Dams and Reservoirs Used for Hydropower Threaten World's Rivers

(Bloomberg) -- Large dams and reservoirs built to provide renewable energy around the world are one of the biggest threats to global river health, a new study has found.

Just one-third of the world’s longest rivers are free flowing, with 60,000 large dams used to provide hydropower to populations from Brazil to China blocking most main waterways, according to the research from McGill University and the World Wildlife Fund Inc.

Long seen as an effective way to move on from burning fossil fuels, building the infrastructure for hydropower prevents rivers from flowing naturally, which harms agriculture, biodiversity, and access to water supplies.

The report claims to be the first global assessment of river health and examined 12 million kilometers (7.5 million miles) of rivers. The world’s only remaining free-flowing rivers can now be found in underpopulated areas of the planet including the Arctic and the Amazon Basin, the researchers said.

“Free-flowing rivers are important for humans and the environment alike, yet economic development around the world is making them increasingly rare,” said lead author Gunther Grill at Montreal’s McGill.

Climate change is also threatening rivers as rising global temperatures affect water flow and quality. However, efforts to combat climate change by transforming energy systems to be less carbon intensive mean that the environmental impact of building dams needs to be factored into planning decisions. Some 3,700 hydropower dams are currently planned or under construction, the report said.

Statkraft AS, Norway’s largest power producer, said earlier this month that extreme weather events caused by climate change meant that the company had to more than double its spending to reinforce dams to withstand heavy rains.

To contact the reporter on this story: Jeremy Hodges in London at jhodges17@bloomberg.net

To contact the editors responsible for this story: Reed Landberg at landberg@bloomberg.net, Andrew Reierson

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