What makes this river so much fun to raft?

This raft trip is on the Gallatin River in Montana. The river is fast because its in the mountains traveling down a steep slope. There is lots of water because it’s early summer. The snow from up higher is melting. Did you ever go whitewater rafting? It’s fun!

What Are Streams and Rivers?

stream is a body of freshwater that flows downhill in a channel. The channel of a stream has a bottom, or bed, and sides called banks. Any size body of flowing water can be called a stream. Usually, though, a large stream is called a river.

Features of Streams and Rivers

All streams and rivers have several features in common. These features are shown in the Figure below. The place where a stream or river starts is its source. The source might be a spring, where water flows out of the ground. Or the source might be water from melting snow on a mountain top, like the stream pictured in the Figure below. A single stream may have multiple sources.

A stream flows fast and steep where it originates in the mountains. This stream, in Glacier National Park in Montana, is coming from snow melt. [2]

Water in a stream flows along the ground from higher to lower elevation. What force causes the water to keep flowing? [3]

A stream or river probably ends when it flows into a body of water, such as a lake or an ocean. A stream ends at its mouth. As the water flows into the body of water, it slows down and drops the sediment it was carrying. The sediment may build up to form a delta.

Several other features of streams and rivers are also shown in Figure above.

  • Small streams often flow into bigger streams or rivers. The small streams are called tributaries. A river and all its tributaries make up a river system.
  • At certain times of year, a stream or river may overflow its banks. The area of land that is flooded is called the floodplain. The floodplain may be very wide where the river flows over a nearly flat surface.
  • A river flowing over a floodplain may wear away broad curves. These curves are called meanders. You can see an example of this in the Figure below.

A river meanders across an estuary in South Carolina. [4]

River Basins and Divides

All of the land drained by a river system is called its basin, or watershed. One river system’s basin is separated from another river system’s basin by a divide.  The divide is created by the highest points between the two river basins. Precipitation that falls within a river basin always flows toward that river. Precipitation that falls on the other side of the divide flows toward a different river. A continental divide separates rivers that flow into different oceans.

The Figure below shows the major river basins in the U.S.

River basins in the U.S. [5]


  • continental divide: A divide that separates water that goes to different oceans.
  • divide: A ridge that separates one water basin from another.
  • floodplain: The region near a stream where water overflows during floods.
  • headwaters: The location where a stream forms, often high in the mountains.
  • meander: A bend in a stream channel.
  • mouth: Where a stream enters a larger body of water such as a lake or an ocean.
  • source: Where a stream begins; usually in mountains.
  • stream: A body of moving water, contained within a bank (sides) and bed (bottom).
  • tributary: The smaller of two streams that join together to make a larger stream.
  • watershed: All of the land area that is drained by a river and its tributaries.


  • A moving body of water of any size is a stream. A river is a large stream.
  • A tributary begins at its headwaters on one side of a divide. Two tributaries come together at a confluence.
  • A river ends at an estuary. If the river drops sediment, it may create a delta.


Use these resources to answer the questions that follow.

Streams and Rivers at http://www.youtube.com/watch?v=TxI9gTvNY0M(3:45)

  1. Where is water speed and weight the greatest?
  2. What is created by this fast moving water?
  3. Explain what is occurring where the water moves slowly.

Minnesota River Sediment at http://www.youtube.com/watch?v=FvZcDTFXguY (2:59)

  1. What has destabilized the Minnesota River area?
  2. What speeds up the water as it moves down the river?
  3. What caused the ravines to form?
  4. Where does most of the sediment end up?
  5. List the sources of the sediment.


  1. Describe the features of a river from where it begins to where it ends.
  2. What happens to two drops of water that fall on opposite sides of a divide?
  3. Why does a tributary not cross over a divide?

Image Attributions

  1. ^ License: CC BY-NC 3.0
  2. ^ Credit: Miles Orchinik; License: CC BY-NC 3.0
  3. ^ Credit: CK-12 Foundation – Hana Zavadska; License: CC BY-NC 3.0
  4. ^ Credit: Image copyright John Wollwerth, 2012; License: CC BY-NC 3.0
  5. ^ Credit: Courtesy of the National Weather Service; License: CC BY-NC 3.0

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