Only a third of the longest rivers in the world flow freely

Only a third of the longest rivers in the world flow freely

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Just a third of the longest rivers in the world flow freely, reveals a study published in Nature.

  • Dams and reservoirs are the main contributors to the loss of connectivity of rivers. There are about 60,000 large dams on the planet and more than 3,700 are in planning or construction
  • In Argentina, the Santa Cruz River, the last glacial river in Patagonia that runs free from the mountain range to the sea, is today seriously threatened by the construction project of the Condor Cliff - La Barrancosa dams.

Climate change is a growing threat to the health of the world's rivers, due to direct impacts and as countries increasingly turn to hydropower as a renewable energy option. Only a third (37%) of the 246 longest rivers in the world continue to flow free, according to a new study published in the scientific journalNature: "Mapping the World’s Free-Flowing Rivers." Dams and reservoirs are dramatically reducing the many benefits that healthy rivers bring to people and nature across the planet.

A team of 34 international researchers from McGill University, World Wildlife Fund (WWF) and other institutions [i] analyzed the connectivity status of 12 million kilometers of rivers around the world, providing the first global assessment of the location and extent of of the rivers that flow freely on the planet. [ii]

Among other findings, the researchers determined that only 21 of the world's 91 rivers that were more than 1,000 kilometers long and originally flowed to the sea still retain a direct connection from their source to their mouth to the sea. The free-flowing rivers that remain on the planet are largely limited to remote regions of the Arctic, the Amazon basin and the Congo basin, in Argentina the Santa Cruz River is the last glacial river in Patagonia that runs free from the mountain range to the sea, today threatened by the construction project of the Condor Cliff - La Barrancosa dams. "The world's rivers make up an intricate network with vital links to land, groundwater and the atmosphere," said the lead author, Günther Grill, from the McGill Department of Geography. “Free-flowing rivers are important to both humans and the environment, but economic development around the world is reducing them. Our study uses satellite imagery and other data to examine the extent of these rivers in greater detail than ever. "

Dams and reservoirs are the main contributors to the loss of connectivity of rivers. The study estimates that there are around 60,000 large dams globally and more than 3,700 hydroelectric dams are currently planned or under construction. They are generally planned and built at the level of individual projects, making it difficult to assess the real impact on an entire basin or region.

“In Argentina, the fate of the last free river in Patagonia that runs from the Cordillera to the ocean, the Santa Cruz River, is threatened. The two dams that are under construction and could modify the levels of Lake Argentino, intensifying the negative consequences for the residents of the place and threatening the glaciers themselves, not only Perito Moreno but the rest of those protected by Los Glaciares National Park, -the second most visited in Argentina after the Iguazú National Park- receiving around one million tourists each year, with a high impact on the regional economy. That is why for a long time we have formed the Coalition "Rio Santa Cruz Sin Dams ”, together with Fundación Ambiente y Recursos Naturales (FARN), Aves Argentinas, Banco de Bosques, and other NGOs and we work together with other NGOs such as Aves Argentinas, FARN, Banco de Bosques and many more, asking that this project be reviewed and the construction of the dams is suspended and the Santa Cruz River is kept as a free river“, Says Manuel Jaramillo, General Director of Fundación VIda Silvestre Argentina, the organization associated with WWF in our country.

"Rivers are a vital part of our planet," said Michele Thieme, freshwater scientist and leader of WWF's free-flowing rivers initiative. "Rivers provide a wide variety of benefits, which are often underestimated and overlooked. This map, the first of its kind, on the rivers that continue to flow freely in the world will help in making decisions to prioritize and protect the value that rivers give to people and nature.

Healthy rivers support freshwater fish populations that improve food security for hundreds of millions of people, carry sediments that keep deltas above rising sea levels, mitigate the impact of extreme floods and droughts, prevent loss of infrastructure and agricultural fields due to erosion, and they maintain great biodiversity. Disruption of river connectivity often diminishes or even eliminates these critical ecosystem services.

Protecting free-flowing rivers is also vital to saving the biodiversity of freshwater systems. Recent analyzes of 16,704 wildlife populations globally demonstrated that freshwater species populations experienced the largest decline among all vertebrates in the past fifty years, declining an average of 83% since 1970.

The study also notes that climate change will further threaten the health of rivers around the world. Rising temperatures are already affecting flow patterns, water quality and biodiversity. Meanwhile, as countries transition to low-carbon economies, hydropower planning and development accelerates, increasing the need to drive energy systems that reduce overall environmental and social impact.

"Renewable energy is like a recipe where you have to find the right combination of ingredients to have a sustainable energy grid and a planet that can thrive," added Thieme. "While hydropower plays a role in the field of renewable energy, well-planned wind and solar energy can be better options for the rivers, communities, cities and biodiversity that depend on them."

“When we propose the suspension of the project of the dams on the Santa Cruz River, what we do is oppose a bad business from the technical, environmental, economic and social aspects and seek that our last great free river can continue like this. From the “Rio Santa Cruz Without Dams” coalition we seek a true paradigm shift in terms of energy production and consumption, so that state resources comply with the commitments to promote renewable energy and energy efficiency policies. We demand the promotion of an energy efficiency policy that promotes the efficient use of it and that allows to contribute to the reduction of Greenhouse Gas emissions, to protect our renewable resources, to favor that energy services are provided to a minor cost and, in this way, also to take care of the economy ”, Jaramillo highlights.

The international community is committed to protecting and restoring rivers in accordance with the 2030 Agenda for Sustainable Development, which requires countries to monitor the extent and condition of water-related ecosystems. This study presents the methods and data necessary for countries to maintain and restore free-flowing rivers around the world.


[i] Contributing institutions:

McGill University, WWF-US, WWF-NL, WWF-UK, WWF-Mediterranean, WWF-India, University of Basel, Joint Research Center (JRC), WWF-China, WWF-Canada, WWF-Zambia, WWF Greater Mekong Program , The Nature Conservancy, University of Nevada, WWF-Malaysia, IHE Delft, WWF- Germany and HTWG Konstanz, King's College London, Umeå University, Swedish University of Agricultural Sciences, University of Washington, Harvard University, University of Wisconsin-Madison, Conservation International, WWF-Mexico, WWF International, Stanford University, Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB), Freie Universität Berlin, WWF-Brazil, Eberhard Karls University of Tübingen.

[ii] First scientific definition of free-flowing rivers:

Rivers where ecosystem functions and services are largely unaffected by changes in river connectivity allowing an unhindered exchange of water, materials, species and energy within the river system and with surrounding landscapes.

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