WSDOT

Just over one-third of the world’s 246 longest rivers remain free-flowing, according to a new study published May 8 in Nature. Dams and reservoirs are drastically reducing the diverse benefits that healthy rivers provide to people and nature across the globe.

A team of 34 international researchers from McGill University, World Wildlife Fund, the University of Washington and other institutions assessed the connectivity status of 12 million kilometers of rivers worldwide, providing the first-ever global assessment of the location and extent of the planet’s remaining free-flowing rivers.

Among other findings, the researchers determined that only 21 of the world’s 91 rivers longer than 1,000 kilometers (621 miles) that originally flowed to the ocean still retain a direct connection from source to sea. The planet’s remaining free-flowing rivers are largely restricted to remote regions of the Arctic, the Amazon Basin and the Congo Basin.

“Our findings are quite sobering — ongoing dam construction will continue to dwindle the number of remaining free-flowing rivers,” said co-author Julian Olden, a professor at the UW School of Aquatic and Fishery Sciences. “But, optimistically, the removal of aging and obsolete dams can help reverse this course.”

Healthy rivers support freshwater fish stocks that improve food security 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. Disrupting rivers’ connectivity often diminishes or even eliminates these critical ecosystem services.