The Amazon basin has the most developed rainforest of anywhere in the world. Over two-thirds of all the fresh water on earth is found within the Amazon basin and over 20% of the earth’s oxygen is produced there. Although exact numbers are not known, the basin may contain up to one million plant species. The Amazon basin is drained by the Amazon River and its thousands of tributaries. The basin covers an area of approximately 2.5 million square miles (650 million hectares) which is approximately 40% of South America. If superimposed on the United States, it would cover nearly all of the contiguous 48 states!

The headwaters of the Amazon River are in the Andes Mountains of Peru and a mere 120 miles (190 km) from the Pacific Ocean. From there the River stretches eastward for approximately 4,000 miles (6,400 km) until if finally empties into the Atlantic Ocean at Belém in Brazil. Over this 4,000-mile length no bridge crosses the Amazon. There are approximately 1,100 tributaries that service the main river, seventeen of which are over 1,000 miles (1600 kilometers) long; the Río Negro is the most dominant tributary.

The tributaries vary in color from cloudy yellow, to clear black depending on the soil and vegetative environment of the area they are flowing from. Seasonal flooding brings soil and minerals from the mountains to the flood plains along the river, enriching the nutrient poor soil. The water level in the Amazon River can fluctuate by as much as 40 feet (12 m). The lowest levels occur in the months of August to September, and the highest levels occur in April and May. When the water is at its high point the River can be as wide as 300 miles (560 km), and at this time up to 500 billion cubic feet (14 billion m³) of water surge out to sea per day. Imagine… this is enough to sustain New York City’s fresh water supply for nine years!

The River’s deepest point occurs near the Atlantic Ocean where its depth is about 121 feet (37 m). The flow of the effluent into the Atlantic is so strong, that the waters of the Amazon River do not even begin to mix with the ocean water until the water has flowed 125 miles (230 km) into the Atlantic. This incredible force is generated purely by the sheer volume of water that flows, not by a seep gradient; indeed, the gradient from 2300 miles (3700 km) inland to where the Amazon meets the ocean would be barely enough to drain a bathtub!

Interestingly, millions of years ago the Amazon used to flow westward toward the Pacific Ocean. This was when South America, Antarctica, Africa, Australia and India were one big continent known as Gondwanaland. As the continental plates shifted, South America broke away, moved westward and collided with the Pacific Ocean plate. This collision gave rise to the Andes Mountains; subsequently the flow of the Amazon water was blocked and a vast inland lake was formed. Later geological forces caused a breach in the east, and in what must have been a cataclysmic event, the vast lake rushed into the Atlantic Ocean and as it did, created the river we now call the Amazon.

The Amazon is teeming with life. It is a birders paradise containing more species than any other ecosystem, and there are more than 4,000 species of butterflies. The lush forests of the Amazon basin are home to reptiles, amphibians, primates, tapirs, capybaras, even jaguars. The river itself contains freshwater dolphins, manatee and more than 2,000 species of fish which incidentally is more species than has been recorded for the entire Atlantic Ocean!

The climate in the Amazon is consistent with daytime temperatures ranging from the mid to upper 80’s and falling to the low 70’s in the night. Rain falls approximately 250 days of the year. While many areas have distinct rainy and dry seasons, others do not. Even the high water level is not necessarily dependent on rainfall during the rainy season, but on other factors such as the rate of evaporation and transpiration of plants. There are about 100 inches (250 centimeters) of rainfall per year in the Amazon with the forest creating about half of its own rainfall. This intricate water cycle has helped to create the diversity of life found in the Amazon basin and has sustained its existence for millions of years. It remains to be seen what devastating impact the human intervention of deforestation will have on this cycle.