Humans have drastically altered America’s river systems, engineering the landscape through such means as constructing dams and dredging to create ponds and lakes. Billions of dollars of federal, state, and private funding are now being allocated to restore America’s rivers to their “natural” state.

But what, ask some researchers, is their natural state? Although the answer may not be clear, there is one animal whose importance cannot be ignored: the beaver.

In a recent paper in the journal BioScience, Denise Burchsted, a graduate student in UConn’s geosciences program in the College of Liberal Arts and Sciences, explains why the beaver is one of the most important engineers of the country’s water system. She and her colleagues argue that beaver activity must be taken into account when planning river management, and that the animals themselves perform some of the best restoration.

“There’s no mistake that our rivers have changed a lot over the past 400 years,” says Burchsted. “The rivers didn’t look anything like what we think is a natural river these days – there was probably much more debris, things were more swampy, and there were many threads in different directions. Our waterways are undoubtedly different due to human management.”

Burchsted worked on this research with Melinda Daniels, formerly on UConn’s geography faculty and now at Kansas State University; Robert Thorson of UConn’s geosciences department; and Jason Vokoun of the Department of Natural Resources and the Environment.

When scientists investigate the history of American rivers, they typically look at a time frame between 500 and 4,000 years ago, before Europeans came to the U.S. Current restoration efforts typically involve several facets, including maintaining fish populations, limiting sediment deposition or erosion, and limiting nutrients in the water. But while these goals are supported by our society, Burchsted says they’re not necessarily what the rivers were like thousands of years ago.

Most people’s vision of a perfect stream or river is just a part of what it used to look like, she says. Babbling rivers that flow straight and deep in one direction are often actually the result of human modifications. But that’s just one part of the system, which should also include wet meadows and ponds.

Unlike human-made dams, beaver dams are small, porous, and have several channels flowing over and around them, so water – and fish – can penetrate or circumvent them. This is especially important for fish like salmon, which live part of the year in the ocean and travel upstream in rivers to spawn. If these fish can’t get past human dams, says Burchsted, the population crashes, as has been the fate of the Atlantic salmon that used to be plentiful in Connecticut’s rivers.

Fish populations living in the pools created behind beaver dams are generally larger, more diverse, and have larger individual fish than those around human dams, she says. And beaver dams not only allow for the maintenance of fish populations, but they also create a landscape rich in sediments and nutrients. In addition, when a stream eventually begins to flow around a beaver dam, the beavers will move their dam in response. As each dam traps sediments, it stores them and, when the dam is breached, creates what are known as beaver meadows.

Many people view beavers and their dam-building activities as a nuisance, since they can alter stream flows enough to interfere with roads and private property.

“We don’t allow for things to move,” says Burchsted. “Nature moves, but we don’t.”

Overall, she says, beavers are key to restoring rivers in natural areas because they create habitat for fish and animals that live near the edges of waterways, and they create diversity at the landscape level.

“When we do river restoration, we need to think about the whole system, not just a particular pond,” she says. “In the pond, there may be few species, but in the whole network, there will be a lot more if there are many habitat types.”

Natural water networks have lots of barriers in them, she adds, such as bedrock waterfalls and debris dams created by dead trees. These blockages are important for creating habitat for fish and other animals in the streams. Human engineering has removed many of these small blockages, and subsequently has reduced habitat for wildlife.

So, what should be done about beavers in American rivers? Burchsted’s paper presents some testable hypotheses for looking at how beavers impact landscape dynamics, and she focuses her research on areas, such as parks and preserves, where beavers are allowed to roam free. She stresses, however, that she has no good solution for beaver activity that interferes with human settlements.

“As the climate crisis keeps moving, we have to learn to live in the ecosystems we live in,” she says. “I can’t resolve the conflict of beavers interacting with humans.”