Caramoran River, Manzi, China (Google Maps ⧉, OpenStreetMap ⧉)

"Concerning the Great River Caramoran and the City of Cachanfu. When you leave the castle, and travel about 20 miles westward, you come to a river called Caramoran, so big that no bridge can be thrown across it."

"At the end of those three days you reach the great river Caramoran, which flows hither from Prester John’s country."