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Balancing hydropower and biodiversity in the Amazon, Congo, and Mekong

What was the main motivation for doing the research? 

Two observations triggered this collaborative effort: the awareness that the number of planned dams is rapidly increasing in earth’s most biodiverse aquatic systems, and the observation that dam construction has suffered, and continues to suffer, from a skewed benefits/costs debate. One has only to look up reports on the Belo Monte dam construction in Brazil to appreciate this concern.

And then the question is where to find the data. For the Congo basin, Belgian ichthyologists have been key contributors to the IUCN database, which therefore was pre-adapted to act as the primary source of information to address this subject.

What did you discover? 

Nearly one third of the world’s freshwater fish species live in three large tropical rivers, the Amazon, Congo and Mekong. While hydropower development was rather limited in these basins, now an additional 450 dams are planned or already under construction.

Large dams diminish fish diversity, block migration routes, and reduce fish access to seasonal floodplains downstream. Upstream river stretches become homogeneous and often less productive. Trapped sediments alter biogeochemical processes with an impact on a large geographical scale and fish passages are often unsuccessful or even harmful.

What does this change towards society, applications or scientific progress?

We assert that the real benefits and costs of large hydropower projects are rarely assessed in a correct and transparent way. Three quarters of these dams cost on average twice as much as initially planned. Conversely, effects on biodiversity, fisheries and other ecosystem services are underestimated. We are sceptical that rural communities in the three basins will experience benefits of energy supply and job creation that make up for the loss of fisheries, agriculture and property. In a subsequent letter to Science, Fearnside even raises the question whether a massive dam-building plan is should exist in the first place.