A river begins its journey far from the sea, often high in the mountains or hills where rain and melting snow gather into small streams. These streams trickle downhill, joining with others, and gradually grow wider and stronger as they travel.

As a river flows, it shapes the land around it. Over hundreds or even thousands of years, moving water can carve deep valleys, smooth rocks, and carry soil from one place to another. This process, known as erosion, slowly transforms the landscape.

Eventually, most rivers empty into a larger body of water, such as a lake or an ocean, at a point called the mouth of the river. By the time it reaches its mouth, a river may look nothing like the tiny stream it once was.