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US Geological Survey
Earth's Water: Rivers and Streams
The USGS explains the definition of a river and how a river is supplied with water. Included is a cross section of a river. Click Home to access the site in Spanish.
CK-12 Foundation
Ck 12: Earth Science: Water Pollution
[Free Registration/Login may be required to access all resource tools.] Describes the sources of water pollution, such as municipal, industrial, and agricultural.