Most areas in the Amazon River Basin have a tropical rainforest climate, while the upper reaches have a plateau mountain climate with an annual rainfall of more than 2,000 mm. The fertile silt deposited by the Amazon River nourishes an area of ​​6.5 million square kilometers, and the famous Amazon rainforest grows in the Amazon River Basin. It is also the largest plain in the world (with an area of ​​5.6 million square kilometers).

The plain is low and flat, most of which is below 150 meters above sea level, so there are winding rivers and many lakes. Rainy, humid and continuously high temperatures are its significant climatic characteristics.

Due to the rainy areas near the equator, the Amazon has abundant water all year round. The average annual flow at the mouth of the Amazon River is 220,000 cubic meters per second, making it the river with the widest basin and the largest flow in the world. Brazilians proudly call it the "River Sea". It is estimated that about 20-25% of all the water flowing on the earth's surface is in the Amazon River.