waters of the United States (WOTUS)

As defined in the Clean Water Act, “waters of the United States” (WOTUS) are surface waters, such as streams, rivers, lakes, estuaries, coastal waters and wetlands, and generally include interstate waters used in commerce and their tributaries, waters that are traditionally navigable, coastal waters, and any adjacent wetlands to those waters.  Whether a water body is protected under this definition is not always easy, and can change due to court rulings, new regulations, or modifications to the Act.  The Clean Water Act does not regulate groundwater.

For more information: http://water.epa.gov/lawsregs/guidance/wetlands/CWAwaters.cfm