Question: The Isla Vizcaíno is an island in Uruguay located on the estuary of the Yaguarí creek, the northern arm of the estuary of the Río Negro (Uruguay) of which river in South America, that flows from north to south and forms parts of the boundaries of Brazil, Argentina, and Uruguay, separating some of the Argentine provinces of La Mesopotamia from the other two countries?
{'answer': 'Uruguay River', 'supporting_facts': [['Vizcaíno Island', 0], ['Uruguay River', 0]]}