Madeira, which at 3,380 km (2,100 miles) is the longest tributary in the world, being surpassed by only 17 other rivers.