Estuary of the 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 25–28 mi (40–45 km) wide. Discovered by the Spanish in 1516, it was explored by {{link=Magellan, Ferdinand">Ferdinand Magellan in 1520 and by Englishman Sebastian Cabot (1527–29). The first permanent settlement in the area was at Asunción in 1537.