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?

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Uruguay River pulp mill dispute: The pulp mill dispute was a dispute between Argentina and Uruguay concerning the construction of pulp mills on the Uruguay River.  The presidents at the time were Néstor Kirchner (Argentina) and Tabaré Vázquez (Uruguay).  As a diplomatic, economic, and public relations conflict between both parties, the dispute has also affected tourism and transportation as well as the otherwise amicable relations between the two countries.  The feud was unprecedented between the two countries, which have shared historical and cultural ties.  Proceedings were brought before the International Court of Justice as a case formally named Pulp Mills on the River Uruguay "(Argentina v. Uruguay)".  It ruled that, although Uruguay failed to inform Argentina of the operations, it did not pollute the river, so closing the pulp mill would be unjustified.  The conflict ended in 2010, during the presidencies of Cristina Fernández de Kirchner (Argentina) and José Mujica (Uruguay), with the establishment of a joint coordination of the activities in the river.

Platine War: The Platine War (18 August 1851 – 3 February 1852) was fought between the Argentine Confederation and an alliance consisting of the Empire of Brazil, Uruguay and the Argentine provinces of Entre Ríos and Corrientes.  The war was part of a long-running interest disputes between Argentina and Brazil for influence over Uruguay and Paraguay, and hegemony over the Platine region (areas bordering the Río de la Plata).  The conflict took place in Uruguay, on the Río de la Plata, and northeastern Argentina.  Uruguay's internal troubles, including the long-running Uruguayan Civil War, ""La Guerra Grande"" (The Great War), were heavily influential factors leading to the Platine War.

Vizcaíno Island: 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 the Uruguay River.  It is bordered by the South Black River on the East and the Vizcaíno creek to the east, the Uruguay River to the North and the Arroyo Yaguarí on the West.

Río de la Plata: The Río de la Plata (] , "River of Silver") — rendered River Plate in British English and the Commonwealth and La Plata River (occasionally Plata River) in other English-speaking countries — is the river and estuary formed by the confluence of the Uruguay and the Paraná rivers.  It empties into the Atlantic Ocean, forming a funnel-shaped indentation on the southeastern coastline of South America.  Depending on the geographer, the "Río de la Plata" may be considered a river, an estuary, a gulf or a marginal sea.  For those who consider it a river—as is the case in most of Argentina and Uruguay—it is the widest river in the world, with a maximum width of about 220 km .

Río Negro (Uruguay): The Río Negro (] , "Black River") is the most important river in Uruguay.  It originates in the southern highlands of Brazil, just east of Bagé, and flows west across the entire width of Uruguay to the Uruguay River.  The course of the Río Negro across Uruguay effectively divides the south of the country from the north.  The Río Negro's principals tributaries are Yí River and Tacuarembó River.

Argentina–Uruguay border: The Argentina–Uruguay border is a line of 579 km marked by the Uruguay River, and is the border between Argentina and Uruguay.  It starts in a triple border Argentina-Uruguay-Brazil, at the mouth of the Quaraí River in the Uruguay.  The course follows the Uruguay river, passing west of the Uruguayan departments of Artigas, Salto, Paysandu, Rio Negro, Soriano and Colonia and the Argentine provinces of Corrientes, Entre Rios and Buenos Aires, until the confluence of the Uruguay and the Paraná rivers into the Rio de la Plata.

Río Negro Department: Río Negro Department (Spanish: "Departamento de Río Negro" , ] ) is a department of the northwestern region of Uruguay.  It has an area of 9282 km2 and a population of 54,765.  Its capital is Fray Bentos.  It borders Paysandú Department to the north, Tacuarembó Department to the east, Durazno Department to the southeast, Soriano Department to the south and has the Río Uruguay flowing at its west, separating it from Argentina.

Chixoy River: The Chixoy River or Río Negro is a river in Guatemala.  The river is called Río Negro from its sources in the highlands of Huehuetenango and El Quiché until it reaches the Chixoy hydroelectric dam (located at ), where the Río Salamá and Rio Carchela converge with the Río Negro.  After the Chixoy dam, the river is called Río Chixoy and flows northwards, marking the departmental limits between Alta Verapaz and El Quiché, until it reaches the border with Mexico.  From there on it continues along the border for another 113 km as the Salinas river until it finally converges with the Río la Pasión (at ) to form the Usumacinta river which flows into the Gulf of Mexico.

Uruguay River: The Uruguay River (Spanish: Río Uruguay , ] ; Portuguese: Rio Uruguai , ] ) is a river in South America.  It 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.  It passes between the states of Santa Catarina and Rio Grande do Sul in Brazil; forms the eastern border of the provinces of Misiones, Corrientes, and Entre Ríos in Argentina; and makes up the western borders of the departments of Artigas, Salto, Paysandú, Río Negro, Soriano, and Colonia in Uruguay.

Uruguay: Uruguay ( ; ] ), officially the Oriental Republic of Uruguay (Spanish: "República Oriental del Uruguay" ), is a sovereign state in the southeastern region of South America.  It borders Argentina to its west and Brazil to its north and east, with the Río de la Plata (River of Silver) to the south and the Atlantic Ocean to the southeast.  Uruguay is home to an estimated /1e6 round 2 million people, of whom 1.8 million live in the metropolitan area of its capital and largest city, Montevideo.  With an area of approximately 176000 km2 , Uruguay is geographically the second-smallest nation in South America, after Suriname.

Supporting paragraphs: Vizcaíno Island Uruguay River
Answer: Uruguay River