Yes!........ Congratulations 'nwspence' you are quite correct. Your Honorary 'Gold Medal' is on its way. (answered just before the 1st Hint)........ well done.
THE SOLVE:.......The initial letters of the Capitals and / or Countries read B-U-C-H-A-R-E-S-T (Brazil / Ulaan Bator / etc. etc.) The River running through Bucharest is the 'Dambovita'....... the correct answer: