river vs Lower Tunguska

river and Lower Tunguska both are nouns.

Word	Noun	Adjective	Verb	Adverb
river	Yes	No	No	No
Lower Tunguska	Yes	No	No	No

river (noun)	Lower Tunguska (noun)
a large natural stream of water (larger than a creek)	a river that arises to the north of Lake Baikal and flows north and west to the Yenisei River