Niagara River vs river

Niagara River and river both are nouns.

Word	Noun	Adjective	Verb	Adverb
Niagara River	Yes	No	No	No
river	Yes	No	No	No

Niagara River (noun)	river (noun)
a river flowing from Lake Erie into Lake Ontario; forms boundary between Ontario and New York	a large natural stream of water (larger than a creek)