The Orinoco River has the third largest flow of the world’s rivers averaging a discharge of 5.4 x 1011 m3 per year to the Atlantic Ocean. Combined, the Orinoco and Amazon Rivers account for 25 percent of the freshwater discharge to the world’s oceans.
The Orinoco River originates in the Sierra Parima at an elevation of 1,074 m and receives water from more than 2,000 tributaries along its 2,500 km length. The drainage basin of the Orinoco River is the third largest in South America with an area of 830,000 km2. About 77 percent of the drainage basin is in Venezuela, the remainder being in Colombia and Brazil.
The Orinoco River is characterized by a series of rapids between which the river flows in alluvial channels. Where the river reaches the delta, distributaries fan across the southern part of the delta from an apex at Barrancas. Average discharge to the Delta del Orinoco is 36,000 m3 s-1. Discharge is variable, with monthly mean discharges ranging from 1,330 to 81,000 m3 s-1. During the high-water season, the lower delta is almost completely flooded.
Two types of streams are found in the delta: brown-water streams (which are directly connected to upland rivers and carry suspended sediment) and black-water streams (which drain delta swamps and carry clear water rich in humic acids).