The world’s widest “river” is mostly a silver estuary
The Río de la Plata—River Plate—forms where the Uruguay and Paraná meet at Punta Gorda, then funnels about 290 kilometres to the Atlantic while widening from roughly two kilometres to about 220. Some geographers call it a bay; those who call it a river crown it the world’s widest, covering about 35,000 square kilometres.
The estuary separates Argentina from Uruguay and lends its name to the Rioplatense Spanish spoken in Buenos Aires and Montevideo. River of Silver, and Argentina’s own silvery name, both trace back to legends of great silver wealth in the basin; the English plate is an archaic word for that metal. The International Hydrographic Organization draws its seaward edge from Punta del Este to Cabo San Antonio.
Barra del Indio, a submerged shoal between Montevideo and Punta Piedras, divides an inner freshwater reach, about 180 kilometres long and up to 80 wide, from an outer brackish estuary. Islands dot the upper part: Oyarvide and the Solís group on the Argentine side, and Juncal, Islote el Matón, Martín García and Timoteo Domínguez on the Uruguayan side. Heavy sediment brought down by the tributaries makes them grow over time.
Most of the fresh water comes from the Paraná, with the Uruguay and smaller streams adding the rest. Tides govern the currents and reach well upstream, affecting both feeder rivers for about 190 kilometres. The tidal range is small, but the enormous width lets the moving volume of tidewater dominate flow despite the huge river discharge. Denser seawater slides in beneath the floating fresh layer, forming a salt wedge, and the sharp salinity and density boundaries at top and bottom matter for fish breeding.
The Platine basin that feeds it covers between about 3.17 and 3.18 million square kilometres, roughly a quarter of South America, taking in south-eastern Bolivia, southern and central Brazil, all of Paraguay, most of Uruguay and northern Argentina. Only the Amazon basin is larger on the continent. Its temperate shores are home to the Uruguayan fiddler crab.
Source: Río de la Plata
