All of the land surface area that drains water into a particular river or its tributaries is called a river basin. A river basin might be thought of as a giant bowl, or basin. The force of gravity pushes all of the water that goes into a bowl down the sides and toward the lowest point in that bowl. At the bottom of the bowl, the drained water from the edges of the bowl collects and forms a single body of water. In a river basin, much of the water that drains off the land finds its way to the river, often through creeks and streams.
The creeks and streams that drain into a river are known as tributaries. These all come together to form a river, which drains into in a larger body of water, such as another river, a lake, a gulf or an ocean. The river basin is made up of all the land drained by a river and its tributaries. Rain that falls on the land making up a river basin collects and drains to the lowest point of that particular piece of land.
Neighborhoods, forests, mountains and cities can all be located in a river basin. When it rains and the ground can no longer absorb rainwater, it forms small rivulets which then drain into larger bodies of water, such as streams, rivers and lakes. All of the pollutants and anything else that might be on the ground and can be carried by the water might be washed into the river and eventually out to sea.
Watersheds are slightly different from river basins. A watershed is small part of a river basin and might drain only into a specific body of water. A large number of watersheds can exist within the boundaries of a river basin.
All of the living and non-living things within the ecosystem of a river basin are connected to one another. When one part of the river basin is disturbed, the entire ecosystem is affected in some way. This interdependent balance must be maintained to preserve the balance of the entire river basin ecosystem and its inhabitants.
The unique topography of a river basin makes each one unique. For example, some are made up of high granite walls and steep hills or mountains. This steep and mountainous terrain can make a river flow quickly over many rocks and around sharp bends, creating lots of churning white water rapids. By contrast, other river basins contain relatively flat land. The topography of the Mississippi River basin, for example, allows its waters to flow smoothly and peacefully, curving across large expanses of land.