Researchers recently found that only 90 rivers – roughly one-third of the world’s long rivers – currently remain free flowing without any manmade obstructions. The study, published in science journal Nature, is especially important because it is the first to explore the free flow of rivers on a global level.

“This is the most comprehensive assessment of river connectivity that’s ever been done, and it shows we are losing our longest, free-flowing rivers,” Michele Thieme, lead freshwater scientist at the World Wildlife Fund and one of the analysis’ researchers, told National Geographic. 

The remaining free flowing rivers are in the Congo, Amazon, and Arctic regions — areas with little-to-no human activity or development.

Rivers are crucial to the environment and wildlife. They also help to sustain human life by providing food, water, agricultural irrigation, and energy — but in order to do this, they need to be able to flow unobstructed.

With climate change being one of the greatest global concerns today, hydropower has been one of the leading zero-emission alternatives to the use of fossil fuels. However, dams and levees have become necessary and widely used tools to control and regulate this type of energy, and these prevent rivers from flowing freely.

Scientists estimate that there are 2.8 million dams constructed worldwide, obstructing connectivity and redirecting river flow. 

The report highlighted the negative effects this fragmentation can have on these rivers and their surrounding ecosystems. The wildlife found in and near rivers remain the most heavily impacted. 

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“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 and biodiversity that rely on them,” Thieme told the Guardian.

According to National Geographic, there have been massive reductions in fish populations due to dam construction in the Yangtze River in China, the Columbia River in the US, the Murray-Darling river basin in Australia. 

Lead researcher Günther Grill told the Guardian that necessity, location, and design need to be considered when planning dam construction. The report also encourages planners to factor maintaining river connectivity and potential subsequent environmental changes into relevant decisions. 

To address the environmental issues caused by dams, countries like China have become less reliant on hydropower, while others, like the United States, have attempted to restore their rivers by removing dams.

In 2014, National Geographic reported that such efforts were successful for the Elwha River in the Pacific Northwest, which saw its fish populations return to their natural homes, benefitting the entire ecosystem.

Read More: The World Wastes Nearly 50 Million Tons of Fish Every Year: UN

Other areas of the world are still greatly affected by river fragmentation and loss of connectivity.

“The [global] study grossly underestimates the extent of river fragmentation as [it] only considers very large dams. We believe free-flowing rivers simply don’t exist anymore, at least in Europe,” Carlos Garcia de Leaniz, a professor at Swansea University who led a similar study focused on the UK, told the Guardian.

There are several projects working to change that fact throughout Europe, Nat Geo reports, such as Dam Removal Europe, which aims to remove 30,000 old or obsolete dams clogging the continent’s rivers. 

The scientists involved in the global rivers assessment stated in the report that the data they have collected can help governments dedicated to preservation and restoration manage and monitor their countries’ great rivers and stress the necessity of action.