Water flows downhill under gravity, collecting into channels. A river is a natural watercourse that carries water and sediment from higher to lower elevations, ultimately emptying into an ocean, lake, or another river. The network of tributaries forms a drainage basin.

Rivers shape landscapes through erosion, transport, and deposition. They supply freshwater for drinking, irrigation, and industry. Floodplains provide fertile soil but also flood risk. Many of the world’s great cities grew up on riverbanks for water supply and transport.

Dams, diversions, and pollution have altered most major rivers. Restoration projects now seek to reestablish more natural flow regimes and habitats. The continuous movement of water from source to mouth remains one of the most visible and vital processes on the planet’s surface.

• Natural flowing watercourse
• Transports water and sediment
• Shapes land through erosion and deposition
• Critical for human water supply and settlement