How can a river below a dam or impoundment be considered “free-flowing?”

Section 16(b) of the Wild & Scenic Rivers Act, defines a “river” as “a flowing body of water . . . or portion, section, or tributary thereof. . . .”  “Free-flowing” is defined as “existing or flowing in natural condition without impoundment. . . .”  Therefore, any section of river with flowing water meets the technical definition of free flowing, even if impounded upstream.

Source
Interagency Wild & Scenic Rivers Council