Estuary of the Paraná and Uruguay rivers, between Uruguay and Argentina.
It is about 170 mi (275 km) long, with a maximum width at its mouth of about 140 mi (220 km); at Montevideo it is about 60 mi (97 km) wide but narrows gradually to the northwest as it approaches Buenos Aires , where it is about 2528 mi (4045 km) wide. Discovered by the Spanish in 1516, it was explored by Ferdinand Magellan in 1520 and by Englishman Sebastian Cabot (152729). The first permanent settlement in the area was at Asunción in 1537.