The Orinoco () is one of the longest rivers in South America at . Its drainage basin, sometimes known as the Orinoquia, covers approximately , with 65% of it in Venezuela and 35% in Colombia. It is the fourth largest river in the world by discharge volume of water ( at delta) due to the high precipitation throughout its catchment area (). The Orinoco River and its tributaries are the major transportation system for eastern and interior Venezuela and the Llanos of Colombia. The Guaviare River, with a flow of 8,200 cubic meters, is the main tributary. The environment and wildlife in the Orinoco's basin are extremely diverse.
The river's name is derived from the Warao term for "a place to paddle", derived from the terms (paddle) and (place) i.e. a navigable place.
The mouth of the Orinoco River at the Atlantic Ocean was documented by Christopher Columbus on 1 August 1498, during his third voyage. The Orinoco as well as its tributaries in the eastern Llanos, such as the Apure and Meta, were explored in the 16th century by German expeditions under Ambrosius Ehinger and his successors. In 1531, starting at the principal outlet in the delta, the Boca de Navios, Diego de Ordaz sailed up the river to the Meta. Antonio de Berrio sailed down the Casanare to the Meta, and then down the Orinoco and back to Coro. In 1595, after capturing de Berrio to obtain information while conducting an expedition to find the fabled city of El Dorado, the Englishman Sir Walter Raleigh sailed down the river, reaching the savanna country.
From April to May 1800, the Prussian-born Alexander von Humboldt and his companion, Aime Bonpland, explored stretches of the Orinoco, supported by indigenous helpers and guided by his interest to prove that South America's waterways formed an interconnected system from the Andes to the Amazon. He reported on the pink river dolphins and later published extensively on the river's flora and fauna.
The source of the Orinoco River, located at Cerro DelgadoâÂÂChalbaud (2ú19âÂÂ05â N, 63ú21âÂÂ42â W), at above sea level, was discovered in 1951 by a French-Venezuelan expedition that explored the upper Orinoco course to the Sierra Parima near the border with Brazil, headed by Venezuelan army officer Frank Risquez Iribarren.
In 1968, an expedition from The Geographical Journal set off from Manaus, Brazil aboard a SR.N6 hovercraft to follow the Rio Negro upstream to where it is joined by the Casiquiare canal, on the border between Colombia and Venezuela. After following the Casiquiare to the Orinoco River they hovered through perilous rapids of Maipures and Atures. The Orinoco was then traversed down to its mouths in the Gulf of Paria and then to the Port of Spain. The primary purpose of the expedition was filming for the BBC series The World About Us episode "The Last Great Journey on Earth from Amazon to Orinoco by Hovercraft", which aired in 1970 and demonstrated the abilities of a hovercraft, thereby promoting sales of the British invention.
The first bridge across the Orinoco River, the Angostura Bridge at Ciudad BolÃÂvar, Venezuela, was completed in 1967. The first powerline crossing of the Orinoco River was completed in 1981 for an 800kVTL single span of using two towers tall. In 1992, an overhead power line crossing for two 400kV-circuits was completed west of Morocure (between Ciudad BolÃÂvar and Ciudad Guayana). It had three towers, and the two spans measured and , respectively. In 2006, the Orinoquia Bridge was completed near Ciudad Guayana.
The course forms a wide ellipsoidal arc, surrounding the Guiana Shield; it is divided in four stretches of unequal length that very roughly correspond to the longitudinal zonation of a typical large river:
At its mouth, the Orinoco River forms a wide delta that branches off into hundreds of rivers and waterways that flow through of swampy forests. In the rainy season, the Orinoco River can swell to a breadth of and a depth of . The stream gradient of the entire river is 0.05% ( over ). Downstream of Raudales de Guaharibos the gradient is 0.01% ( over ), which is also the gradient from Ciudad Bolivar to the ocean ( over ).
Encompassing the states of Anzoategui-Guarico and Monagas states, the Interior Range forms the northern boundary and the Guayana Shield the southern boundary. Maturin forms the eastern subbasin and Guarico forms the western subbasin. The El Furrial oil field was discovered in 1978, producing from late Oligocene shallow marine sandstones in an overthrusted foreland basin.
Most of the important Venezuelan rivers are tributaries of the Orinoco, the largest being the CaronÃÂ, which joins it at Puerto Ordaz, close to the Llovizna Falls. A peculiarity of the river system is the Casiquiare canal, which starts as an arm of the Orinoco, and finds its way to the Rio Negro, a tributary of the Amazon River, thus forming a distributary and 'natural canal' between the Orinoco and the Amazon.
The boto and the giant otter inhabit the river system. The Orinoco crocodile is one of the rarest reptiles in the world; its range in the wild is restricted to the middle and lower Orinoco River basin.
More than 1,000 fish species have been recorded in the river basin, and about 15% are endemic. By far the largest orders are Characiformes and Siluriformes, which together account for more than 80% of the fresh water species. Some of the more famous are the black spot piranha and the cardinal tetra. Because the Casiquiare canal includes both blackwater and clear- to whitewater sections, only relatively adaptable species are able to pass through it between the two river systems, such as the cardinal tetra.
The river is navigable for most of its length, and dredging enables ocean ships to go as far as Ciudad BolÃÂvar, at the confluence of the CaronÃÂ River, upstream. River steamers carry cargo as far as Puerto Ayacucho and the Atures Rapids.
In 1926, a Venezuelan mining inspector found one of the richest iron ore deposits near the Orinoco delta, south of the city of San Felix on a mountain named El Florero. Full-scale mining of the ore deposits began after World War II, by a conglomerate of Venezuelan firms and US steel companies. In the early 1950s, about 10,000 tons of ore-bearing soil was mined per day.
The river deposits contain extensive tar sands in the Orinoco oil belt, which may be a source of future oil production.
Since 1973, the Civil Association Nuestros Rios son Navegables organize the Internacional Rally Nuestros Rios son Navegables, a motonautical round trip of over 1,200 kilometers through the Orinoco, Meta and Apure Rivers. Starting out from Ciudad BolÃÂvar or San Fernando de Apure, is the longest fluvial rally in the world with the participation of worldwide competitors, more than 30 support boats, logistics teams, thousands of tourists and fans travel. The boats had an average speed of 120 miles per hour.
Since 1988, the local government of Ciudad Guayana has conducted a swim race in the Orinoco and CaronÃÂ, with up to 1,000 competitors. Since 1991, the Paso a Nado Internacional de los Rios OrinocoâÂÂCaronàhas been celebrated every year in April. Worldwide, this swim meet has grown in importance, and it has a large number of competitors.
The Irish singer and songwriter Enya wrote and sang the song "Orinoco Flow", which she released in 1988. Jules Verne's novel "Superbe Orénoque" has the river as its central theme.