The Amazon River is the largest river on Earth by volume, discharging roughly 6,900 cubic kilometers of freshwater into the Atlantic Ocean every year. That single river accounts for about one-sixth of all the freshwater that flows from land to sea worldwide. Its importance stretches far beyond South America, influencing global climate, supporting unmatched biodiversity, and sustaining millions of people who depend on it for food, water, and transportation.
One-Sixth of Earth’s Freshwater Discharge
The Amazon’s sheer scale is difficult to overstate. At its mouth, the river pushes out an average of 220,000 cubic meters of water per second. For context, roughly 41,000 cubic kilometers of freshwater return to the sea from all the world’s rivers combined each year, and the Amazon alone contributes about 6,900 of those. No other river comes close. The Congo, the second-largest by discharge, moves less than a third of that volume.
This massive outflow shapes ocean conditions hundreds of kilometers offshore. The freshwater plume lowers salinity, changes surface temperatures, and influences ocean currents in the tropical Atlantic. It also carries roughly 754 million tons of sediment into the ocean annually. About 20 percent of that sediment forms fluid mud and migrating mud banks along a 1,500-kilometer coastal belt stretching from the river’s mouth northward to the Orinoco River, physically reshaping the coastline of northeastern South America.
The Most Biodiverse River System on Earth
The Amazon basin contains more freshwater species than any other river system. A comprehensive database spanning nearly 200 years of scientific records documents at least 2,406 valid native freshwater fish species in the basin. New species are still being described regularly. For comparison, all of Europe’s rivers combined hold a few hundred fish species. The Amazon’s fish alone outnumber those of entire continents.
Beyond fish, the river system supports river dolphins, giant otters, caimans, anacondas, manatees, and thousands of invertebrate species. Floodplain forests that the river inundates seasonally create unique habitats where fish swim among tree trunks and feed on fallen fruit, linking aquatic and terrestrial ecosystems in ways found almost nowhere else. Many of these species are endemic, meaning they exist only in the Amazon basin.
Driving Rainfall Across South America
The Amazon doesn’t just carry water to the ocean. The surrounding rainforest recycles enormous quantities of moisture back into the atmosphere through evapotranspiration, where trees pull water from the soil and release it as vapor through their leaves. This process generates what scientists sometimes call “flying rivers,” streams of atmospheric moisture that travel westward and southward across the continent.
The numbers are striking. Roughly 40 percent of annual rainfall over the eastern foothills of the Andes originates as moisture evaporated from the Amazon basin. Nearly 30 percent of rainfall over northern Argentina comes from similar recycling processes. These regions include some of South America’s most productive agricultural land, growing soybeans, corn, and cattle forage. Without the Amazon’s moisture pump, rainfall in these areas would drop significantly, threatening food production for the continent and global commodity markets.
A Massive Carbon Reserve
The Amazon basin stores an estimated 650 billion tons of carbon dioxide in its trees. That figure represents one of the largest terrestrial carbon reserves on the planet. As long as the forest stands, that carbon stays locked away. When trees are burned or die from drought, the carbon enters the atmosphere and accelerates warming.
This storage function makes the Amazon a critical piece of global climate stability. Deforestation and degradation don’t just destroy habitat locally. They release carbon that affects temperatures worldwide, creating feedback loops where warming leads to more drought, which kills more trees, which releases more carbon.
Food and Livelihood for Millions
For communities along the Amazon and its tributaries, the river is the primary source of protein. In traditional villages along the Rio Madeira, one of the Amazon’s major tributaries, average fish consumption reaches about 148 kilograms per person per year. That’s roughly ten times the global average for fish consumption. Some residents eat fish as many as 14 times per week. For these populations, the river isn’t a scenic feature. It’s the food system.
The river also serves as the main transportation network across a region where roads are scarce or nonexistent. Communities rely on boat travel for everything from commuting to school to shipping goods to market. Cities like Manaus and Belém function as inland ports, connecting remote populations to broader economic networks. Brazil has also pursued large-scale hydroelectric development in the basin, with plans for dozens of major dams across tributaries like the Tapajós, where 43 large dams (each over 30 megawatts) have been proposed.
What Happens When the River Weakens
Recent years have shown what’s at stake when the Amazon’s water cycle breaks down. In the fall of 2023, an unprecedented drought and heat wave dropped the river to its lowest levels ever recorded. Water temperatures in some areas reached 41°C (106°F), a reading so extreme that researchers who had spent careers measuring tropical waters called it shocking. In Lake Tefé, that temperature was uniform from surface to bottom at six feet deep, essentially cooking the ecosystem.
Hundreds of river dolphins died from overheating in lakes left behind by the shrinking river. Researchers from a nearby institute scrambled to capture surviving dolphins and relocate them to cooler waters, but the scale of the die-off was devastating. The 2023 drought wasn’t an isolated event. Climate data shows the Amazon is experiencing more frequent and more intense droughts and floods, a pattern tied directly to rising global temperatures and deforestation.
These extremes ripple outward. Low water levels strand cargo vessels and cut off isolated communities. Drought weakens the forest’s ability to recycle moisture, reducing rainfall in agricultural regions thousands of kilometers away. Fish populations crash, removing the main protein source for riverside communities. The Amazon’s importance becomes most visible precisely when it starts to fail.