river vs Ob River

river and Ob River both are nouns.

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

river (noun)	Ob River (noun)
a large natural stream of water (larger than a creek)	a major river of western Siberia; flows generally northward and westward to the Gulf of Ob and the Kara Sea