As used in this part:

(a) “Free flowing” means existing or flowing in natural condition without impoundment, diversion, straightening, riprapping, or other modification.

(b) “Natural river” means a river that has been designated by the department for inclusion in the wild, scenic, and recreational rivers system.

(c) “River” means a flowing body of water or a portion or tributary of a flowing body of water, including streams, creeks, or impoundments and small lakes thereon.

(d) “System” means all of those rivers or portions of rivers designated under this part.