Hydroelectric Dams Planned For World's Largest Rivers Threaten Fish

Hydroelectric dam builders, and the need to curb greenhouse emissions, often underestimate the long-term effects these massive structures have on local biodiversity. In a new study, 30 leading aquatic ecologists warn impending dams in the Mekong, Amazon and Congo – the world's three greatest and most diverse tropical rivers – could have drastic impacts on the world's food supply.

"These three river basins hold roughly one-third of the world's freshwater fish species," Kirk Winemiller, lead author of the study and a professor of wildlife and fisheries sciences at Texas A&M University, said in a news release. "The 450 additional dams being planned or under construction in these basins put many unique fishes at risk."

Generally speaking, tropical rivers are less dammed than those in temperate regions, partly because they further away from large human populations and harder to access. Now, however, officials are turning to hydropower to meet the skyrocketing demand for electricity across Africa, Latin America and the south-east Asia. The Amazon dams alone could force people to relocate and increase rates of deforestation.

"Even when environmental impact assessments are mandated, millions of dollars may be spent on studies that have no actual influence on design parameters, sometimes because they are completed after construction is underway," co-author Leandro Castello, an assistant professor of fish conservation at Virginia Tech, explained in the university's release. "A lack of transparency during dam approval raises doubts about whether funders and the public are aware of the risks and impacts on millions of people."

In total, more than 450 large dams are expected to be built in the three river basins. While the exact impacts this will have on production are unknown, researchers estimate that the total loss in fish could be between 550,000 and 880,000 tons a year if 11 of the 12 mainstream dams are constructed on the Mekong - and according to environmental group International Rivers, more than 100 species of fish in the region could face extinction.

"Long-term ripple effects on ecosystem services and biodiversity are rarely weighed appropriately during dam planning in the tropics," co-author Peter McIntyre, assistant professor of zoology in the Center for Limnology at the University of Wisconsin-Madison, added. "There is good reason for skepticism that rural communities in the Amazon, Congo, and Mekong basins will experience benefits of energy supply and job creation that exceed costs of lost fisheries, agriculture, and property."

That's why researchers have come up with new analytical methods to weigh the costs and benefits of hydropower. This includes accounting for cumulative impacts from dams upon hydrology, sediment dynamics, ecosystem productivity, biodiversity, fisheries, and rural livelihoods throughout watersheds.

Their study was recently published in the journal Science.

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