The Orinoco region is a geographical territory stretching from the Colombian Andes to almost all the territory of Venezuela. Located north of the Amazon rainforest, it is a territory mostly flat or slightly wavy composed of intertropical vast savannas and gallery forests along rivers.
The Orinoco region, called localy as Orinoquía, is also the Orinoco River basin, one of the largest water basins in the world which has many large rivers that drain into the Orinoco along its entire length, and covers 880,000 square kilometers, 23.7% in Colombia and rest in Venezuela. The Orinoco River is the fourth largest river in the world and the second in America after the Amazon River with an average flow of 30,000 cubic meters per second. Its length is 2410 km (1497.5 miles) and its basin covers 880,000 square kilometers, 23.7% in Colombia and the rest in Venezuela.
The Orinoco river is born in the Delgado Chalbaud hill in the Parima mountains, located on the border between Venezuela and Brazil. Its course draws a great arc towards the northwest, then goes west to the geographical zone that Alexander von Humboldt called ‘Estrella Fluvial del Sur’ (The southern river star), which is the triple confluence of the Orinoco with the Guaviare and the Atabapo rivers. Then the Orinoco travels north along the border between Venezuela and Colombia, to the confluence with the Meta river, and from there it runs into Venezuelan territory again, covering a total of 2140 kilometers to its mouth forming an immense delta in the Atlantic Ocean.
The first hand-drawn map of the Orinoco is from an expedition of 1732 that has very precise details of its tributaries. This map is drawn with the north down.
Curiously, the Casiquiare river forms a natural channel between the Orinoco and Amazon river. It starts as an arm of the Orinoco but ends up flowing into the Black River that is a tributary of the Amazon, so that is why many species of fish have found a way to populate the two basins, as is the case of the Speckled Peacock Bass (Cichla temensis) who is originally from the Orinoco region but is located in the Black River in Brazil too.
Most of the large rivers that drain into the Orinoco come from the Colombian Andes or the plains of Los Llanos in Colombia. The first flowing in is the Guaviare River that provides most of Orinoco’s flow from that point of confluence. Years ago the headwaters of the Orinoco were widely discussed as some experts insisted that its origin occurs in the Andes of Colombia because if that point is taken as the source, in other words that the Guaviare river is the Orinoco river before flowing into the ‘Estrella Fluvial del Sur’, it's length is much greater than if it was born in the Casiquiare, but finally the theory that explains the Orinoco born in the Casiquiare prevailed due to the similarity of all the territory the Orinoco flows. To the North, from Colombia, also many rivers flow into the Orinoco, such us the Guaviare (which brings the waters of the Inírida River), Mataveni, Vichada, Tuparro, Tomo, Dagua, Vita and Meta rivers.
The Orinoco region has an independent climate regime of the Andes and the Amazon. The rainy season goes from mid-April to early December.
During this time the rivers overflow in the plains creating an ideal environment for many species of fish to reproduce and their offspring are strengthened in temporary pools and amidst the trees of the gallery forest environment, where they will have many more sources of food and shelter from predators that are usually in rivers.
The dry season runs from December to mid-April, and that lack of rain causes rivers return to their usual channel at the end of December. From January the waters decrease drastically, reaching 14.5 meters below the peak. This is the fishing season in the Orinoco because the fish are found in rivers and the lagoons near them.
The Lagoons and Oxbow Lakes
Orinoco basin rivers have many lagoons that are connected to their banks or are relatively close to them. This is because geologically speaking the soil of the region is mostly sandy, and geographically there is no presence of mountains that force the rivers to channel in a definitive way. Throughout the centuries because of the erosion caused by water on the banks, the rivers have made their way through different routes and have ended up generating oxbow lakes (with no current because they are only connected by one mouth), this is known locally as lagoons.
By their origin, most of these gaps are the same width of the river with a length ranging from 500 meters to several kilometers, although we can find lagoons, with the same origin, which are very broad, covering several acres.
The Gallery Forest
All of the Orinoco rivers are surrounded by a forest along its entire length that makes a difference with the intertropical zone savannah. These forests may have a width of up to one kilometer depending on the soil and topography. Trees and shrubs are concentrated there, they have done so because they get water from rivers and streams throughout the year. The species of trees of this gallery forest are exclusive of the region.
During the dry season, the gallery forests and these rivers are the gathering scenario of birds such as eagles, herons, storks, local wild turkeys, ducks and many other species. There also converge all mammals, reptiles and amphibians of the plains in search of food and water as the plain dries and they can't find there any food source. This makes the fishing season in the rivers of the Orinoco basin the best time of the year to observe and interact with the wildlife of the plains.