ONLY a third of the world’s 242 longest rivers remain free-flowing as dams and reservoirs drastically reduce the benefits that healthy rivers provide to people and nature.
A team of 34 international researchers from Canada’s McGill University, World Wildlife Fund (WWF), and other institutions assessed the connectivity status of 12 million km of waterways worldwide, providing the first assessment of the location and extent of the free-flowing rivers.
They found only 21 of the 91 rivers longer than 1,000km that originally flowed to the ocean still retain a direct connection from source to sea. The last free-flowing rivers are largely restricted to remote regions of the Arctic, the Amazon Basin, and the Congo Basin.
Günther Grill of McGill’s Department of Geography says free-flowing rivers are important for humans and the environment alike, but economic development is making them increasingly rare.
Dams and reservoirs are the leading contributors to connectivity loss. The study estimates there are about 60,000 large dams worldwide, and more than 3,700 hydropower dams are planned or under construction.
“Rivers are the lifeblood of our planet,” says Michele Thieme, lead freshwater scientist at WWF. “They provide diverse benefits that are often overlooked and undervalued.”
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.
The study says climate change will further threaten the health of rivers. Rising temperatures are already impacting flow patterns, water quality, and biodiversity.
“Renewable energy is like a recipe – you have to find the right mix of ingredients to have both a sustainable energy grid and a thriving natural world,” Thieme says.
“While hydropower inevitably has
a role to play in the renewable energy landscape, well-planned wind
and solar energy can be more viable options for rivers and the communities, cities, and biodiversity that rely on them.”