Río de la Plata

The upper river contains several islands, including Oyarvide Island and the Solís Islands in Argentine waters and Juncal Island, Islote el Matón, Martín García Island and Timoteo Domínguez Island in Uruguayan waters. Because of deposition of sediments from the heavy stream load carried down from the river's tributaries, the islands in the Río de la Plata generally grow over time.

A submerged shoal, the Barra del Indio, divides the Río de la Plata into an inner freshwater riverine portion and an outer brackish estuarine portion.[6] The shoal is located approximately between Montevideo and Punta Piedras (the northwest end of Samborombón Bay). The inner fluvial zone is about 180 kilometres (110 mi) long and up to 80 kilometres (50 mi) wide, with a depth which varies from about 1 to 5 metres (3.3 to 16.4 ft); the depth of the outer estuary zone increases from 5 to 25 metres (16 to 82 ft).[6] The river's discharge is strong enough to prevent saltwater from penetrating to the inner portion.[7]

Satellite image of the Paraná and Uruguay rivers emptying into the Río de la Plata. Due to the relatively calm surface of the estuary and the angle of the Sun relative to the satellite, the current of the river flowing out into the Atlantic is visible.

The Río de la Plata's drainage basin (sometimes called the Platine basin or Platine region)[8][9] is the 3,170,000-square-kilometre (1,220,000 sq mi)[3] hydrographical area that drains to the Río de la Plata. It includes areas of southeastern Bolivia, southern and central Brazil, the entire country of Paraguay, most of Uruguay, and northern Argentina. Making up about one fourth of the continent's surface, it is the second largest drainage basin in South America (after the Amazon basin) and one of the largest in the world.[4]

The main rivers of the La Plata basin are the Paraná River, the Paraguay River (the Paraná's main tributary), and the Uruguay River.[6]

The Paraná River's main tributaries include the Paranaíba River, Grande River, Tietê River, Paranapanema River, Iguazu River, Paraguay River, and the Salado River, after which it ends in the large Paraná Delta. The Paraguay River flows through the Pantanal wetland, after which its main tributaries include the Pilcomayo River and the Bermejo River, before it ends in the Paraná. The Uruguay's main tributaries include the Pelotas River, Canoas River, Ibicuí River, and the Río Negro. Another significant tributary to the Río de la Plata is the Salado del Sur River.

The Río de la Plata was first explored by the Portuguese in 1512–13.[10][11] The Spanish first explored it in 1516, when the navigator Juan Díaz de Solís traversed it during his search for a passage between the Atlantic and the Pacific Oceans, calling it the Mar Dulce, or "freshwater sea."[3] The Portuguese navigator Ferdinand Magellan briefly explored the estuary in 1520 before his expedition continued its circumnavigation,[3] and in 1521 Cristóvão Jacques also explored the Plate River estuary and ascended the Parana River for the first time, entering it for about 23 leagues (around 140 km) to near the present city of Rosario.[12] The area was also visited by Francis Drake's fleet in early 1578, in the early stages of his circumnavigation.[13]

Explorer Sebastian Cabot made a detailed study of the river and its tributaries and gave it its modern name. He explored the Paraná and Uruguay rivers between 1526 and 1529, ascending the Paraná as far as the present-day city of Asunción, and also explored up the Paraguay River. Cabot acquired silver trinkets trading with the Guaraní near today's Asunción, and these objects (together with legends of a "Sierra de la Plata" in the South American interior brought back by earlier explorers) inspired him to rename the river "Río de la Plata" ("River of Silver").[3]

The first European colony was the city of Buenos Aires, founded by Pedro de Mendoza on 2 February 1536. This settlement, however, was quickly abandoned; the failure to establish a settlement on the estuary led to explorations upriver and the founding of Asunción in 1537. Buenos Aires was subsequently refounded by Juan de Garay on 11 June 1580.[3]

The city of Buenos Aires sits along the southern coast of the Río de la Plata.

During the colonial era, the Río de la Plata was made the center of the Governorate of the Río de la Plata. The Río de la Plata region, particularly Buenos Aires, was a significant site of trade throughout the 17th century. The Crown initially intended Buenos Aires to be a military establishment for the protection of the Potosí mines, but it soon became evident that a settlement large enough to provide military defense would attract trade. The primary export was silver from the mines of Potosí, and imports generally included European luxury goods, slaves, and sugar. This trade occurred outside of the fleet system authorized by the Spanish Crown, and therefore was generally considered "illicit." However, under the monarchy of the Spanish Habsburgs, the line between licit and illicit trade was quite blurry. Crown officials and military outposts in Buenos Aires often relied upon profits from illicit trade to support their administrative structures.[14]

Under the Bourbon monarchy, the governorate was elevated to the Viceroyalty of the Río de la Plata in 1776. This occurred as a result of the Bourbon Reforms, which attempted to restore the decaying wealth of the Spanish Crown. The reforms elevated the status of trade along the Río de la Plata and expanded what constituted "legal" trade so that the Crown could tax trade what had previously been "contraband." However, the plan did not go as intended. Although trade along the Río de la Plata flourished, very little silver was actually remitted to the Crown. Then, Spanish war with Britain and the simultaneous eruption of revolts in the mining regions of Peru led to a shortage of silver, putting strain on the merchant class of Buenos Aires. This caused a schism between merchants who wanted to try to continue reviving the Spanish Empire through silver trade and those who wanted to move on from silver and prioritize agricultural exports, ultimately tearing at the fabric of the Río de la Plata region's relationship with the Spanish Empire.[15]

In 1806 and 1807 the river was the scene of an important British invasion that aimed to occupy the area and was defeated by the local garrison and population.

Conflict in the region intensified after the independence of the former Spanish and Portuguese colonies in the first quarter of the 19th century. Interests in the territories and the navigation rights over the Platine region played a major role in many armed conflicts throughout the century, including the Argentine civil wars, the Cisplatine and Platine wars, and the Paraguayan War.[3] The river was blockaded by France and Britain in 1838–1840 and 1845–1850.

The naval battle during the Argentine-Brazilian War, 1827

During the Cisplatine War, the Battle of Juncal (named after Juncal Island) took place in the waters of the Río de la Plata from 8–9 February 1827 between squadrons of the newly independent United Provinces of the River Plate and the Brazilian Empire. The Argentines scored a decisive victory, capturing or destroying fifteen Brazilian vessels and losing none.[16]

In the first naval battle of the Second World War the German pocket battleship Admiral Graf Spee was engaged by the Royal Navy (RN) cruisers HMS Exeter and Ajax, and the Royal New Zealand Navy cruiser Achilles,[17] off the estuary of the River Plate in December 1939. The German ship retired up the estuary with a crippled fuel system and put into port at Montevideo. A few days later, rather than fight when believing himself outgunned, her captain scuttled her in the estuary. This engagement was part of the early Battle of the Atlantic.