Three major river basins between the high mountains and lower plateaus dominate South America. Tributaries of the Orinoco River primarily drain the largest area of lower land in Colombia and Venezuela.

The Orinoco River of Venezuela and Colombia is one of the great rivers of the world, ranking third by discharging after the Amazon and the Congo, in South America at 2,410 km. Its drainage basin, called the Orinoquia especially in Colombia, covers 880,000 km², 76.3% in Venezuela with the rest in Colombia. The Orinoco and its Tributaries are the major transportation system for Eastern and interior Venezuela and the Llanos of Colombia. In the Orinoco basin, reverie and floodplain habitats play key roles in the conservation of biodiversity and support commercial and subsistence fisheries. The three major basins, regulate the amplitude and duration of floods, maintaining fertile Agricultural Terrain, provide habitat for numerous terrestrial and aquatic species, and support the fishery.

The Orinoco course describes a wide ellipsoidal arc, surrounding the Guiana Shield; it is divided in four stretches of unequal length that roughly correspond the longitudinal zone of a typical large river:

· Upper Orinoco, 242 km long, from its headwaters to the rapids Raudales de Guaharibos, flows through mountainous landscapes in a Northwesterly direction.

· Middle Orinoco, 750 km long, is divided into two sectors, first of which, 480 km long has a general Westward direction down to the confluence with Atabapo and Guaviare rivers at San Fernando de Atabapo. The second, flows Northward for about 270 km, along the Venezuelan Colombian border, flanking on both sides by the Westernmost Granitic up-welling 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 km long with a well developed alluvial plain, flows in a Northeastern direction, from Atures Rapids, down to Piacoa in Barrancas.

Delta Amacuro, 200 km long that empties into the Gulf of Paría and the Atlantic Ocean, a very large delta, 22.500 km² and 370 km at it's widest.