Keywords: Mammals, Fishes, Salmonids, Floodplains, Salish Sea Currents magazine

Salmon restoration groups are learning how to work with beavers to create better salmon habitat. The process hinges on reducing human-beaver conflicts while taking a natural approach to ecosystem recovery. The beavers are happy to help. 

In the middle of a hundred-plus-page report produced in 2015 by the Jefferson County Conservation District is an aerial photo adorned with computer-drawn lines that perfectly illustrate the sometimes uneasy coexistence of three inhabitants of the Puget Sound region.

The photograph depicts two farms outside the town of Chimacum, on the eastern edge of the Olympic Peninsula. An angled blue line down the center of the photo indicates East Chimacum Creek, which flows into Puget Sound at the north end of the town of Irondale. The line is surrounded by an orange polygon representing the borders of streamside buffers that people have planted to benefit salmon.

And undulating irregularly around the outside of it all is a dotted red line that traces the handiwork of the third creature in question. Beavers have built a pair of dams along this stretch of the creek. The dotted red line demarcates the extent of beaver-caused flooding that took out 10 acres of hayfield on one farm and about three acres of pasture on the other.

“Wherever we plant trees, it seems like [beavers] move in,” says Glenn Gately, a water quality and salmon habitat specialist with Jefferson County Conservation District and the lead author of the 2015 report. The animals’ presence often disrupts both agriculture and salmon recovery projects, as happened with the two farms along East Chimacum Creek.

A sockeye salmon in midair as it attempts to jump over a beaver dam on stream.

A sockeye salmon attempts to jump over a beaver dam on North Creek in Bothell, Washington. Photo: Jeffrey S. Jensen/UW Bothell

Beavers and salmon have lived and co-evolved together in the watersheds of the Pacific Northwest for thousands of years. An axiom popular among beaver advocates holds that “beaver taught salmon to jump” – calling to mind images of the fish leaping over beaver dams on their way upstream to spawn.

But today, the effort to restore salmon habitat is increasing human-beaver conflicts. And in some parts of the Puget Sound region, strategies to mitigate these conflicts are running headlong into regulations intended to protect salmon. Many biologists and managers envision a more holistic approach to the region’s watersheds that would leverage the natural affinity between beavers and salmon while remaining mindful of human needs. So far, however, a lack of solid science is hampering such an approach.

Beaver benefits

In the last two decades, biologists have become increasingly aware of beavers’ contributions to salmon habitat. “Beavers create complexity,” says Elyssa Kerr, executive director of Beavers Northwest, a nonprofit that promotes human-beaver coexistence in Western Washington. “And complexity is good for salmon.”

The ponds and intricate side channels that form behind beaver dams provide slow-moving water that allows young salmon to rest, woody debris that helps them hide from predators, and a rich banquet of insect life for food.

“Beaver ponds are this amazing rearing habitat for juvenile salmon, particularly coho, because coho spend up to a year in freshwater streams,” Kerr says. In the Stillaguamish watershed, researchers have traced a dramatic reduction in the number of young coho the river system can sustain due almost entirely to the loss of beaver ponds

Often, when beavers build dams on stream reaches enrolled in programs like CREP, “the flooding is extending way beyond the buffer that that farmer intended to include in the program,” says Sierra Young, a conservation planner with Jefferson County Conservation District.

Beaver ponds also provide a place for adult salmon to rest as they travel upstream to spawn. Sediment tends to settle out of the water column in a beaver pond, producing a stretch of exceptionally clean, clear water just below a dam: ideal salmon spawning habitat.

By slowing the flow of water through a river system, beaver dams reduce the effect of scouring winter floods that can destroy salmon redds, while keeping water levels higher during the summer dry season.

And although downed trees and gnawed shrubs are an obvious sign of beaver presence, in the long run the animals’ activities tend to increase streamside vegetation, providing shade and cooler water temperatures that benefit salmon. The still water of beaver ponds also contributes to groundwater recharge, often cooling the water by several degrees downstream of a dam.

What’s more, beavers begin to work their magic on the landscape rapidly. “It's always a shock to see how quickly places can be rewilded with the assistance of beavers,” says Shawn Behling, assistant furbearer biologist with the Washington Department of Fish and Wildlife, describing the array of fish, bird, amphibian, insect, and even mammal life that soon appears in the vicinity of a new beaver dam. “It's just such a miraculous change, almost within weeks.”

Hunting and trapping

All of this ought to make beavers a natural ally of humans in ensuring healthy salmon populations. But that’s not always how things play out in practice, due to the legacy of European settlement that removed both beavers and salmon from the landscape and subsequent policies that now aim, albeit often in an uncoordinated way, to bring both animals back.

Beaver were widely hunted and trapped for their pelts, and nearly extirpated from Washington State by the mid-1800s. Settlers diked and drained wetlands, straightened stream channels, and generally undid the beaver-created complexity in Western Washington’s watersheds. They laid out agricultural fields – often growing crops or pasture right up to the edge of stream banks – as well as towns, roads, and other infrastructure without much thought for the historical presence of beavers.

Sometimes, though, a few clues remain. Along the right side of that aerial photo of the two beaver-flooded Jefferson County farms in the 2015 report is State Route 19, otherwise known as Beaver Valley Road.

Aerial map image with markings that indicate flooded farmland (area between the orange and red lines) caused by beaver dams.

Map showing flooded farmland (area between the orange and red lines) caused by beaver dams in Conservation Reserve Enhancement Program (CREP) buffers. Map: Jefferson County Conservation District

As trapping and habitat loss reduced beaver populations, fishing and habitat loss did the same for salmon. Then, around the turn of the 21st Century, three things changed: Puget Sound Chinook salmon were listed as threatened under the federal Endangered Species Act, setting off a push for habitat restoration to benefit Chinook and other salmon species. Washington State banned leg-hold traps, making beaver trapping more expensive and onerous. And the price of beaver pelts in the international garment trade declined, further reducing trapping pressure on the animals and contributing to a resurgence of beaver populations in the state (946 beavers were killed by trappers in Washington State in 2020, the most recent year for which data are available).

It's complicated

Beavers and salmon are so tightly linked that efforts to create salmon habitat also often create good homes for both. At the most basic level, the semi-aquatic rodents require a water source with woody vegetation nearby for food. One of the simplest and most widespread types of salmon habitat restoration– planting streamside buffers of trees and shrubs to provide cool shade and improve water quality – transforms a location not quite suitable for beavers into one that is perfect for them.

One strategy for dealing with beavers redesigning a restoration project is to design projects with beavers in mind in the first place.

“I have heard from many restoration practitioners throughout our region about beavers very commonly showing up at restoration sites,” says Kerr. Restorationists favor plantings of hardy, fast-growing tree species such as willows – which also happen to be a favorite food of beavers. “And so beavers are like: ‘Wow, cool, thanks. This is perfect.,’” Kerr says.

More complex and extensive salmon restoration projects tend to attract beavers, too. Such projects frequently aim to slow water down, make banks less steep, re-meander streams, or dig out pools and side channels for rearing habitat. “All of those things are beaver-friendly,” Behling says. In other words, salmon restoration creates complexity, and complexity is good for beavers.

Newly planted vegetation in blue plastic tubes surrounded by standing water caused by beaver damming.

Restoration plantings (seen in blue tubes) in a riparian buffer on a farm in Chimacum are negatively impacted by flooding due to a beaver dam. Photo: Sierra Young/Jefferson County Conservation District

But it’s not always easy to accommodate beaver activities on the working agricultural lands where a lot of salmon restoration takes place. The federal Conservation Reserve Enhancement Program (CREP) pays farmers to create and maintain riparian buffers up to 180 feet wide on farmland. Since 1999, more than 207,000 acres of land have been enrolled in CREP in Washington State, and salmon habitat restoration has taken place along 925 miles of stream.

Often, when beavers build dams on stream reaches enrolled in programs like CREP, “the flooding is extending way beyond the buffer that that farmer intended to include in the program,” says Sierra Young, a conservation planner with Jefferson County Conservation District. That’s what happened at those two farms on East Chimacum Creek.

In turn, such experiences shape the views of others in the community. “A lot of farmers who are still hoping to come on board for [restoration] work were very hesitant because they just didn't want the potential for flooding,” says Sarah Doyle, program manager with the North Olympic Salmon Coalition, which has been doing salmon restoration work in the Chimacum Valley for more than three decades.

Other times, the problem is that beavers move into restoration sites and contribute to creating salmon habitat – but not quite in the way that human restorationists or bureaucratic requirements might have envisioned.

If restorationists design a sinuous stream channel with a gravel bed for salmon to spawn in, when beavers build a dam and create a sprawling pond instead the project may look like a failure – even though the site now hosts excellent salmon rearing habitat and contributes to good spawning habitat downstream.

In addition, landowners participating in CREP, and other habitat restoration programs must often ensure a certain rate of vegetation survival – a requirement that sounds reasonable, until beavers move in and change what plants can thrive there. “Often your performance standards aren't being met, even though the habitat is great,” says Kerr.

New strategies

One strategy for dealing with beavers redesigning a restoration project is to design projects with beavers in mind in the first place, Kerr says. And there are ways to manage beaver-caused flooding that impinges on agriculture or other human activities. A device called a pond leveler came into widespread use in the United States during the 1990s: a long, flexible plastic pipe that is embedded in a beaver dam and draws the water down to a manageable level, helping humans and beavers share the landscape.

But since around 2019, beaver management practitioners working in King and Snohomish Counties say they have had trouble securing the necessary permit – a Hydraulic Project Approval or HPA, issued by the Washington Department of Fish and Wildlife, to install pond levelers on beaver dams.

A large wire cage placed in the middle of a beaver dam that crosses a stream.

A notch exclusion fence, seen here, is a large wire cage designed to prevent beavers from accessing and repairing a ‘notch’ created by humans in a dam. Photo: Beavers Northwest

The difficulties stem from concerns that the devices may represent a barrier to the movements of salmon. “If there are fish that need to pass or migrate in the area where a pond leveler needs to be installed, our hydraulic code rules say that we need to provide fish passage through that structure,” says Elizabeth Bockstiegel, statewide HPA coordinator at WDFW.

The situation has prompted beaver management practitioners to develop a workaround, a new type of device known as a notch exclusion fence. This is a large wire cage that prevents beavers from accessing and repairing a human-created ‘notch’ in a dam that brings the water level down. It’s modeled on devices used to keep beavers from building dams across road culverts – which haven’t aroused the same regulatory suspicion as pond levelers.

But these devices aren’t as user-friendly as pond levelers, beaver management practitioners say. They are more complex to build and aren’t as reliable at managing water levels in a beaver pond.

"I do think notch exclusion fences are a workable solution in this time where pond levelers are not easily permitted,” says Ariana Winkler, who coordinates the Living with Beavers program at the Snohomish Conservation District. But, she adds, “In my experience, they require more frequent monitoring and maintenance for debris flowing through them and for beaver attempts to bypass the device.”

The ease of use and reliability of devices like pond levelers are important because landowners are more willing to coexist with beavers if it isn’t a big hassle, says Alex Pittman, a watershed steward with Snohomish County. “Dismissing that management technique out of hand may end up being a net negative for our ecosystems and fish populations,” he says.

What’s more, there’s little hard evidence that pond levelers block salmon passage – or that notch exclusion fences more easily permit it. “There's a lot of assumptions and no science,” says Jennifer Vanderhoof, a wildlife biologist with King County and president of Beavers Northwest. “Anybody that I've talked to, no matter what they think, they're in agreement that we need data.”

Studies needed

Vanderhoof is working to launch a study that would track hatchery salmon fitted with passive integrated transponders, or PIT tags, to see where and how they move past beaver dams. But finding an appropriate location has been difficult, she says.

Vanderhoof and other beaver management practitioners also call for revisiting a provision in the Washington Administrative Code that governs beaver devices. It states that these devices must be installed “so that during low flows, the device will convey enough flow over and around the dam to pass fish.”

It’s not clear how the provision, which went into effect in July 2015, came to be worded in this way. “It's telling us that [a beaver management device] should be doing something that doesn't even happen under natural conditions,” Vanderhoof says. Water generally flows over and around natural beaver dams only during periods of high flow. (Not coincidentally, those are also periods when salmon tend to be heading upstream to spawn.)

The strictness of the provision may be further contributing to scrutiny of pond levelers by some of the WDFW habitat biologists charged with evaluating permit applications for beaver management devices, she and others think.

Pond levelers haven’t attracted as much regulatory skepticism in other parts of the Puget Sound watershed. The North Olympic Salmon Coalition and Jefferson County Conservation District worked together to install nine of the devices in the Chimacum Creek watershed last year.

Staff in the WDFW wildlife division are working with colleagues in the habitat division to provide better guidance to habitat biologists about beaver management devices. “One of my goals would be to be able to help have a more unified set of guidelines for biologists when they are issuing permits,” Behling says. “And it's going to be a long road, but we are trying our best.”

Since early last year, Behling and Bockstiegel have pored over existing scientific literature and agency manuals for information about beaver devices and fish passage. But, says Bockstiegel, “there hasn't been a lot that we've seen that we could put together in a guidance because there's just not much out there.”

About the author: Sarah DeWeerdt is a Seattle-based freelance science writer specializing in biology, medicine, and the environment. Her work has appeared in publications including Nature, Conservation, and Nautilus.

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