The Amazon River (US /ˈæməzɒn/ or UK /ˈæməzən/; Spanish and Portuguese: Amazonas) in South America is the largest river by discharge of water in the world, and the second in length.
Although the Amazon's most distant source has been accepted for nearly a century as the headwaters of the Apurímac river on Nevado Mismi, a 2014 study indicates that the Amazon's most distant source is on the Cordillera Rumi Cruz at the headwaters of the Mantaro river in Peru. The Mantaro and Apurímac confluence, and with other tributaries form the Ucayali, which in turn confluences with the River Marañón upstream of Iquitos, Peru, to form what countries other than Brazil consider to be the main stem of the Amazon. For Brazil this section of the river is the Solimões until it confluences with the Rio Negro at the Meeting of Waters (Portuguese: Encontro das Águas) at Manaus, the river's largest city.
The Amazon averages a discharge of about 209,000 cubic metres per second (7,400,000 cu ft/s; 209,000,000 L/s; 55,000,000 USgal/s) — approximately 6,591 cubic kilometres per annum (1,581 cu mi/a) — which is greater than the next seven largest independent rivers combined. The Amazon basin is the largest drainage basin in the world, with an area of approximately 7,050,000 square kilometres (2,720,000 sq mi), and accounts for roughly one-fifth of the world's total river flow. The portion of the river's drainage basin in Brazil alone is larger than any other river's basin. The Amazon enters Brazil with only one-fifth of the flow it finally discharges into the Atlantic Ocean, yet already has a greater flow at this point than the discharge of any other river.
The river enters the Atlantic Ocean in north-eastern Brazil in a broad estuary about 240 kilometres (150 mi) wide. The mouth of the main stem is 80 kilometres (50 mi). The width of the Amazon is between 1.6 and 10 kilometres (1.0 and 6.2 mi) at low stage, but expands during the wet season to 48 kilometres (30 mi) or more. Because of its vast dimensions, it is sometimes called "The River Sea".