The river measures about 1,838 kilometres (1,142 mi) in length and starts in the Serra do Mar in Brazil, where the Canoas River and the Pelotas River are joined, at about 200 m above mean sea level. In this stage the river goes through uneven, broken terrain, forming rapids and falls. Its course through Rio Grande do Sul is not navigable.
Unusual feature of Uruguay River is a submerged canyon along most of its length. This canyon has formed in dry period during the Ice Age and its depth in some locations reaches 100 m. Canyon is visible only at Moconá Falls - unusual, up to 12 m high and more than 2 km wide waterfall, which has formed on a rim of this canyon 1 215 km from the mouth of Uruguay.
Together with the Paraná River, the Uruguay forms the Río de la Plata estuary. It is navigable from around Salto Chico. Its main tributary is the Río Negro, which is born in the south of Brazil and goes through Uruguay 500 km until its confluence with the Uruguay river, which is located 100 km north from the Uruguay's confluence with the Río de la Plata, in Punta Gorda (Colonia Department, Uruguay).
The river is crossed by five international bridges called (from north to south): Integration Bridge and Paso de los Libres-Uruguaiana International Bridge, between Argentina and Brazil; and the Salto Grande Bridge, General Artigas Bridge and Libertador General San Martín Bridge between Argentina and Uruguay.
The chief rivers of Argentina are the Parana, which traverses the north central portion of the country; the Uruguay, which forms part of the boundary with Uruguay; the Paraguay, which is the main affluent of the Parana; and the Rio de la Plata, the great estuary formed by the confluence of the Parana and the Uruguay rivers. The Parana-Uruguay system is navigable for about 3,000 km (about 2,000 mi). A famed scenic attraction, the Iguacu Falls, is on the Iguacu River, a tributary of the Parana. Other important rivers of Argentina are the Rio Colorado, the Rio Salado, and the Rio Negro. In the area between the Rio Salado and the Rio Colorado and in the Chaco region, some large rivers empty into swamps and marshes or disappear into sinks. The hydrography of the country includes numerous lakes, particularly among the foothills of the Patagonian Andes. The best known are those in the alpine lake country around the resort town of San Carlos de Bariloche (Bariloche).