When Andrés Ruzo was just a small boy, his grandfather in Peru told him a story with an odd detail: There is a river, deep in the Amazon, that boils. Years later, he resolved to find it — and find out what’s going on — and headed to the jungle.

On a typical sunny day in the Amazon, 20 billion metric tons of water pass through the trees and into the air. This is more than just a feat of Nature — it’s at the heart of South America’s economy, as researcher Antonio Donato Nobre explains.