One third of freshwater fish species at risk from dam projects

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One third of freshwater fish species at risk from dam projects

One third of the world's freshwater fish species could be under threat if the go-ahead is given for hundreds of hydro-electric dams to be built in the Amazon, Congo and Mekong basins.

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

"Large dams invariably reduce fish diversity and block movements that enable migratory species to complete their life cycles. This may be particularly devastating to tropical river fisheries where many species migrate hundreds of kilometres," says the report.

In the Amazon basin, the authors say, 334 dams have been proposed which together could devastate fisheries and lead to deforestation.

The study says that the impacts would extend far beyond the direct effects on rivers to include forced relocation of human populations, and expanding deforestation associated with new roads. The Belo Monte dam, which is being built on the Xingu River in Brazil, would be the world’s third largest but may set a record for biodiversity loss.

Planned dams at the Inga Falls in the Democratic Republic of the Congo could harness 83% of the river’s annual discharge and could divert water and substantially reduce flow for miles downstream.

Six large dams have already been built on the Upper Mekong river, mainly in China, but there are now plans for 11 more on the main river and 88 on its tributaries in Thailand, Cambodia and Laos. 

"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," said co-author Leandro Castello, an assistant professor of fish conservation at Virginia Tech, who studies how global change affects the ecology and conservation of fish and fisheries. "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."

"Species extinctions and basin-wide declines in fisheries and other ecosystem services are certain to accompany new hydropower in the world’s mega diverse tropical rivers," the report concludes.

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