Considering the Amazon accounts for around a fifth of all water discharged by rivers globally, it is unsurprising that the river system is considered to have great potential for hydroelectric power. This has given rise to 191 dams that have already been built by nine countries through which the Amazon River flows, and with 243 more in the pipeline it seems the dam building boom is showing no signs of slowing anytime soon.

But a new study has found that while these hydroelectric projects might have great “green” renewable credentials on paper, they could contribute to the extinction of “countless” species. The Amazon rainforest is home to hundreds, if not thousands, of species of animals – from fish to bats to primates – that are only found in highly localized conditions. Known as “endemic” species, sometimes they have a range of no more than a few square kilometers. As dams are built and the subsequent lagoon floods vast tracts of forest, they will destroy all the known habitat for certain animals, wiping them out forever.

The result of a dam in the Rio Candeis, which flooded hundreds of kilometers of once virgin rainforest. Joelle Hernandez/ Flickr CC BY-NC-ND 2.0

“Our research shows that an expansion of the dam network will result in huge changes to these Amazonian rivers by obstructing movement of aquatic fauna both upstream and downstream, by submerging rapids under huge lakes, by flooding adjacent forests and by creating forest islands that cannot sustain viable animal and plant populations,” explains Professor Carlos Peres from the University of East Anglia, who led the research published in Biodiversity and Conservation.

Ironically though, many of the species that could be negatively hit and even driven to extinction by the massive expansion of dam building projects in the Amazon are protected against international trade. Yet there is nothing to protect them if dams are built and their habitat is destroyed by the multitude of renewable energy projects, favored for their cheap generation of electricity.

This isn’t the first time that hydroelectricity’s “green” credential has been called into question. An earlier study showed how the building of Brazil’s largest dam, which formed a reservoir covering 2,360 square kilometers (910 square miles), dramatically reduced the number of species living there, with most of the region now completely devoid of wildlife. Not only that, but the species that do survive are often generalist or invasive species, further harming the region's biodiversity.

The 600,000-square-kilometer Sao Simao reservoir created by a hydroelectric plant in Brazil as seen from the ISS. NASA

A further knock to the green image is that dams are known to be massive net contributors to CO 2 and methane emissions, as the trees and organic matter that reservoirs cover rot down and decompose. One estimate states that in 1990 the greenhouse effect of the emissions from one dam in Brazil was actually three and half times what it would have been if the energy was sourced from oil instead. These harmful emissions are particularly pronounced in tropical regions, such as the Amazon, as the temperature favors the rapid decomposition of plants, and thus the formation of methane.

Yet countries like Brazil don’t need to go down this route. “The planned dams are not an inevitable part of Brazil’s future development because they are not necessary,” says Dr. Phillip Fearnside, one of the coauthors of the latest study. “Brazil has many better options, including investing in energy efficiency and tapping the country’s vast potential wind and solar resources. The severe impacts of Amazonian dams make pursuing other options very much in Brazil’s best interest.”

Main image: Bill Ohl/Flickr CC BY-ND 2.0