The construction of the 428 hydroelectric dams projected in the Amazon basin, which is three times more than the current number, would be devastating to the environment, according to a study published in the journal Nature.
"We must change the way we approach this issue" of dams, said Edgardo Latrubesse, a professor at the University of Texas, whose team developed an "environmental vulnerability index" of these projects.
"We are massively destroying our natural resources, we must quickly find alternatives for sustainable development", he said.
The network of tributaries of the Amazon River is the widest in the world. It feeds the main concentration of biodiversity of the planet, which would be deprived of nutrients if all these projects materialized.
Two enormous dams recently built on the Madeira River, abundant in fish, obtain, for example, an alarming score according to this index: erosion, contamination, trapped sediments ... And yet only 25 such constructions are planned for this river.
One of the most worrying impacts is the loss of downstream sediments.
"It's a big problem for densely populated deltas, which are already confronted with sea-level rise due to climate change, and they are slowly sinking all over the world."
Sludge maintenance is also essential to preserve mangroves and forests, which house many species and protect the lands and coasts of large storm-generated waves.
Previous studies have shown that changes in the circulation of sediments from the Amazon basin in the Atlantic direction will affect rainfall and storms in the region, even in the Gulf of Mexico.
The planet has more than 58,500 large dams of more than 15 meters in height or that retain more than three million cubic meters of water. 40% of them are concentrated in China, the United States and India.
"The thousands of dams built since the mid-nineteenth century completely changed the plumbing of our planet," said James Syvitski, a specialist in earth's surface evolution at the University of Colorado.
The most modern dams manage to minimize the impacts on the fauna or better manage the sediments that gradually fill the reservoirs and end up rendering them ineffective.
"But these measures cost money and reduce the profitability of investment," according to Syvitski.