Ob River
— Noun
– English
～ a major river of western Siberia; flows generally northward and westward to the Gulf of Ob and the Kara Sea
Orinoco River
— Noun
– English
～ a South American river 1,500 miles long; flows into the South Atlantic
Orange River
— Noun
– English
～ a river in South Africa that flows generally westward to the Atlantic Ocean
Ottawa river
— Noun
– English
～ a river in southeastern Canada that flows along the boundary between Quebec and Ontario to the Saint Lawrence River near Montreal
Ouachita River
— Noun
– English
～ a river that rises in western Arkansas and flows southeast into eastern Louisiana to become a tributary of the Red River
Ouse River
— Noun
– English
～ a river in northeastern England that flows generally southeastward to join the Trent River and form the Humber
Osage River
— Noun
– English
～ a river in Missouri that is a tributary of the Missouri River
Ohio River
— Noun
– English
～ a river that is formed in western Pennsylvania and flows westward to become a tributary of the Mississippi River
Oder River
— Noun
– English
～ a European river; flows into the Baltic Sea