The Amazon River begins its journey high in the Andes Mountains of Peru. It is recognized as the world’s largest river based on the volume of water it moves. The Amazon accounts for approximately one-fifth of all fresh water discharged by rivers globally. Stretching over 4,000 miles, it is one of the two longest waterways on Earth.
The Final Destination: The Atlantic Ocean
The powerful current of the Amazon River completes its traverse across the South American continent by emptying into the Atlantic Ocean. This discharge occurs along the northeastern coast of Brazil, just south of the equator. The sheer momentum and volume of the river’s output mean the transition is not a simple merging of water masses.
The river mouth is located in the Brazilian state of Pará, representing the end point for the planet’s largest drainage basin. Before the freshwater fully dissipates into the saltwater, a zone of mixing begins far from the actual coastline. Here, the river’s brown, sediment-laden waters first encounter the Atlantic.
Geography of the River Mouth
The Amazon does not terminate in a single, narrow estuary like many other major rivers, but instead forms a vast and complex delta system. This expansive mouth is characterized by numerous islands and channels that distribute the river’s flow before it reaches the open ocean. The complexity begins with Marajó Island, which is positioned directly in the path of the flow.
Marajó Island is the world’s largest fluvial island, meaning it is entirely surrounded by river or ocean waters. The island covers approximately 15,500 square miles, significantly shaping the river’s final path. The main body of the Amazon’s water flows north of Marajó Island through two primary channels.
A smaller portion of the water flows south of the island, connecting with the Pará River estuary via a network of narrow channels called furos. This southern outlet also receives water from the Tocantins River. The resulting maze of waterways and islands creates a mouth that spans hundreds of miles across.
The Vast Freshwater Plume
The volume of water released by the Amazon, averaging around 209,000 cubic meters every second, creates the Amazon River Plume. This plume is a tongue of low-salinity water that extends far into the Atlantic Ocean. The scale of the freshwater discharge is so great that its effects can be observed from space.
The plume significantly reduces the surface salinity of the ocean, sometimes by three to eight practical salinity units (PSU). This desalinated layer of river water, typically only 3 to 15 meters thick, floats atop the denser, saltier ocean water. The plume can extend hundreds of miles offshore, with its influence traceable up to 4,000 kilometers away.
Once it enters the ocean, the plume is quickly carried northwestward along the coast by the North Brazil Current. This movement transports the Amazon’s water, along with its load of dissolved nutrients and sediment, towards the Caribbean Sea. The influx of nutrients fertilizes the ocean surface, promoting the growth of microscopic marine plants and influencing the local marine ecosystem.