A small hydropower dam in Brazil.
Victor Baptista
A small hydropower dam in Brazil.

The development of small hydropower dams is widespread throughout Brazil and elsewhere in the world, vastly overshadowing large hydropower projects. The proliferation of these smaller dams is a response to growing energy and security needs. Their expansion, however, threatens many of the remaining free-flowing rivers and biodiverse tropical regions of the world — interrupting the migrations of freshwater fishes, on which millions of peoples’ livelihoods depend.

A new University of Washington paper published Jan. 11 in Nature Sustainability quantifies these tradeoffs between hydroelectric generation capacity and the impacts on river connectivity for thousands of current and projected future dams across Brazil. The findings confirm that small hydropower plants are far more responsible for river fragmentation than their larger counterparts due to their prevalence and distribution.

“The cumulative impacts of many small hydropower dams have long been ignored; instead, focus has been on them in isolation, resulting in claims that their impacts are small,” said co-author Julian Olden, a UW professor of aquatic and fishery sciences.

This study was led by Thiago Couto, a recent doctoral graduate in the UW School of Aquatic and Fishery Sciences who is now a postdoctoral researcher at Florida International University.

Dams constrain the movement of migratory fish along river networks and isolate critical habitats, such as spawning and feeding grounds, which may contribute to local extinctions, population declines and collapses of fishery stocks. This makes migratory fish species some of the most vulnerable organisms to hydropower development in the tropics.

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