The full extent of the Amazon River basin The Amazon River basin covers about 7 million km², making it the largest drainage basin on Earth. It stretches across nine countries, with around 60 percent lying in Brazil and the rest spanning Peru, Colombia, Venezuela, Ecuador, Bolivia, Guyana, Suriname, and French Guiana. It drains close to 40 percent of South America through more than 1,100 tributaries, including about 17 considered major rivers. The Amazon River itself is the most voluminous in the world. On average it discharges around 200,000 cubic metres of water per second into the Atlantic Ocean. That accounts for roughly 15 to 20 percent of all the freshwater entering the world’s oceans. In flood season the river can swell to more than 40 kilometres across in places and flood vast areas of forest, creating seasonal wetlands that support enormous biodiversity. The Amazon basin contains the largest tropical rainforest on the planet. It is home to at least 10 percent of all known species, including more than 40,000 plants, over 2,000 fish, around 1,300 birds, 400 mammals, and hundreds of amphibians and reptiles, with millions of insect species still being catalogued. The rainforest acts as a critical carbon sink and plays a central role in regulating the global climate. The region is also home to more than 30 million people, including over 350 Indigenous groups, many of whom rely directly on the forest and rivers for their livelihoods and cultural traditions. Some communities remain largely uncontacted, living deep within the forest. The Amazon is often called the "lungs of the Earth" because of its immense role in producing oxygen and storing carbon. Scientists emphasise that its health is vital not only for South America but for the entire planet.