I.

Introduction

Amazon (Portuguese and Spanish, Amazonas), river, northern South America, largely in Brazil, ranked as the largest in the world in terms of catchment area, number of tributaries, and volume of water discharged. Measuring about 6,400 km (4,000 mi) from source to mouth, it is second in length only to the Nile among the rivers of the world. With its hundreds of tributaries, the Amazon drains a territory of more than 6 million sq km (2.3 million sq mi)—more than twice the size of the region drained by the Nile. Roughly half of the area drained is in Brazil; the rest is in Peru, Ecuador, Bolivia, and Venezuela. It is estimated that the Amazon discharges between 34 and 121 million litres (7.5 and 27 million gallons) of water per second and deposits a daily average of 3 million tons of sediment near its mouth. The annual outflow from the river accounts for one-fifth of all the fresh water that drains into the oceans of the world. The outpouring of water and sediment is so vast that the salinity and colour of the Atlantic Ocean are altered for a distance of about 320 km (200 mi) from the mouth of the river.