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Only a third of Earth’s longest rivers still run free

Mapping millions of kilometers of waterways allowed scientists to make the new calculation

By
7:00am, May 10, 2019
Coco River in Brazil

BRANCHES AND BRAIDS  In central Brazil, the Coco River (left) empties into the Araguaia River, or “River of the Macaws,” one of the world’s remaining free-flowing long rivers.

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Free-flowing rivers are an endangered species on Earth. Only about a third of the world’s longest rivers still flow freely along their entire lengths, unchained by dams or reservoirs, scientists report in the May 9 Nature.

The study is the first global map of river “connectivity,” the ability of river water to move freely downstream, across floodplains and into and out of aquifers throughout the year. Connectivity signals river health, and is vital to protect freshwater biodiversity, support fish stocks and deliver sediment to coastal regions threatened by rising seas.

The team, led by geographer Günther Grill of McGill University in Montreal, used satellite data to map 12 million kilometers of rivers around the globe. Of the planet’s 246 rivers that are longer than 1,000 kilometers, only 37 percent still run free, the team found.

Most of the remaining free-flowing rivers are in more remote parts of the world, such as Canada’s Liard River in the Arctic and Zambia’s Luangwa in the Congo Basin.

Cambodian fishermen

coastal shrimp farms

hydropower dam

elephants

Citations

G. Grill et al. Mapping the world’s free-flowing rivers. Nature. Vol. 569, May 9, 2019, p. 215. doi: 10.1038/s41586-019-1111-9.

Further Reading

C. Samoray. Humankind’s water use greater than thought. Science News. Vol. 189, No. 1, January 9, 2016, p. 4.

A. Witze. Dam demolition lets the Elwha River run free. Science News. Vol. 187 No. 1, January 10, 2015, p. 22.

S. Zielinski. Otters provide a lesson about the effects of dams. Science News Online, May 29, 2014.

S. Perkins. Straight flushScience News. Vol. 167, March 5, 2005, p. 152.

E. Francisco. Tales of the undammedScience News. Vol. 165, April 10, 2004, p. 235.

J. Raloff. Salmon hatcheries can deplete wild stocks. Science News. Vol. 159, June 2, 2001, p. 342.

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