Navigating trade-offs between dams and river conservation

Thieme, Tockner, Grill et al. (2021)

Healthy, connected rivers deliver diverse benefits. They improve food security for hundreds of millions of people with access to freshwater fisheries, deliver nourishing sediments to downstream deltas and agricultural lands, and connect floodplains that help mitigate the impacts of floods, and support a wealth of biodiversity. But rivers and freshwater species are in peril. Recent studies show that two-thirds of the world’s longest free-flowing rivers are impeded by dams or man-made infrastructure, freshwater species have already declined by 84% on average since 1970, and nearly one-third of all freshwater fish face extinction.

Reconciling dams with freshwater system health remains one of the world’s greatest conservation challenges. It is fundamental to the maintenance and recovery of freshwater biodiversity and vital ecosystem services.

Our research, published in the journal Global Sustainability ( / html) shows:

  • If all proposed hydropower dams (~3,700) were built, then over 260,000 km (160,000 miles) of rivers, including the mainstems of the Amazon, the Congo, the Irrawaddy, and the Salween Rivers, would lose free-flowing status.
  • The estimated hydropower generated by proposed dams on free-flowing rivers represents less than 2% of the projected worldwide renewable power needed by 2050 to maintain a global temperature increase below 1.5⁰ C. 
  • The proposed hydropower expansion would result in substantial losses of globally significant biodiversity and associated ecosystem services for a relatively minor contribution toward the needed increase in renewable energy capacity.


There are solutions for navigating trade-offs associated with dam development and river conservation (listed in descending priority): 

  1. Avoid river fragmentation by exploring alternative development options, including non-hydropower renewable energy options such as solar or wind, and avoiding development on high conservation value rivers, sometimes accompanied by formal protections of rivers. Although challenging, this is the most important pathway -- considering the true energy needs of a region at a system scale and planning to avoid negative impacts.
  2. Minimize impacts through strategic or system-scale planning or reregulation of downstream flows. 
  3. Restore rivers through dam removal. 
  4. Mitigate dam impacts through biodiversity offsets that include restoration and protection of free-flowing rivers.

Full citation

Thieme ML et al. (2021). Navigating trade-offs between dams and river conservation. Global Sustainability 4. e18, 1-7.

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