A drowned Ice Age canyon hides under the Uruguay
South America’s Uruguay River runs about 1,838 kilometres from Brazil’s Serra do Mar to the Río de la Plata, drawing borders with Argentina and Uruguay. Beneath today’s channel lies a submerged canyon cut when a drier Ice Age climate narrowed the stream—up to a hundred metres below the present bed.
The river begins where the Canoas and Pelotas meet about two hundred metres above sea level in Brazil’s Serra do Mar, then courses north to south as a living boundary among Brazil, Argentina, and Uruguay. Spanish ears reshaped a Guaraní name—often glossed as the river of the uru bird, among other readings. With the Paraná it builds the Río de la Plata estuary; navigation opens around Salto Chico, and the Río Negro is its chief tributary.
Unusual geology sets it apart: a drowned canyon formed when Ice Age dryness pinched the river, plunging as much as a hundred metres under today’s bottom. The basin covers about 365,000 square kilometres. Hydroelectric dams—Salto Grande downstream and Itá farther up—turn gradient into power. Five international bridges stitch the banks, from Integration and Paso de los Libres–Uruguaiana between Argentina and Brazil to Salto Grande, General Artigas, and Libertador General San Martín linking Argentina and Uruguay.
Shared water invites shared conflict. In the mid-2000s European firms ENCE and Botnia planned pulp mills at Fray Bentos opposite Argentina’s Gualeguaychú; protests from April 2005 escalated into a diplomatic crisis. Argentina took Uruguay to the International Court of Justice; hearings finished 2 October 2009, and in 2010 the court found Uruguay breached consultation duties under the 1975 river statute yet allowed the Botnia plant to keep operating. Protesters had blockaded the bridges from Entre Ríos intermittently since December 2005, and one company shifted its project 250 km south. Later in 2010 the two governments set up a joint commission for the river. The hidden canyon, one-eighth to one-third the river's width, surfaces in only two places, one being the Moconá Falls, which unusually run parallel to the channel and disappear for about 150 days a year.
Source: Uruguay River
