The water column refers to just the water in a river or stream, exclusive of its channel (path) or banks. All the world's rivers and streams combined contain less than 1 percent of all the water on Earth. Most water is held in the oceans.

Braided streams of the Firth River in Canada reflecting the sunlight. (Reproduced by permission of Corbis. Photograph by Lowell Georgia.)

Composition

Rivers and streams carry fresh water, but this water may be clear or cloudy, polluted or clean. What determines its characteristics are where it originates and the nature of its channel.

As the water moves across the land, particles of rock, soil, and decaying plant or animal matter, called sediment, become suspended in it. An average of 0.13 ounces per gallon (100 milligrams per liter) of material is suspended in rivers in humid regions of the United States, and as much...