Plata, Río de la

Estuary on the South Atlantic coast of South America, at the border between Argentina and Uruguay; it is formed by the confluence of the Paraná and Uruguay rivers; length 275 km/171 mi; width at mouth 225 km/140 mi; drainage basin area 3,900,000 sq km/1,505,790 sq mi. The basin drains much of Argentina, Bolivia, Brazil, Uruguay, and Paraguay. Its shores are densely populated; Buenos Aires lies on the southern shore and Montevideo is situated on the northern shore. The estuary was encountered in 1516 by the Spaniard Juan Díaz de Solís in his attempts to find a route to the Pacific Ocean.