Dams in the Amazon basin have profound adverse environmental impacts on the region’s river system, and the further construction of planned dams is likely to increase the scale and complexity of these effects. This assessment is presented in a Perspective article published in Nature this week. The work raises the question of whether the potential green benefits of hydropower generation through the construction of dams outweigh the costs of the enormous anticipated damage to the most diverse and productive river system in the world.

Most assessments of the environmental impacts of damming Amazonian rivers have focused on local-scale effects within the vicinity of each dam. Edgardo Latrubesse and colleagues devise a new tool for quantifying the current and expected environmental consequences of built and proposed dams in the whole of the Amazon basin. Their analysis highlights how impacts vary by region, according to the number of current and future dams, and explores the vulnerability of the system to changes in sediment flow. For example, the Tapajos region is forecast to suffer huge hydrological impacts, owing to the large number of dams planned (90) and constructed (28) along this major tributary. Research indicates that the Tapajos river is home to unique fish and bird species that are considered to be threatened by existing and planned dams.