A river's water can fluctuate over time. Understanding the hydrological cycle is useful in order to understand how and why the amount of water fluctuates.
A drainage basin is the area of land around the river that is drained by the river and its tributaries.
- Watershed - the area of high land forming the edge of a river basin
- Source - where a river begins
- Mouth - where a river meets the sea
- Confluence - the point at which two rivers meet
- Tributary - a small river or stream that joins a larger river
- Channel - this is where the river flows