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WWF works to sustain the natural world for the benefit of people and wildlife, collaborating with partners from local to global levels in nearly 100 countries.
It’s just before dusk, and the sun casts gold flourishes on the slow ripples of the Potomac River. Trekking through underbrush along the riverbank, Michele Thieme pauses to survey the scene.
“There’s a kingfisher looking for his dinner,” she says, gesturing downstream as a cobalt-crested bird swoops toward the water. In the other direction, fishermen cook their own fish dinner over a smoky campfire, and the scent wafts downwind. “See?” she says with a smile. “So much life depends on rivers.”
As a lead freshwater scientist at WWF, Thieme is especially attuned to that fact. She’s been studying river ecosystems for more than 20 years. But while her work has taken her from Arizona to Bhutan to the Democratic Republic of the Congo, her fascination with rivers was first sparked right here, near Washington, DC—with a canoe and a fishing net—when she was a child.
“The Potomac provides drinking water for the region,” she says. “And from here to the Chesapeake Bay, it’s relatively well-connected. Each spring, shad and herring still migrate from the ocean up to Great Falls”—just north of where she stands.
Unfortunately, such stretches are rare for large rivers. Around the globe, rivers are becoming more and more fragmented as they succumb to the impacts of human development: roads, levees, and dikes transecting floodplains; dams constructed to generate electricity; water diverted for drinking and agriculture. Combine these, and the world is losing its free-flowing rivers at a dizzying pace.
Opportunities to protect the free-flowing rivers that remain are fast disappearing, too. With the current global boom in hydropower, dam construction is only accelerating. In addition to the estimated 60,000 large dams (dams with the capacity to generate one megawatt of power or more) that already exist worldwide, another 3,700 large hydroelectric dams are currently planned or under construction.
Freshwater ecosystems are already suffering the grim consequences of river fragmentation. According to WWF’s 2016 Living Planet Report, which measures the populations of thousands of vertebrate species, vertebrate populations in rivers and wetlands declined 81% between 1970 and 2012. That’s a larger plunge than occurred in any other type of habitat.
Dave Tickner, chief freshwater adviser at WWF-UK, calls the report “scary reading.” “The decline that’s happened just in my lifetime is astonishing,” he says. “We need to do something before it’s too late.”
Recognizing the urgent need to assess the state of rivers on a global scale, Thieme, Tickner, and colleagues set out in 2015 to reconceptualize a WWF report on free-flowing rivers that had been released around 10 years earlier, this time designing new research with the express intent of advocating for policies aimed at protecting some of the rivers that remain.
But the scientists quickly hit a hitch: The conservation community had never really agreed on how to define a free-flowing river.
“The older definition didn’t take into account so many of the factors that can affect river connectivity,” says Bart Geenen, head of freshwater programs at WWF-Netherlands. “It said if a river runs more than 1,000 kilometers without a dam, it’s free-flowing. But how relevant is that threshold? What if there’s no dam, but a lot of dikes or dredging? Previous studies couldn’t account for that.”
There was yet another, bigger problem: an astounding lack of information about the world’s rivers—and especially about the factors that affect river connectivity. Of the world’s approximately 60,000 major dams, for instance, the geographic location of only a third was cataloged. In an age when huge amounts of satellite-generated geographic information is available at the tap of a phone—and even the world’s largest beaver dam can be seen from space—a data gap this size was unfathomable.
"How is it possible that we don’t have databases for where our largest dams are?” asks Geenen. “Or, to make it more complicated, the hundreds of thousands—even millions—of smaller dams, dikes, barrages, and levees? Somehow, no one has compiled that information on a map."
To safeguard the world’s last wild rivers, the scientists would need not only a serviceable definition but also a reliable method to determine what and where rivers truly are free-flowing. So began the Free-Flowing Rivers Assessment, a massive undertaking by WWF and McGill University—along with a group of collaborators including Conservation International, The Nature Conservancy, and several other universities—to create a universally accepted methodology for categorizing free-flowing rivers, as well as a global inventory for identifying the best candidate rivers for protection and restoration.
At its core, the collaboration aims to raise understanding and awareness about the value of free-flowing river systems by mapping where they remain around the globe. Because of its unprecedented depth and scope, Thieme believes, the initiative has significant potential to influence better management of the world’s rivers. Says Thieme: “You can’t manage what you can’t measure."
Rivers are the veins and arteries of the Earth, sustaining people and wildlife and playing an essential role in the world’s water cycle. By depositing nutrient-rich silt on floodplains and deltas, they have produced some of the world’s most fertile agricultural land. Just about every civilization can trace its origins to a major river: Mesopotamia’s Tigris-Euphrates, Egypt’s Nile, and China’s Yellow and Mekong rivers among them.
Geenen notes that in their natural state, rivers are the most biodiverse ecosystems on the planet. And that though they contain 600 times less water, rivers and lakes support, in total, even more fish species than the oceans, with freshwater fisheries providing the main source of protein for more than 500 million people. Then there are the margins where water meets land—the floodplains, wetlands, and riparian zones that are hot spots of ecological diversity.
The master key unlocking these healthy aquatic environments is “flow.” Well-connected river ecosystems allow an essential exchange of water, nutrients, sediments, and species that not only fosters enormous biodiversity but also regulates sediment levels, flooding, pollution, and water purification.
When infrastructure like dams, dikes, and levees is built without thought for the river basin, says Thieme, it inhibits and alters flow, disturbing natural processes from seasonal flooding to fish spawning.
Consider the Mekong River, which begins in the Tibetan Plateau and runs through Laos and Cambodia before reaching the South China Sea via Vietnam. In northern Laos, construction has begun on the highly controversial, $3.5 billion Xayaburi Dam being developed to slake Thailand’s growing thirst for renewable energy. But rivers recognize no national borders; once complete, the dam—the first to span the entire main stem of the lower Mekong and one of 11 slated to be built—is anticipated to cause drastic changes to the river, affecting communities from upstream in China to downstream in Cambodia. It threatens to jeopardize the vulnerable Irrawaddy dolphin, hinder important fish migrations, and radically alter seasonal flow and flooding—key to the fisheries in Tonle Sap Lake, Cambodia, which supply vital protein for some of the poorest people in the region—thus threatening the livelihoods and food security for upwards of 60 million people living downstream.
Thieme acknowledges that dams are critical tools for water resource management and important sources of hydropower. But it’s crucial that they’re built in the right places at the right time, she says. Once one dam is constructed in the wrong location—on a major migration pathway or a river’s main stem, for example—it’s incredibly difficult and expensive to return the river to its natural state.
For many rivers, though, it’s not just one major dam that impacts flow. “You get a dam built here and there, a bit of development through the floodplains, some wetland drainage so people can use the land for agriculture, and then maybe some people are pumping water out of the river to irrigate land for urban use or for use in industry,” says Tickner. “When rivers lose their connectivity, it’s often death by a thousand cuts.”
Almost three years on, WWF has established a scientifically defensible definition of free-flowing rivers that considers this broader set of factors—known among scientists as pressure indicators—that can affect river flow and connectivity. After an extensive review of the available global data, the team ultimately settled on five pressure indicators to include in their assessment—those with the most substantial impacts on river connectivity.
While considering additional factors might seem ideal, says Tickner, information can be hard to come by in remote locations. “You can define a perfect indicator, but if you haven’t got the data, it’s not much use,” he emphasizes. “It’s important that any scientific method we come up with works at the global level, but is also usable at the local levels. It has to be a realistic method that local stakeholders can use, even in developing countries, where politics might be different or capacity levels are constrained.”
But calculating whether a river has good “fluvial connectivity”— a fancy way of saying it’s free-flowing—based on a handful of indicators isn’t as simple as plugging numbers into an algorithm. “It’s much more complex,” explains Günther Grill, a postdoctoral geographer at McGill University and one of the masterminds behind the initiative.
Grill has led the technically rigorous exercise of collecting, calculating, and merging the disparate datasets at the core of the project’s pioneering river-mapping approach. Underlying them all is a master database of the world’s river networks, known as HydroSHEDS. Beginning in 2006, WWF helped create the database, which was derived from a collection of highly detailed NASA satellite images. Another project is the growing map of the world’s major dams—26,000 to date—that Grill and colleagues have amassed by compiling existing research and data. All told, Grill’s sophisticated, intricate analyses can determine the connectivity status of a whopping 8.5 million river reaches—or 22 million miles of waterways.
Yet as with all scientific inquiry, maps and methods are useless if uncorroborated. That’s why Grill’s analyses are verified and fine-tuned through “benchmarking”: comparing his predictions with those of earlier assessments and with the locations of known free-flowing rivers provided by experts or gleaned from on-the-ground observation. “We need to make sure our assessments actually reflect reality and aren’t saying wildly different things,” says Tickner.
So while Grill can most often be found sitting at his computer, he also checks his numbers in the real world. “My daily work is in front of a screen filled with lines and tables representing rivers. But does what I see on the screen and the impacts that I calculate from the data make sense to me when I’m on the ground, looking at the landscape?” he asks.
Grill also helps “downscale” analyses for specific rivers. Building on his global datasets, Grill can add more detailed data from local conservationists and academic institutions—such as the location of proposed dams—to create maps that can become powerful tools for advocacy and conservation planning.
Grill’s first downscaling: the Tapajós River. At roughly 1,200 miles long and with a river basin approximately the size of France, the Tapajós is one of the Amazon River’s largest tributaries. Running through three Brazilian states, the river supports 1.4 million people, 10 indigenous tribes, and incredibly rich habitats that are home to jaguars, giant otters, river dolphins, migratory catfish, and many species found nowhere else.
But the Tapajós is also a large part of Brazil’s energy plans. While global analysis shows that the river is now free-flowing, the local analysis, which includes 44 large dams proposed as part of a vast hydropower complex, reveals that the wild Tapajós could soon lose its connectivity.
Seeing the proposed location for one such dam was eye-opening, Grill says. “Before, it was hard to connect the numbers I observed on the screen with the meaning of these calculations in real life. But when I was there and looking at the building plans for a 50-foot-high wall across a six-mile-wide river, I could imagine how the dam would have the immense impacts my data suggested.”
For other rivers, Grill’s methods have pinpointed disparities between global datasets and on-the-ground perceptions. For instance, Zambians prize the wildness of the Luangwa River. “But shortly after the Luangwa merges with the Zambezi River,” Grill says, “the Cahora Bassa Dam—one of the biggest dams in the world—blocks connectivity. There used to be large migratory fish going up and down the Zambezi into the Luangwa. But because of the dam, that migration is no longer possible. So even though there’s no dam on the Luangwa, we can see how fragmentation downstream is impacting the lower portions of the Luangwa upstream.”
Conversely, Grill continues, “Working with WWF-India, we are trying to identify free-flowing rivers in the headwaters of the Ganga River [also called the Ganges]. With this tool, we are hoping to guide people to, and collaborate on, opportunities for protecting these important rivers.”
“But this is just the first step in prioritizing conservation activities,” Thieme adds. “Just because our global assessment shows a river is free-flowing doesn’t mean it has a high conservation value. Or if a river shows as not free-flowing, that doesn’t mean it’s best positioned for dams. These decisions ultimately need to be made at the basin or national scale, considering multiple social, economic, and environmental factors. The information on river connectivity provides one important consideration within a complex set of concerns.”
It’s this blend of ground-level and global data, and the possibilities revealed by a more comprehensive understanding of river connectivity, that most excites Thieme and others involved in the project. “By providing valuable insights,” she says, “our results will be an asset for advising policy-makers and leaders to make informed decisions—about both the development and protection of the world’s remaining free-flowing rivers and where restoration of free-flowing rivers is most needed.” It’s all about translating data into action.
And while WWF is still gathering data and testing and refining the methodology, the project is already highlighting ample opportunities to guide policy-makers. In Zambia, a national assessment is informing government efforts to determine where best to protect water resources. Similarly, in India, mapping river connectivity is part of an initiative to analyze river health more broadly, evaluating factors such as biodiversity and agriculture. “Our free-flowing river analysis is one tool in a larger toolbox of methods that help us address global river health,” Grill says.
Though the challenges still facing the world’s freshwater ecosystems are daunting, Thieme believes this assessment will herald a new era of attention to rivers around the world. “If we’re going to retain some of the remaining free-flowing rivers as arks of biodiversity in the face of climate change,” she says, “then we’ve got to act right now.”