Worldwide, 08 May 2019

New study published on the location and extent of the planet’s remaining free-flowing rivers

In a new scientific paper published in the journal Nature, researchers from an international network of institutions, including IHE Delft, present the first ever global assessment of the location and extent of the planet’s remaining free-flowing rivers. Just over one-third of the world’s 246 longest rivers remain free-flowing.

Free-flowing rivers are those where ecosystem functions and services are largely unaffected by changes to fluvial connectivity, allowing an unobstructed exchange of water, material, species, and energy within the river system and with surrounding landscapes. Connectivity is an important component of healthy rivers that support freshwater fish stocks for hundreds of millions of people, deliver sediment that keeps deltas above rising seas, mitigate the impact of extreme floods and droughts, prevent loss of infrastructure and fields to erosion, and support a wealth of biodiversity.

The study, led by McGill University and the World Wildlife Fund (WWF), concluded that just over one-third (37%) of the world’s 246 longest rivers remain free-flowing, and most of these are restricted to remote regions of the Arctic, the Amazon Basin, and the Congo Basin. Smaller free-flowing rivers were also mapped across wide areas of the developing world, but these results must be interpreted carefully due to limitations in global datasets representing pressure factors.

“The data, methods and results presented in this study will significantly aid the efforts of countries to achieve the Sustainable Development Goals,” said IHE Delft Professor Michael McClain who participated in the study… “even more so if we continue to refine the analyses using detailed local and regional data”.

IHE Delft is working in this direction by continuing research on the topic of free-flowing rivers and incorporating the results to-date in our teaching, capacity development, and advisory services to the international water sector.   

Visit for more information on free-flowing rivers and an interactive map of the world's rivers.

Grill, G. et al. Mapping the world’s free-flowing rivers. Nature 569, (2019).


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