Orinoquia Bridge near Ciudad Guayana, Venezuela
Orinoco's drainage basin
|- location||Cerro Delgado-Chalbaud, Parima Mountains, Venezuela|
|- elevation||1,047 m (3,435 ft)|
|Atlantic Ocean, Venezuela|
ORINOCO Latitude and Longitude:
|0 m (0 ft)|
|Length||2,140 km (1,330 mi)|
|Basin size||880,000 km2 (340,000 sq mi)|
|- average||37,000 m3/s (1,300,000 cu ft/s)|
|- minimum||21,000 m3/s (740,000 cu ft/s)|
|- maximum||54,000 m3/s (1,900,000 cu ft/s)|
The Orinoco River (Spanish pronunciation: [oɾiˈnoko]) is one of the longest rivers in South America at 2,140 kilometres (1,330 mi). Its drainage basin, sometimes known as the Orinoquia,[ citation needed] covers 880,000 square kilometres (340,000 sq mi), with 76.3 percent of it in Venezuela and the remainder in Colombia. It is the fourth largest river in the world by discharge volume of water. The Orinoco River and its tributaries are the major transportation system for eastern and interior Venezuela and the llanos of Colombia. The environment in the Orinoco's basin is extremely diverse; it hosts a wide variety of flora and fauna.
The mouth of the Orinoco River at the Atlantic Ocean was documented by Columbus on 1 August 1498, during his third voyage. Its source at the Cerro Delgado–Chalbaud, in the Parima range, was not explored until 1951, 453 years later. The source, near the Venezuelan– Brazilian border, at 1,047 metres (3,435 ft) above sea level ( ), was explored in 1951 by a joint Venezuelan–French team.
The Orinoco Delta, and 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 Diego de Ordaz, starting at the principal outlet in the delta, the Boca de Navios, sailed up the river to the Meta. Antonio de Berrio sailed down the Casanare to the Meta, and then down the Orinoco River 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 savannah country.
The first bridge across the Orinoco River was the Angostura Bridge at Ciudad Bolívar, Venezuela, completed in 1967.  In 2006 a second bridge was completed near Ciudad Guayana, Venezuela, known as the Orinoquia Bridge.[ citation needed]
The first powerline crossing of the Orinoco River was completed in 1981 for an 800 kV TL single span of 1,200 metres (3,900 ft) using two towers 110 metres (360 ft) tall.  In 1992, an overhead power line crossing for two 400 kV-circuits was completed just west of Morocure (between the cities of Ciudad Bolivar and Ciudad Guayana), north of the confluence of Routes 1 and 19. It had three towers, and the two spans measured 2,161 metres (7,090 ft) and 2,537 metres (8,323 ft), respectively.    
The course of the Orinoco forms a wide ellipsoidal arc, surrounding the Guiana Shield; it is divided in four stretches of unequal length that roughly correspond to the longitudinal zonation of a typical large river:
- Upper Orinoco — 242 kilometres (150 mi) long, from its headwaters to the rapids Raudales de Guaharibos, flows through mountainous landscape in a northwesterly direction
- Middle Orinoco — 750 kilometres (470 mi) long, divided into two sectors, the first of which ca. 480 kilometres (300 mi) long has a general westward direction down to the confluence with the Atabapo and Guaviare rivers at San Fernando de Atabapo; the second flows northward, for about 270 kilometres (170 mi), along the Venezuelan - Colombian border, flanked on both sides by the westernmost granitic upwellings of the Guiana Shield which impede the development of a flood plain, to the Atures rapids near the confluence with the Meta River at Puerto Carreño
- Lower Orinoco — 959 kilometres (596 mi) long with a well-developed alluvial plain, flows in a northeast direction, from Atures rapids down to Piacoa in front of Barrancas
- Delta Amacuro — 200 kilometres (120 mi) long that empties into the Gulf of Paría and the Atlantic Ocean, a very large delta, some 22,500 km2 (8,700 sq mi) and 370 kilometres (230 mi) at its widest.
At its mouth, the Orinoco River forms a wide delta that branches off into hundreds of rivers and waterways that flow through 41,000 km2 (16,000 sq mi) of swampy forests. In the rainy season, the Orinoco River can swell to a breadth of 22 kilometres (14 mi) and a depth of 100 metres (330 ft).
Most of the important Venezuelan rivers are tributaries of the Orinoco River, the largest being the Caroní, which joins it at Puerto Ordaz, close to the Llovizna Falls. A peculiarity of the Orinoco 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, thus forming a 'natural canal' between Orinoco and Amazon.
- Apure: from Venezuela through the east into the Orinoco
- Arauca: from Colombia to Venezuela east into the Orinoco
- Atabapo: from the Guiana Highlands of Venezuela north into the Orinoco
- Caroní: from the Guiana Highlands of Venezuela north into the Orinoco
- Casiquiare canal: in SE Venezuela, a distributary from the Orinoco flowing west to the Negro River, a major affluent to the Amazon
- Caura: from eastern Venezuela (Guiana Highlands) north into the Orinoco
- Guaviare: from Colombia east into the Orinoco
- Inírida: from Colombia southeast into the Guaviare.
- Meta: from Colombia, border with Venezuela east into the Orinoco
- Ventuari: from eastern Venezuela (the Guiana Highlands) southwest into the Orinoco
- Vichada: from Colombia east into the Orinoco
The boto and the giant otter inhabit the Orinoco 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 1000 fish species have been recorded in the river basin and about 15% are endemic.  Among the fish in the river are species found in brackish or salt water in the Orinoco estuary, but also many restricted to fresh water. 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. The latter species, which is important in the aquarium industry, is also found in the Rio Negro, revealing the connection between this river and the Orinoco through the Casiquiare canal.  Because the Casiquiare includes both blackwater and clear- to whitewater sections, only relatively adaptable species are able to pass through it between the two river systems. 
The river is navigable for most of its length, and dredging enables ocean ships to go as far as Ciudad Bolívar, at the confluence of the Caroní River, 435 kilometres (270 mi) 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. At the start in the early 1950s, about 10,000 tons of ore-bearing soil was mined per day. 
Encompassing the states of Anzoategui- Guarico and Monagas states, the Interior Range forms the northern boundary and the Guayana Shield the southern boundary. :155 Maturin forms the eastern subbasin and Guarico forms the western subbasin. :156 The El Furrial oil field was discovered in 1978, producing from late Oligocene shallow marine sandstones in an overthrusted foreland basin. :155
Since 1988, the local government of Ciudad Guayana has conducted a swim race in the rivers Orinoco and Caroní, with up to 1,000 competitors. Since 1991, the Paso a Nado Internacional de los Rios Orinoco–Caroní has been celebrated every year, on a Sunday close to 19 April. Worldwide, this swim-meet has grown in importance, and it has a large number of competitors.  The 26th meet was held in 2016. 
- Orinoco River at GEOnet Names Server
- Helferich, Gerard (2004) Humboldt's Cosmos: Alexander von Humboldt and the Latin American Journey that Changed the Way We See the World, Gotham Books, New York, ISBN 1-59240-052-3.
- Scott, R. (2001). In the Wake of Tacoma: Suspension Bridges and the Quest for Aerodynamic Stability. American Society of Civil Engineers. p. 184. ISBN 9780784470732. Retrieved 2015-04-13.
- "Experience". SAE Power Lines.
- "Critical Path" (PDF). PEI. June 2005. pp. 105–111, page 107. Archived from the original (PDF) on 23 September 2006.
- "Pylons of the Orinoco High-Voltage Crossing". International Database for Civil and Structural Engineering. Archived from the original on 13 October 2015.
- "Orinoco Powerline Crossing". Skyscraper Source Media Inc. Archived from the original on 13 October 2015.
- "Ciudad Guayana, Venezuela : Image of the Day". earthobservatory.nasa.gov. 2006-01-23. Retrieved 2009-10-31.
- WWF: Orinoco River Basin, South America. Retrieved 24 May 2014
- Thorbjarnarson, John B.; Hernández, Gustavo (1993). "Reproductive ecology of the Orinoco crocodile (Crocodylus intermedius) in Venezuela. I. Nesting ecology and egg and clutch relationships". Journal of Herpetology. 27 (4): 363–370. doi: 10.2307/1564821. JSTOR 1564821.
- Reis, R.E.; J.S. Albert; F. Di Dario; M.M. Mincarone; P. Petry; and L.A. Rocha (2016). Fish biodiversity and conservation in South America. Journal of Fish Biology 89(1): 12–47.
- Hales, J., and P. Petry: Orinoco Llanos. Orinoco Delta & Coastal Drainages. Retrieved 24 May 2014.
- Seriously Fish: Paracheirodon axelrodi, Cardinal Tetra. Retrieved 24 May 2014
- Staeck, W.; Schindler, I. (2015). "Description of a new Heros species (Teleostei, Cichlidae) from the Rio Orinoco drainage and notes on Heros severus Heckel, 1840" (PDF). Bulletin of Fish Biology. 15 (1–2): 121–136.
- "Venezuela's Magnetic Mountain" Popular Mechanics, July 1949
- Forero, Juan (1 June 2006). "For Venezuela, A Treasure In Oil Sludge". The New York Times. 155 (53597). pp. C1–C6. Archived from the original on 12 December 2016.
- Prieto, R., Valdes, G., 1992, El Furrial Oil Field, In Giant Oil and Gas Fields of the Decade, 1978-1988, AAPG Memoir 54, Halbouty, M.T., editor, Tulsa: American Association of Petroleum Geologists, ISBN 0891813330
- "Antecedentes y Sumario Paso a Nado Internacional de Los Rios Orinoco/Caroni" Paso Nado Internacional de Los Rios Orinoco y Caroní" [Antecedents and Summary of the International Swim Meet of the Orinoco and Caroni Rivers] (in Spanish). Archived from the original on 17 December 2007.
- "26 edición Paso a Nado de Ríos Orinoco y Caroní 2016". Roberto Muñoz Natación Venezuela. Archived from the original on 9 November 2016.
- Stark, James H. 1897. Stark's Guide-Book and History of Trinidad including Tobago, Granada, and St. Vincent; also a trip up the Orinoco and a description of the great Venezuelan Pitch Lake. Boston, James H. Stark, publisher; London, Sampson Low, Marston & Company. (This book has an excellent description of a trip up the Orinoco as far as Ciudad Bolívar and a detailed description of the Venezuelan Pitch Lake situated on the western side of the Gulf of Paria opposite.)
- MacKee, E.D., Nordin, C.F. and D. Perez-Hernandez (1998). "The Waters and Sediments of the Rio Orinoco and its major Tributaries, Venezuela and Colombia." United States Geological Survey water-supply paper, ISSN 0886-9308 /A-B. Washington: United States Government Printing Office.
- Weibezahn, F.H., Haymara, A. and M.W. Lewis (1990). The Orinoco River as an ecosystem. Caracas: Universidad Simon Bolivar.
- Rawlins, C.B. (1999). The Orinoco River. New York: Franklin Watts.
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