Orinoco

Orinoco, river, Venezuela, one of South America's longest rivers, extending about 2,560 km (1,591 mi). Its source is in the Guiana Highlands, on the slopes of the Parima Mountains, in extreme south-eastern Venezuela, on the border of Brazil. It flows north-west to a point near La Esmeralda, where the Canal Casaquiare goes south and after a course of 290 km (180 mi) enters the Negro, a tributary of the Amazon River. The main branch continues north-west to the town of San Fernando de Atabapo, where it receives the Guaviare River and, flowing generally north, forms the border between Venezuela and Colombia. After passing over the Maipures and Atures rapids and receiving the Meta River from the west, it meets the Apure River. The Orinoco River then turns north-east and traverses the Llanos, or plains, of Venezuela before emptying into the Atlantic Ocean. Cataracts separate different sections of the river.

The Orinoco, which averages 6 km (4 mi) in width, is augmented from the south by several rivers, including the Caura and the Caroni. The delta of the river, with an area of about 20,700 sq km (8,000 sq mi), begins about 190 km (120 mi) from the Atlantic. The total area of the drainage basin is approximately 1,165,500 sq km (about 450,000 sq mi); its average discharge is about 30 million litres (6.6 million gallons) per second, the majority of this deriving ultimately from melting snow. The Orinoco is navigable for ocean-going ships for some 420 km (260 mi), from the mouth to the city of Ciudad Bolívar, the major commercial and communications centre for the drainage basin. It is navigable for smaller craft for a distance of about 1,600 km (1,000 mi).

The Orinoco was sighted by Christopher Columbus in 1498 and was first explored by Europeans to the confluence with the Meta River in 1530-1531. In 1616 an expedition under Sir Walter Raleigh penetrated the river in an attempt to found a gold-mining enterprise, but was repulsed by the Spanish. The German naturalist Alexander von Humboldt explored the upper reaches in 1799. An expedition led by the American doctor and explorer Herbert Spencer Dickey claimed to have reached its headwaters in 1931. Several Brazilian and Venezuelan expeditions in 1944 and in the 1950s penetrated further to the site that is now accepted as the headwaters. Some portions of the river remain relatively unexplored, particularly the upper reaches.