© iStockPhoto / Birgit Prentner
The Orinoco Basin, extending from the Andes and the plains of the Llanos and the Guiana shield of Colombia and Venezuela to the Atlantic, covers 980,000km2. The river flows 2,140km from its source in the extreme south of the Guianan massif until reaching the ocean.
The “Oriniquia” as it’s known locally, represents one of the most biologically and hydrologically diverse areas of the world. At over 33,000 m3/sec, it ranks fourth worldwide in average discharge.
The Orinoco through the seasons
The Orinoco changes greatly from season to season.
Between May and August, rainfall oscillating between 5,000 and 7,000mm and the relatively flat topographic conditions of the basin generate a flooded area covering almost 10% of the basin. This creates new habitats and resources for many aquatic species.
In Ciudad Bolivar (the capital of the eastern Venezuelan state of Bolivar), the annual variation in water level ranges from 15m to 18m and the discharge rate varies from one season to the next.
A tributary of the Orinoco River called the Casiquiare connects with the Rio Negro, a tributary of the Amazon River, forming a 'natural canal' between the Orinoco and the Amazon River.
A geological history along the Orinoco River
The Orinoco River runs through two distinct geological areas: one is the oldest geological formation on the continent, to the south of the river, and the other is a relatively recent formation of land, created by sediment washed down from the Andes.
Over time, the eroding action of the river has contributed to the isolation of an area of high sandstone mesas, locally known as the tepuis, some with an altitude of 1,500m. One of these is home to Angel Falls, which at nearly 1,000m is the highest free-falling waterfall on Earth.
 Kricher, 1997