Water Systems

At 6,400 kilometers, or 4,000 miles, in length, the Amazon River is the second longest river in the world. The fresh water flows through it and into the ocean at an astonishing rate of 209,000 cubic meters per second—more than the next six largest rivers combined. The width of the river extends anywhere between 4 and 50 kilometers, reaching its maximum width during the wet season when increased rainfall swells the river and floods the banks. As the largest watershed in the world, the Amazon River supplies anywhere from 9 to 30 million gallons of freshwater to the Atlantic Ocean each day. This water is then swept around the world on ocean currents.

A majority of the water in the Amazonia Rivers is attributed to glacial melt from the Andes in the western Amazon and the rains created by the Amazon’s trees. The mighty river begins in the Andes flowing from West to East, eventually reaching a drainage basin of over 7,000,000 square kilometers—nearly 40% of South America.

The Amazon basin contains the largest share of freshwater species in the world due to the immense size of the basin and the variety of aquatic habitat. Freshwater species in the Amazon most commonly include fish, crustaceans, mollusks and insect larvae and are food sources for a number of aquatic animals. Freshwater fish are also eaten by land-dwelling salamanders, mammals and birds. There are at least 3,000 species of freshwater fish species in the Amazon River basin. Though the inhabitants of the Amazon River are numerous and diverse, there is limited information on Amazonian aquatic species due to the difficulty of studying such an extensive river system.

The Amazon also provides essential ecosystem services such as the transport of nutrients and sediment. It also provides services for humans, such as water for agriculture, power generated by hydroelectric plants, transportation, and food.

The Orinoco River flows north of the Amazon. The Orinoco flows in a giant arc for more than 2,736 kilometers (1,700 miles), originating in the Guiana Highlands of northern Brazil and discharging in the Atlantic Ocean in Venezuela. The Orinoco River basin covers an area of about 948,000 square kilometers (366,000 square miles) and encompasses approximately 80 percent of Venezuela and 25 percent of Colombia.

A vast savanna or grassland region, known as the Llanos, is the primary biome of the Orinoco River basin. The Llanos is primarily made up of grasses. Swamp grasses, sedges, and bunchgrass are found in wet, low-lying areas. Carpet grass is found in the higher and drier elevations. Like most grassland biomes, the Llanos is the perfect habitat for many bird species, including the scarlet ibis, bellbird, and umbrellabird. Important river species include the piranha, electric eel, and the Orinoco crocodile, which can reach a length of more than 6 meters (20 feet).

Compared to many of the world’s river systems, the Orinoco is relatively intact. This may not last for long as the river and its surrounding areas are threatened by pollution and mining activities. Large areas of the flooded forests have been cleared for agriculture and cattle ranching. And large dams planned for several major tributaries will destroy water flows that support the region’s unique aquatic life.