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The Beaver Restoration

Guidebook

Working with Beaver to Restore Streams, Wetlands, and Floodplains

Version 2.0, June 30, 2017

Photo credit: Worth A Dam Foundation (martinezbeavers.org)

Prepared by 

US Fish and Wildlife Service Janine Castro

National Oceanic and Atmospheric Administration Michael Pollock and Chris Jordan

University of Saskatchewan Gregory Lewallen

US Forest Service Kent Woodruff

Funded by

North Pacific Landscape Conservation Cooperative
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Recommended citation: Pollock, M.M., G.M. Lewallen, K. Woodruff, C.E. Jordan and J.M.

Castro (Editors) 2017. The Beaver Restoration Guidebook: Working with Beaver to Restore 

Streams, Wetlands, and Floodplains. Version 2.0. United States Fish and Wildlife Service, 

Portland, Oregon. 219 pp. Online at:

https://www.fws.gov/oregonfwo/promo.cfm?id=177175812
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Contents

Acknowledgements ...................................................................................................................iv

About This Guidebook..............................................................................................................vi

Michael M. Pollock, Janine Castro and Gregory Lewallen

Section I - Beaver Ecology..........................................................................................................1

Chapter 1—Effects of Beaver Dams on Physical and Biological Processes ........................2

Gregory Lewallen, Michael M. Pollock, Chris Jordan and Janine Castro

Chapter 2—Frequently Asked Questions about Beaver .....................................................20

Gregory Lewallen, Janine Castro, Chris Jordan and Michael M. Pollock

Chapter 3—Beaver Myth Busters ...........................................................................................43

Gregory Lewallen

Section II - Beaver Restoration and Management ................................................................45

Chapter 4—Watershed Planning for Beaver Restoration Projects.....................................46

Michael M. Pollock, Kent Woodruff, and Chris Jordan

Chapter 5—Relocating Beaver................................................................................................64

Kent Woodruff and Michael M. Pollock

Chapter 6—Beaver Dam Analogues (BDAs) ........................................................................85

Michael M. Pollock, Nick Weber and Gregory Lewallen

Chapter 7— Urban Beaver Population Management........................................................100

Gregory Lewallen, Heidi Perryman, Kaegan Scully-Engelmeyer, Ellen Wohl

Chapter 8—Managing Habitat for Beaver...........................................................................115

Michael M. Pollock and Gregory Lewallen

Chapter 9—Non-lethal Options for Mitigating the Unwanted Effects of Beaver..........117

Michael M. Pollock and Gregory Lewallen

Chapter 10—Beaver Dam Viability Matrix: A User’s Guide ............................................126

Janine Castro

Chapter 11—Beaver Restoration Case Studies ...................................................................132

Gregory Lewallen, Heidi Perryman, Carol Murdock, Mark Beardsley, Daniel Armichardy, Scott Jay 

Bailey, Bob Hassmiller, Sean Bistoff, David Helzer, Kendra Smith, Susan Firor, Janet Hohle, Scott Reid, 

Jessica Doran, Brad Johnson, Mike Claffey, Matt Weaver, David Kliegman, Julie Ashmore, Lauren Rich 

and Cathryn Wild

Section III – Additional Information and Resources..........................................................188

Beaver Resources ....................................................................................................................188

Acronyms and Abbreviations ...............................................................................................190

Literature Cited.......................................................................................................................191

Appendix A. Plant Species Eaten by North American Beaver.........................................212

Appendix B. Subspecies of C. canadensis Considered “Invalid” by ITIS.........................219
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Acknowledgements

This guidebook builds on the hard work and dedication of many people and organizations who have 

recognized the potential of beaver to restore ecosystems. All contributions, insight, and support are 

gratefully acknowledged. Contact information for some of the organizations we found most helpful, 

along with additional reading suggestions, are found in the “Additional Resources and Information”

section at the end of this guidebook.

We have tried to identify, recognize, and fully acknowledge the work and ideas of others, but 

undoubtedly, there are omissions. If there are statements, facts, figures, or images that are not properly 

attributed, please let us know and we will make the appropriate corrections on the next version. Please 

send corrections to Gregory Lewallan at gregory.lewallen@usask.ca.

Principle Authors

Gregory Lewallen, University of Saskatchewan, Saskatoon, Saskatchewan, Canada. 

gregory.lewallen@usask.ca.

Michael M. Pollock, National Oceanic and Atmospheric Administration, Northwest Fisheries 

Science Center, Seattle, Washington. michael.pollock@noaa.gov.

Kent Woodruff, United States Forest Service (retired), Winthrop, Washington.

kentwoodruff@gmail.com.

Chris Jordan, National Oceanic and Atmospheric Administration, Northwest Fisheries Science 

Center, Corvallis, Oregon. chris.jordan@noaa.gov.

Janine Castro, United States Fish and Wildlife Service & National Oceanic and Atmospheric 

Administration, National Marine Fisheries Service, Portland, Oregon. 

janine_m_castro@fws.gov.

Editors

Michael M. Pollock

Gregory Lewallen

Janine Castro

Technical Editor

Ann Sihler

Contributors

Thanks to the numerous individuals who provided case studies, figures and images, with a special 

thanks to those who reviewed the document and offered their suggestions and advice. The following is 

an alphabetical list of contributors to the Beaver Restoration Guidebook.

Armichardy, Dan US Forest Service Leary, Ryan The Klamath Tribes

Armstrong, Bob www.naturebob.com Lev, Esther The Wetlands Conservancy

Beardsley, Mark EcoMetrics, LLC Lundquist, Kate OAEC Water Institute

Bouwes, Nick Ecological Research Moore, Kelly Oregon Dept. of Fish and Wildlife
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Brennan, Matthew Clean Water Services O’Brian, Mary Grand Canyon Trust

Caldwell, Chuck The Beaver Patrol, Juneau, AK Ojala-Barbour Reed The Methow Beaver Project

Conley, Kimberly US Forest Service Portugal, Elijah Utah State University

Fetherston, Kevin R2 Resource Consultants Rustay, Michael Snohomish County Public Works

Firor, Susan Terra Graphics Environmental Slocum, Tom Skagit Conservation District

Frey, Jennifer K. New Mexico State University Smith, Karri K.A. Smith Consulting, Inc.

Gilgert, Wendell Point Blue Conservation Sci. Stengle, James B. Certified Wildlife Biologist (retired)

Hocker, Katherine SE Alaska Sketchbook Stockard, Torre The Methow Beaver Project

Hartman, Heidi Oregon Dept. of State Lands Vickerman, Sara Defenders of Wildlife

Hemphill, Nina US Forest Service White, Seth Columbia River Inter-Tribal Fish Comm.

Hoehne, Suzanne Biohabitats.com, Ohio River Willson, Mary, The Beaver Patrol, Juneau, AK

Weber, Nick Ecological Research

Contributors to Beaver Restoration Case Studies

Armichardy, Dan US Forest Service Hohle, Janet Idaho Office of Species Conserv.

Beardsley, Mark EcoMetrics, LLC Johnson, Brad Johnson Environ. Consulting

Ashmore, Julie Okanogan Highlands Alliance Kliegman, David Okanogan Highlands Alliance

Bailey, Scott Jay Tillamook Esturary Partnership Murdock, Carol Clean Water Services

Bistoff, Sean City of Portland Environ. Services Perryman, Heidi www.martinezbeavers.org

Claffey, Mike Claffey Ecological Consulting, Inc. Reid, Scott The Town of Breckenridge

Doran, Jessica Ecomentrics Rich, Lauren Upper Skagit Indian Tribe

Firor, Susan Terra Graphics Environ. Engineer. Smith, Kendra Bonneville Environ. Foundation

Hassmiller, Bob US Forest Service Weaver, Matt Five Rivers, Inc.

Helzer, David City of Portland Environ. Services Wild, Cathryn Seventh Generation Institute

Funding Provided By:

The North Pacific Landscape Conservation Cooperative

US Fish and Wildlife Service

National Oceanic and Atmospheric Administration

US Forest Service

Finally, many thanks to all the participants that attended and provided feedback at the Beaver 

Restoration Workshops held in Oregon, Washington, California and Alaska, and to the invited 

speakers, Melissa Babik of the Mid-Columbia Fisheries Enhancement Group, Shelly Blair, California 

Department of Fish and Wildlife, Mark Cookson, US Fish and Wildlife Service, William Meyer, 

Washington Department of Fish and Wildlife, Thomas Stahl, Oregon Department of Fish and Wildlife

and Charlie Corrarino (retired), Oregon Department of Fish and Wildlife. Also, many thanks to Brian 

Turner, Mary Anne Schmidt and Patrick Edwards of Portland State University, Environmental 

Professionals Program, for helping to organize those workshops.
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About This Guidebook

Michael M. Pollock, Janine Castro and Gregory Lewallen

Beaver as a Partner in Restoration

Increasingly, restoration practitioners are using beaver to accomplish stream, wetland, and floodplain

restoration. This is happening because, by constructing dams that impound water and retain sediment,

beaver substantially alter the physical, chemical, and biological characteristics of the surrounding river 

ecosystem, providing benefits to plants, fish, and wildlife. The possible results are many, inclusive of: 

higher water tables; reconnected and expanded floodplains; more hyporheic exchange; higher summer 

base flows; expanded wetlands; improved water quality; greater habitat complexity; more diversity 

and richness in the populations of plants, birds, fish, amphibians, reptiles, and mammals; and overall 

increased complexity of the riverine ecosystems.

In many cases these effects are the very same outcomes that have been identified for river restoration 

projects. Thus, by creating new and more complex habitat in degraded systems, beaver dams (and their 

human-facilitated analogues) have the potential to help restoration practitioners achieve their 

objectives. Beaver have become our new partner in habitat restoration.

Yet even though the potential benefits of restoring beaver populations on the landscape are numerous, 

so, too, is the potential for beaver/human conflicts. These conflicts can arise from an overlap of 

preferred habitats by both humans and beavers, misunderstandings of how beavers modify their 

habitats, and a lack of planning or use of adaptive management on restoration projects. Reviewing the 

information provided in this guidebook will help interested parties approach beaver-based restoration 

from a more informed perspective, so that they can manage expectations and increase success.

Goals of This Guidebook

This guidebook provides a practical synthesis of the best available science for using beaver to improve 

ecosystem functions. If you are a restoration practitioner, land manager, landowner, restoration funder, 

project developer, regulator, or other interested cooperator, this guidebook is for you.

Our overall goal is to provide an accessible, useful resource for those involved in using beaver to 

restore streams, floodplains, wetlands, and riparian ecosystems. Although the guidebook summarizes

current information about how to use beaver in restoration and conservation, the knowledge base on 

this subject is rapidly expanding. This means that not all of the information provided has been peerreviewed in scientific journals; some of it is instead based on the real-life experience of restoration 

practitioners who are conducting ongoing experiments on using beaver to restore habitat. Thus the 

guidebook is a compilation of the current best available science, and we expect to update it regularly as 

the science progresses, readers provide information from their ongoing restoration experiments, or 

from restoration efforts of which we are currently unaware. See Table 1 for the different types of data 

presented in this document and the relative ranking we used for assessing scientific credibility.

Much of the information presented here is applicable across the beaver’s range, but the guidebook 

focuses on beaver restoration in the western United States. Much of the interest in beaver restoration is 
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occurring in the context of restoring habitat for declining populations of Pacific salmon and trout while 

simultaneously improving stream flows, particularly in drought-prone regions.

Structure and Content

The chapters of this guidebook fall into two broad sections; beaver ecology (chapters 1-3) and beaver 

restoration and management Chapters 4-11. The “Beaver Ecology,” chapters discuss both the general 

life history characteristics and the effects that beaver dams have on physical and biological processes 

within river ecosystems. This is includes “Frequently Asked Questions” about beaver (Chapter 2) and

beaver “Myth Busters” (Chapter 3), which dispel common myths or misperceptions about beaver, 

including those that, unfortunately, can influence funding and permitting decisions. Readers already

familiar with beaver ecology may opt to skip the first section and move directly to the latter portion of 

the guidebook, which addresses topics related to beaver restoration and management.

Chapters 4 through 8 discuss common emerging techniques for using beaver and beaver dams (both 

natural and human created or assisted dams) to improve ecosystems; Chapter 7 discusses urban beaver 

population management strategies and techniques; Chapter 9 describes methods for mitigating the 

unwanted effects of beaver activity; Chapter 10 introduces the Beaver Dam Viability Matrix, which 

grew out of the Project Screening Risk Matrix—one of several tools generated by the River Restoration 

Analysis Tool Project (RiverRAT), a broad federal effort to more efficiently and effectively evaluate 

stream management proposals; and Chapter 11 presents real-life examples of pioneering practitioners 

who have used beaver restoration tools in the field.These case studies include lessons learned that will 

help guide future restoration efforts. 

Future Resources

We originally intended to include a chapter on “Beaver Rules and Regulations” as they pertain to 

restoration in western states, but the process of researching this subject revealed a confusing patchwork 

of state, federal, tribal, and even local rules governing beaver and beaver dams that varies by land 

ownership, state and federal agencies, and other factors. Untangling the web of rules and policies into a 

tractable discussion was beyond the scope of this initial document, but we hope to pursue this topic in 

the future and appreciate any relevant information that readers want to provide.

We have also developed a comprehensive beaver ecology library of more than 1,400 references from 

scientific journals, “gray” literature, websites, legislation, regulations, and presentations that is 

available for readers either in Endnote or as a text document. We have copies of many of the articles 

and are building a library of beaver articles, with particular emphasis on the more obscure references 

that are difficult to obtain from the Internet. Yet, as comprehensive as this library might sound, many 

references related to beaver ecology are not yet included, particularly those from the gray literature. 

We look forward to including additional references as they are provided by readers.

Finally, since this is a “living document”, we will be updating regularly, including the addition of other 

beaver restoration-related products so please check the US Fish and Wildlife website for the latest 

information: https://www.fws.gov/oregonfwo/promo.cfm?id=177175812

We will also be sending out occasional notices when updates to the beaver restoration guide become 

available or additional tools are produced. It won’t be quite as smooth as the automatic software 

updates on your phone or computer, but we will do our best. Thank you for your interest. We hope 

that this guidebook facilitates beaver restoration approaches underpinned by sound scientific 
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principles, such that a more comprehensive, evidence-based understanding of beaver ecology, 

restoration, and management emerges.
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Table 1. Common sources of scientific information (adapted from Washington 

Administrative Code 365-195-905). Information can be considered scientific if its source has the 

characteristics in Table 1. Table 1 provides a general indication of the characteristics of valid scientific information 

typically associated with common sources of scientific information and in general order of reliability. Each source 

of information (including peer-review articles) needs to be evaluated carefully to ensure it contains the 

characteristics described below.

Characteristics

Sources of Scientific Information

Peer 

Review Methods

Logical 

Conclusions, 

Reasonable 

Inferences

Quantitative 

Analysis Context References

A. Research. Research data collected and 

analyzed as part of a controlled experiment (or 

other appropriate methodology) to test a 

specific hypothesis.

X X X X X X

B. Monitoring. Monitoring data collected 

periodically over time to determine a resource 

trend or evaluate a management program.

X X O X X

C. Inventory. Inventory data collected from an 

entire population or population segment. X X O X X

D. Survey. Survey data collected from a 

statistical sample from a population or 

ecosystem.

X X O X X

E. Modeling. Mathematical or symbolic 

simulation or representation of a natural 

system. Models are generally used to 

understand and explain occurrences that 

cannot be observed directly.

X X X X X X

F. Assessment. Inspection and evaluation of 

site-specific information by a qualified 

scientific expert. May or may not involve 

collection of new data.

X X X X

G. Synthesis. A comprehensive review and 

explanation of pertinent literature and other 

relevant existing knowledge by a qualified 

scientific expert.

X X X X X

H. Expert Opinion. Statement of a qualified 

scientific expert based on his or her best 

professional judgment and experience in the 

pertinent scientific discipline. The opinion may 

or may not be based on site-specific 

information.

X X X

X = The characteristic must be present for the information derived to be considered scientifically valid and reliable; O = The 

presence of the characteristic strengthens the scientific validity and reliability of the information derived but is not essential to 

ensure scientific validity and reliability. Note: Many sources of information usually do not produce scientific information 

because they do not exhibit the necessary characteristics for scientific validity and reliability. Information from these sources 

may provide valuable information that supplements scientific information, but it is not an adequate substitute for scientific

information. Nonscientific information should not be used as a substitute for valid and available scientific information. 

Common sources of nonscientific information include (1) anecdotal information (i.e., one or more observations that are not 

part of an organized scientific effort, such as "I saw a grizzly bear in that area while I was hiking"), (2) nonexpert opinion (i.e., 

the opinion of a person who is not a qualified scientific expert in a pertinent scientific discipline, such as "I do not believe there 

are grizzly bears in that area"), and (3) hearsay (i.e., information repeated from communication with others, such as "At a 

lecture last week, Dr. Smith said there were no grizzly bears in that area").
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Section I - Beaver Ecology

Photo Credit: Bob Armstrong (www.naturebob.com)
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Chapter 1—Effects of Beaver Dams on 

Physical and Biological Processes

Gregory Lewallen, Michael M. Pollock, Chris Jordan and Janine Castro

In most of the temperate Northern Hemisphere, beaver historically altered low-gradient, small

stream ecosystems by constructing millions of dams made primarily of wood. Almost every

northern temperate ecosystem that had trees or shrubs growing along streams also once had 

beaver dams. In Eurasia, evidence of beaver has been found in streams as far south as Iraq and 

Turkey, in the Arctic, and stretching from Scotland in the west to Kamchatka in the east 

(Halley and Rosell 2002). In North America, beaver were once found far south into the arid 

environments of Arizona and northern Mexico along rivers such as the San Pedro, Colorado, 

and the Rio Grande (Pattie 1833, Leopold 1972) and occupied all biomes north of the border 

from coast to coast, except for the Arctic, the tip of peninsular Florida, and the dry Great Basin 

and desert country of Nevada and southern California (Figure 1).

Figure 1: Probable historic range of the North American beaver. Adapted from Pollock et al. (2003), as 

modified by Lanman et al. (2012, 2013) and James et al. (2012) for California, and Layne (1965) for 

peninsular Florida. Absence of historic beaver evidence in the Great Basin, interior southern California, 

and southern Florida streams, is not evidence of historic absence of beaver in these regions.
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Historically, beaver dams created streams systems with slow, deep water and floodplain

wetlands dominated by emergent vegetation and shrubs. Geomorphology and plant 

communities of small low-gradient streams were much changed throughout much of the 

Northern Hemisphere after reduction of beaver populations (Rea 1983, Naiman et al. 1988b).

In both Eurasia and North America, beaver populations have generally declined as human 

populations have increased. In both continents, only small populations survived by the end of 

the 19th century (Seton 1929, Nolet and Rosell 1998, Halley and Rosell 2002). The primary reasons 

for the declines were that people trapped beavers either because they were resources for fur or 

oil or competitors for productive valley bottom lands (MacDonald et al. 1995, Mackie 1997, 

Halley and Rosell 2002). 

More recently there has been widespread recognition that beaver dams play a vital role in 

maintaining and diversifying stream and riparian habitat (Pollock et al. 1994, Gurnell 1998, 

Collen and Gibson 2000, Rosell et al. 2005, Gibson and Olden 2014, Burchsted and Daniels 2014). In 

the past century, land managers throughout the Northern Hemisphere have attempted to

reintroduce beaver in areas where they have been extirpated. Today, beaver populations are 

rebounding throughout North America, with the population estimated to be about 10 million 

and reoccupying most of its former range (Naiman et al. 1988b).

Beaver are found across a wide range of aquatic habitat types, but they do have preferences:

 Beaver prefer to build dams on small- to medium-sized, low-gradient streams (<6% 

slope) that flow through unconfined valleys, and generally populate the lowest 

gradient (slope < 1-2%) sites first.

 Beaver generally avoid constrained valleys with high-gradient streams (reviewed in 

Pollock et al. 2003) but will colonize this less-preferred habitat if their population 

densities are high (Müller-Schwarze and Schulte 1999).

 Beaver also occupy large rivers but restrict their dam-building to off-channel habitat 

fed by hyporheic flow, groundwater channels, and tributary channels that flow across 

the floodplains of the larger river channel (Gurnell 1998, Baker and Hill 2003, Pollock et 

al. 2003). They also will build seasonal dams across large rivers during low flow 

conditions.

 Beaver build dams on lakes, wetlands, estuaries and just about any water body where 

additional water can be retained and thus habitat improved (from a beaver’s 

perspective) by building a dam.

In addition to these physical habitat attributes, beaver make use of streams with developed 

riparian areas that contain (1) vegetation for food, and (2) potential construction materials to 

build dams and lodges. Although beavers use a wide variety of trees, shrubs, substrate, and 

herbaceous vegetation as construction material, for food they prefer species from the genera 

Populus and Salix (i.e. aspen, cottonwood, and willows). 
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Hydrology

Increased Water Retention and Base Flows

Beaver impoundments change the spatial distribution of water (groundwater, pond, or 

stream), as well as the timing of its release and residence time in the watershed. Beaver dams 

impound water in ponds and pools, and these impoundments slow the flow of the stream; this

holds the water within the stream reach for longer periods and can increase base flows 

(reviewed in Pollock et al. 2003). Indeed, some perennial streams transform into intermittent 

and/or ephemeral streams following the removal of beaver dams (Finley 1937, Wilen et al. 

1975).

Conversely, reintroduced beaver have transformed some intermittent streams back to 

perennial streams (Dalke 1947, Pollock et al. 2003), and recolonizing beaver have transformed 

slightly losing stream reaches to gaining reaches (Majerova et al. 2015). Losing streams are 

characterized by surface water flowing into the subsurface and not returning to the channel, 

usually associated with local water tables that are lower in elevation than the stream surface. 

Gaining streams, conversely, are characterised by high local water tables where subsurface 

water flows into the stream. Additionally, the ponded water expands the saturated surface 

area of riparian zones, converting previously upland plant communities into wetland plant 

communities. Thus, beaver create wetlands. Slower water velocities, lateral spreading, and 

larger areas of soil saturation contribute to increases in both the surface and subsurface water 

present in a watershed (Naiman et al. 1986, Syphard and Garcia 2001, Pollock et al. 2003, 

Cunningham et al. 2006, Westbrook et al. 2006, Hood and Bayley 2008).

Storage of water within the stream reach is particularly important for many aquatic species 

during low-flow periods, when direct hydrologic inputs are limited. When beaver recolonize 

stream systems, their impoundments increase base flows, as well as recharge and elevate the 

water table (Lowry 1993; Pollock et al. 2003). Furthermore, given that climate change is 

expected to increase drought and reduce snow pack, water storage from beaver 

impoundments may be an effective tool to help mitigate the associated reductions in water 

resources (see Rosemond and Anderson 2003, Lawler 2009). Climate change is of particular 

concern in areas that currently depend on glacial and snow-melt runoff. As water storage in 

the form of glaciers and snow decreases, surface and groundwater storage behind beaver 

dams high in watersheds may provide a buffer for base flows (Beechie et al. 2013).

Hood and Bayley (2008) studied how temperature, precipitation, and beaver activity influenced 

the area of open water in east-central Alberta, Canada, over a 54-year span that included many 

periods of drought. The presence of beaver had a substantial effect on the amount of open 

water in wetlands within the study area. Hood and Bayley’s results indicate that beaver 

played a larger role in maintaining open-water areas than did temperature, precipitation, and 

climate. The authors found that, as sites cycled through beaver occupation and abandonment, 

beavers caused a nine-fold increase in open-water area compared to the same sites without 

beaver. Their findings indicate that “beaver could mitigate some of the adverse effects of 

climate change due to their ability to create and maintain areas of open water.” Hood and 

Bayley conclude by suggesting that “the removal of beaver from aquatic systems should be 
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recognized as a wetland disturbance equivalent to in-filling, groundwater withdrawal, and 

other commonly cited wetland disturbances.”

Decreased Peak Flows

Beaver activity within a watershed generally reduces peak flows and spreads flows out over 

longer time periods. Reducing peak stream flows provides water quality benefits in terms of 

sediment reduction and also retention of water within the watershed as surface or 

groundwater. By slowing the stream flow, beaver impoundments reduce erosive energy and 

increase retention time. During floods, energy is dissipated as the water flows through 

multiple small channels on the downstream side of the beaver dam (Pollock et al. 2003).

Floodplain vegetation alongside and below the dam further dissipates energy as the water 

works its way back to the stream channel (Li and Shen 1973, Woo and Waddington 1990, Dunaway 

et al. 1994, Pollock et al. 2003).

Beaver impoundments attenuate flood peaks by retaining water behind dams and in the 

subsurface. Beedle (1991) estimated that a single full beaver pond on a southeastern Alaska 

island reduced peak flows by more than 5 percent. A series of five large ponds could reduce 

peak flows of a 2-year event by 14 percent and peak flows of a 50-year event by 4 percent.

Also, because ponds are not always at capacity, they can allow for additional storage of flood 

water. For streams with dozens of dams, further reductions in peak flows and stronger 

cumulative effects should be expected (Scheffer 1938, Smith 1950, Naiman et al. 1986, Pollock et 

al. 2003).

Expansion of Habitat Area and Complexity

Beaver dams can create very large and numerous surface pools and ponds, transforming 

moving-water habitats to a combination of moving- and slow-water habitats (Naiman et al. 

1988b, Martell et al. 2006). This increase in surface and subsurface water leads to an expansion 

of riparian and wetland habitats along streams (see Johnston and Naiman 1990ab, Pollock et al. 

2007, Hood and Bayley 2008). Repeated colonization of sites by beaver followed by 

abandonment creates habitat complexity, or heterogeneity, within the watershed (Burchsted et 

al. 2010). After abandonment, open-water wetlands drain and may transform into wet 

meadow habitats called “beaver meadows” (see the subsection below: Habitat-vegetation). In 

beaver-modified habitat, the continual creation, modification, and abandonment of wetland 

patches creates a mosaic of wetlands with a large range of ages and successional stages (Wright 

et al. 2003). The increased heterogeneity, in turn, increases the diversity of habitat types and

plant and animal species, as well as the resiliency of the system to disturbance, specifically 

flooding (Naiman et al. 1988b) and drought (Hood and Bayley 2008). 

Surface water area is most dramatically affected directly upstream of beaver dams, where it is 

collected in ponds and pools. The amount of surface water collected in these low-gradient 

areas ranges greatly, depending on the size and topography of the catchment, the channel 

form, and the water regime of the region. Typically the amount of surface water present 

increases with the number of beaver dams on a stream reach (Johnston and Naiman 1990ab). The 

ponds and pools formed from beaver dams provide important slow-water habitat for birds, 

waterfowl, fish, aquatic invertebrates, mammals, and amphibians. By increasing the amount of
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riparian area, beaver ponds typically provide important habitat for both terrestrial and aquatic 

plants and animals.

Increased Wetland Area

As ponds and pools fill and become deeper, the impoundments force flow laterally, causing 

overbank flow onto floodplains and creation of side channels, as water flows around beaver

dams (Westbrook et al. 2006). These side channels and distributaries provide benefits such as 

alternative aquatic passage, dissipation of stream energy, hydrologic reconnection to the 

floodplain, and increases in the soil saturation area. All of these attributes help to create an 

intricate network of multi-threaded channels and wetlands. 

Evidence of surface water and wetland expansion caused by beaver dam construction is 

plentiful. Many studies have documented creation of and changes in surface water and 

wetland habitats that have resulted from increases in beaver populations. For example, when 

studying the effects of climate and beaver activity in Elk Island National Park in Alberta, 

Canada, Hood and Bayley (2008) estimate that beaver reoccupation of the park caused the total 

area of open water to increase from 365 hectares (in 1948) to 991 hectares (in 1996). In Acadia 

National Park in Maine, Cunningham et al. (2006) found that beaver contributed to an 89

percent increase in ponded wetlands from 1944 to 1997, by converting forested wetlands and 

riparian areas to open water and emergent wetlands and by converting forested upland 

habitat to forested wetlands and riparian areas. In Virginia, Syphard and Garcia (2001) found 

that, from 1953 to 1994, beaver activity in the Chickahominy River watershed accounted for 

only 1 percent of wetland gain, but the animal’s activities accounted for 23 percent of the 

change in wetland types. In a region of northern Minnesota, Johnston and Naiman (1990a) found 

that the number of beaver ponds increased from 71 to 835 between 1940 and 1986 as beaver 

reoccupied the area. 

Increased Groundwater Recharge

Beaver dams can play a critical role in replenishing alluvial aquifers by trapping and storing

water, redirecting surface water onto adjacent floodplains, and forcing water into the 

streambed and banks. Overbank flooding is generally thought to be the main hydrologic 

mechanism for replenishing groundwater in riparian areas (Workman and Serrano 1999, Girard 

et al. 2003, Westbrook et al. 2006).

Subsurface flow patterns may also be affected by beaver impoundments. In two separate 

studies located in Rocky Mountain National Park (in Colorado) and in central Oregon, 

Westbrook et al. (2006) and Lowry and Beschta (1994), respectively, observed groundwater flow 

moving laterally around the dams (i.e., perpendicular to the river) into floodplain soils, then 

downstream, and eventually back in toward the river channel. This “looping” pattern of 

groundwater flow does not always take place; its occurrence depends on topographic relief 

and beaver dam height, which affect the hydraulic gradient between river and riparian area 

(Westbrook et al. 2006). Groundwater flow may also be affected by the location of the beaver 

dam within the valley and the stream’s geomorphology. Furthermore, Westbrook et al. (2006)

found that, in Rocky Mountain National Park, the main effects of beaver on hydrologic 

processes occurred downstream of beaver dams rather than being confined to the near-pond 
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area. In semi-arid streams, the hydraulic head created by beaver dams can affect subsurface 

flows by increasing hyporheic interactions within and downstream of beaver dam complexes 

(Lautz et al. 2006).

During summer low-flow months, groundwater drawdown often can negatively affect 

riparian and floodplain plant communities, especially when rainfall and snowmelt flows have 

already diminished, as well as the frequency and duration of flooding events. In addition

groundwater stored in the soil can be depleted by evapotranspiration. By attenuating the rate 

of water table drawdown during summer low-flow months, beaver dams can provide a 

constant supply of water to the riparian area, via surface and subsurface flow paths (Westbrook 

et al. 2006). This influence on the hydrological processes affects the development of the 

floodplain and riparian areas by maintaining high local water tables and deeper groundwater 

levels. Thus, beaver influence floodplain structure and function (Westbrook et al. 2006).

In addition to mitigating climate change-related decreases in stream flow, via surface water 

storage, beaver increase the amount of groundwater storage and aquifer recharge (Pollock et al. 

2003, Westbrook et al. 2006). This ultimately may be the most important beaver-related factor in 

mitigating effects from climate change because groundwater is released more gradually than 

surface water and has no evaporative losses. In areas where groundwater is being depleted

faster than it is being recharged naturally, beaver ponds may help to offset the aquifer 

depletion, especially when beaver activity is occurring at the reach or watershed scale.

Furthermore, increased groundwater storage may help to offset rising stream temperatures 

associated with the increase in open-water surface area. Cold pockets of water have been 

found downstream of beaver dams, possibly from the upwelling of groundwater and an 

increase in hyporheic exchange (Pollock et al. 2007). This is particularly important for aquatic 

species that require cold water. For example, Weber et al. (2017) reported finding that, in 

central Oregon, maximum summer stream temperatures were reduced in stream sections 

feature a high density of beaver dams. 

Water Quality

Beaver have the ability to improve the water quality of streams by reducing suspended 

sediments in the water column, moderating stream temperatures, improving nutrient cycling, 

and removing and storing contaminants. This section highlights how beaver dams can affect 

the water quality of streams in ways that often mimic common restoration project goals.

Sediment Retention

Beaver dams affect channel form by creating ponds that increase the local water depth, reduce 

flow velocities, and dissipate stream energy. This in turn promotes sediment deposition and 

channel aggradation upstream of the dams (Naiman et al. 1986, Butler and Malanson 1995, Pollock 

et al. 2007, Green and Westbrook 2009). The size of a pond (i.e., its surface area) is often the best 

predictor of the rates and volume of sedimentation (Naiman et al. 1986, Butler and Malanson 

1995). By trapping sediment, beaver dams cause substantial changes to channel morphology.

In contrast, removing beaver dams can transform intricate, multi-threaded channels to a 

simplified single channel and increase sediment loads. For example, in a study in the East 

Kootenay region of British Colombia, Green and Westbrook (2009) found that the removal of
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beaver and their dams from 1968 to 2004 simplified channel structure and resulted in an 

estimated fivefold increase in mean flow velocity and the release of an additional 848 cubic 

yards of sediment to downstream areas.

If suspended sediment is a water quality concern, beaver colonization may be an effective 

method for reducing the amount of sediment being conveyed through the system. Beaver 

dams can influence sediment transport rates in a watershed and act as long-term sinks for 

both suspended and bedload sediments (Green and Westbrook 2009). Sedimentation rates 

behind beaver dams vary widely and typically are a function of (1) sediment availability from 

upstream, and (2) flows capable of liberating and transporting this sediment (Pollock et al. 

2014). Aggradation rates range from 1 inch to upwards of 1.6 feet per year, depending on the 

region and the interrelationships among flow, sediment characteristics, and pond geometry 

(Devito and Dillon 1993, Butler and Malanson 1995, Pollock et al. 2007). As beaver begin to 

reoccupy sites, they tend to choose dam locations that will pond large amounts of water 

(Duncan 1984) and have high sediment trapping capabilities (Ringer 1994). Allred (1980) found 

that 10 beaver ponds along the South Fork Snake River trapped 63 percent of the suspended 

sediment during peak flow. On Beaver Creek, Idaho, Reiner (1983) reported that four ponds 

trapped 78 tons of sediment in a single snowmelt period. Brayton (1984) reports that three 

years after beaver reintroduction, suspended sediment loads in Currant Creek, Wyoming, 

dropped by about 90 percent (from 33 tons per day to 3 tons per day). Pollock et al. (2007)

found that beaver dams in Bridge Creek, Oregon, collected up to 1.5 feet of sediment behind 

them during the first year they were in place. This aggradation behind the dams (including 

dams up to 6 years in age) resulted in an average reduction in slope of 1.3 percent within 

beaver-modified reaches compared to upstream reaches with no beaver dams. 

The total amount of sediment that can be stored behind beaver dams can be substantial. For

example, 22 ponds in a 620-meter stretch of Mission Creek, Washington, stored 5,847 cubic 

yards of sediment, for an average of 266 cubic yards per pond (Scheffer 1938). In Quebec, 

Canada, Naiman et al. (1986) measured retained sediment volumes that ranged from 346 cubic 

yards to 8,502 cubic yards on second- to fourth-order streams. Butler and Malanson (2005)

estimated that modern beaver ponds (i.e., after European settlement) are storing between 9.8 x 

108 and 5.0 x 109 yd3 of sediment.

The sediment retained behind beaver dams can remobilize and become available for transport 

if dams are intentionally removed, breach as a result of high flows, or are abandoned by 

beaver (see “How do beavers create their own habitat?” in Frequently Asked Questions).

However, when dams breach on small streams, most of the sediment can remain in the pond 

area (Butler and Malanson 2005). This may be due to lack of erosive flows or because the dam 

breaches only partially (i.e., there is channel avulsion around the dam), leaving most of the 

dam in place. As the water table recedes, the remaining nutrient-rich sediment in the

abandoned ponds becomes exposed and often is quickly colonized by herbaceous plants or 

shrubs, forming a beaver meadow (Ives 1942, Johnston and Naiman 1987, Westbrook et al. 2011). 

Temperature Moderation

Land use changes and ecosystem degradation already have caused summer water 

temperatures in streams and rivers to frequently exceed levels suitable for aquatic life (Kaushal 
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et al. 2010). Climate change models predict that in the near future, water temperatures will

increase even further. Maximum summer temperatures are often the single most important 

factor limiting the distribution and presence of numerous fish species in rivers (McRae and 

Edwards 1994, Wenger et al. 2011). Many salmon habitat restoration efforts in rivers and streams

focus on increasing shade by bolstering riparian areas to reduce summer peak temperatures.

In many regions, beaver dams have the ability to lower stream temperatures through the 

creation of riparian and wetland habitat. Vegetation associated with these areas offers shade 

that helps to lower stream and pond temperatures. 

A common concern about beaver dams is that they may warm streams by increasing surface 

water area and reducing the amount of shade (Reid 1952, Knudsen 1962, reviewed in Collen and 

Gibson 2000). Large ponds in general do receive more solar radiation than flowing stream 

reaches and their surface waters can warm substantially in summer. However, large, deep 

ponds (greater than six feet deep) usually stratify, with cooler water near the bottom and a 

thin layer of warm water at the surface, separated by a sharp thermocline. The cool water in 

the depths of beaver ponds can provide a temperature refuge for fish during the warm parts 

of the day, and the fish can feed in the more productive surface layers during the night and 

early morning (Hoffman and Recht 2013). Cooling downstream of dams has been reported.

Pollock et al. (2007) found that beaver dams in a stream in eastern Oregon created pockets of 

cool water downstream, presumably caused by hyporheic upwelling that resulted from the 

head differential created by the dam. The authors also found that the stream temperatures 

within the beaver dam complexes were cooler than both upstream and downstream reaches 

that lacked beaver dams (see also White and Rahel 2008; Weber et al. 2017). McRae and Edwards 

(1994) investigated how beaver dams in northern Wisconsin affected stream temperatures.

They found slight warming downstream of beaver dams; however, large ponds tended to 

dampen temperature fluctuations. They also removed several dams to assess what effect dam 

removal would have on temperature. Dam removal did not generally reduce temperatures 

and in some cases actually increased warming rates. McRae and Edwards concluded that the 

disruptive effects of dam removal on the composition of fish and invertebrate communities 

may outweigh potential direct thermal benefits. Chesney et al. (2010) found that two beaver 

dams in the Shasta River in Northern California stabilized temperatures relative to upstream 

and downstream reaches that lacked beaver dams. Small beaver ponds may not have major 

temperature effects (Hoffman and Recht 2013).

Nutrient Cycling

Although beaver are less widespread and ecologically influential today than they were in the 

past, they continue to have substantial nutrient impacts on drainage networks throughout 

many areas of North America. As Naiman et al. (1994) states, “beaver feeding strategies and 

physical alteration of the stream environment affect the hydrologic regime as well as 

community composition (McDowell and Naiman 1986, Naiman et al. 1988b, Johnston and Naiman 

1990a, b). In turn, these changes alter biogeochemical cycling and the accumulation of 

nutrients and ions in soils, sediments, and water.” 

Beaver ponds have the ability to trap and retain large amounts of material—woody and 

herbaceous vegetation and organic and inorganic soil particles—that would otherwise be 

transported downstream (Naiman et al. 1986, Naiman et al. 1994). This can easily be seen in the 
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thick accumulation of material at the bottom of beaver ponds; sometimes these accumulations 

are up to 3 feet deep. Woody debris on pond floors can be important habitat for fish, 

amphibians, and aquatic invertebrates.

Woody debris reaches the pond floor through several mechanism, including upland surface 

flows and the active process of beaver cutting down woody material for food and construction 

material, transporting it to the pond, and depositing it in food caches, dams, and lodges.

Debris also can consist of emergent vegetation produced within the pond, or forest vegetation 

that was drowned out during the original inundation of the forest by beaver. Depending on an 

individual beaver pond’s age, its ecological maturity, the channel morphology, and other 

factors related to the maintenance of system properties, the pond can act as both a net sink for 

soil and woody debris and a source of elements that are transported downstream (Naiman et al. 

1994). 

When upland and in-situ vegetation becomes trapped in beaver ponds, it creates a deep 

organic sediment layer, generally within the first decade following pond creation (Naiman et al. 

1994). Anaerobic conditions within the submerged sediment layers can lock nutrients in the 

pond sediments until high flows wash them downstream or the site is abandoned and 

drained, after which a meadow typically forms. When newly exposed sediments return to 

aerobic conditions, nutrients are released in a form that is available to vegetation, resulting in 

very productive soil conditions that catalyse rapid plant growth and diverse communities 

during initial successional stages (Naiman et al. 1994).

Contaminants

In Europe, beaver ponds have been shown to increase the self-purification capacity of small 

streams that have been polluted by communal sewage, cattle farms, and agricultural discharge

(Balodis 1994). Müller-Schwarze and Sun (2003) used a computer model to estimate the retention 

time of water flowing through a system with and without beaver dams. The model suggested 

that water flowing through a 1-square-mile area (2.59 square kilometers) with no dams resides 

for only 3 to 4 hours, while the same area with a 5-foot-high leaky dam retains water for about 

11 days. Non-leaky or tight dams hold water almost twice as long—for about 19 days.

Retention times of 6 to 8 days are sufficient to remove excess nutrients and toxins such as 

nitrogen, phosphorus, and herbicides (e.g., atrazine) from the water column (Muller-Schwarze 

2011). Removal processes include deposition, microbial decomposition, uptake by plants, and 

chemical transformation augmented by filtering. Additionally, beaver ponds can be sinks for 

fine particulate matter such as clay, which nitrogen and phosphorus can adsorb to. Thus, 

beaver ponds and associated wetlands created by dams can act as sinks for nutrients and 

toxins that would otherwise stimulate the growth of algae and other water plants and bacteria 

downstream. As one example, in the Lake Tahoe basin of California, Muskopf (2007) studied 

how removing beaver dams from Taylor Creek affected concentrations of phosphorus 

entering Lake Tahoe. The author reported that the mean total phosphorus concentrations 

downstream of the dams increased from 70.4 micrograms per liter (μg/l) (before dam 

removals) to 170.5 μg/l (after dam removals). 
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Geomorphology

The benefits of trapping and storing sediments behind beaver dams go beyond simply 

improving the water quality of streams. When beavers build dams on stream reaches, over 

long time periods the deposition of sediment behind the dams tends to raise the elevation of 

the streambed (Scheffer 1938, Butler and Malanson 1995, McCullough et al. 2005, Pollock et al. 

2007) and increase stream channel complexity by expanding riparian area (Polvi and Wohl 

2012). These changes may help prevent channel incision and maintain the hydraulic 

connection between streams and their floodplains. Channel incision—a widespread 

phenomenon in stream channels throughout the world—has caused extensive ecosystem 

degradation and is a common focus of river restoration projects. Incision can result from a 

number of different factors, including the widespread extirpation of beaver in the nineteenth

century—as well as changes in climate, land use, grazing, etc (Naiman et al. 1988b, Pollock et al. 

2014).

The effects of channel incision include lower stream bed elevations, disconnection of the 

stream from its floodplain, lower groundwater tables, loss of wetlands, decreased summer low 

flows, higher stream temperatures, less overall habitat diversity, loss of riparian areas, and 

population declines in fish and other aquatic organisms (Cluer and Thorne 2014, Pollock et al. 

2014). Recovery of incised channels can happen naturally (see Cluer and Thorne 2014), but the

process may require very long time scales. 

Pollock et al. (2014) proposed an expanded view to Cluer and Thorne’s (2014) stream 

evolution model, suggesting that the inclusion of beaver into incised streams may 

substantially reduce the recovery time, which typically ranges from decades to centuries

(Figure 2). Whether beaver can not only stop the incision process but reverse it, creating a 

positive feedback loop, depends on the quantity of sediment entering the channel and the 

channel’s ability to retain this sediment (Pollock et al. 2007) (Table 2). Beechie et al. (2008),

studied channel incision on the Walla Walla and Tucannon River basins in eastern 

Washington and estimated recovery times of 60 to 270 years without beaver and assuming 

relatively low aggradation rates (approximately 1.2 inches per year). When low densities of 

beaver dams ( 2 km-1) were included in their estimates and an estimated trapping of 224 cubic 

yards of sediment per year per dam, recovery time was reduced by 20 to 84 years—a decrease 

of up to 33 percent.

Beaver colonization in incised streams may be difficult because of the relatively deep, strong

flow, which can breach or blow out beaver dams, especially during high-flow events (Pollock 

et al. 2012). For example, along incised reaches of Bridge Creek, Oregon, most beaver dams 

were extremely short-lived; many lasted less than a year before they were washed out by 

annual spring floods or summer flash floods (Demmer and Beschta 2008). Pollock et al. (2012) 

actively assisted beaver in the construction of dams by installing different types of 
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Figure 2: Conceptual model illustrating how beaver dams affect the development of incised streams; 

(a) beaver attempting to build dams within narrow incision trenches where high stream power often 

results in blowouts or end cuts that help to widen the incision trench, as illustrated in (b), allowing an 

inset floodplain to form. The widened incision trench results in lower stream power which enables 

beaver to build wider, more stable dams (c). Because of high sediment loads, the beaver ponds rapidly 

fill up with sediment and are temporarily abandoned, but the accumulated sediment facilitates the 

growth of riparian vegetation (d). This process repeats itself until the beaver dams raise the water table 

sufficient to reconnect the stream to its former floodplain (e). Eventually (f), the stream ecosystem 

develops a high level of complexity as beaver dams, live vegetation and dead wood slow the flow of 

water and raise groundwater levels such that multithread channels are formed, often connected to 

offchannel wetlands such that the entire valley bottom is saturated, as described elsewhere (Sedell and 

Frogatt 1983, Walter and Merritts 2008). Figure from Pollock et al. 2014.
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beaver dam analogues (BDAs) and dam support structures (i.e., starter dams, post lines with 

wicker weaves, and post lines—see ”Beaver Dam Analogues” for more detail). Offering 

structural supports to possible dam sites, abandoned dams, breached dams, and existing dams

increases the chance that these structures will withstand large flow events and remain intact 

for more than one year. A two-year life span for a beaver dam is critical for beaver colony 

viability because kits typcially remain with their parents for two years before they disperse 

from the colony. Once beavers have established themselves on incised reaches, the resulting 

stable beaver colonies cause the reaches to aggrade, resulting in measurable improvements in 

riparian and stream habitat conditions (Pollock et al. 2012, Woodruff unpublished data).

Table 2. Aggradation Rates behind Beaver Dams 

Source Location Aggradation Rate (m/yr)

Butler and Malanson (1995) Glacier National Park, MT 0.02-0.28 

Meentemeyer and Butler (1999) Glacier National Park, MT ≥ 0.06

Scheffer (1938) Eastern Washington 0.55

McCullough et al. (2005) Nebraska 0.04

Pollock et al. (2007) Bridge Creek, OR 0.075 - 0.47

Reponse of Other Species to Beaver Dams

Beaver are a keystone species, meaning that they have a disproportionately large effect on 

their environment relative to their abundance. Beaver play a critical role in the watersheds of 

North America by maintaining the structure of the surrounding ecological community. Their 

presence in watersheds affects not only the types and numbers of many terrestrial and aquatic 

plant and animal species, but also maintains the change over time of channel form and the 

hydrology of watersheds. The subsections below highlight certain species that benefit from the 

habitat created by beaver.

Vegetation

How vegetation responds to habitat modifications by beaver depends on the type of 

vegetation and the region, but there are common general trends. Beaver ponds initially affect 

plants by increasing flooding. Typically, small plants within the footprint of the pond die as a 

result of the initial inundation, while trees are generally affected within the first year. As large 

trees and shrubs drown, the canopy opens, allowing more sunlight to reach the pond surface.

Increased solar energy facilitates the growth of both emergent and riparian vegetation in the 

newly enlarged riparian area that has developed as a result of creation of the beaver pond and 

the expansion of the water surface area. Riparian and emergent vegetation begin to dominate 
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where there used to be upland shrubs and trees. Overbank flooding associated with beaver 

dams may create surface flows onto floodplains, raising the local water table, which initiates 

succession toward wetland plant communities. Thus, beaver ponds can create aquatic habitat 

from many riparian, emergent, and wetland plant communities within and adjacent to ponds 

(Johnston and Naiman 1990a, Burchsted and Daniels 2014).

Increased riparian vegetation density results in the accelerated deposition of fine sediment on 

the floodplain—a result of greater flow resistance and lower velocities, as vegetation increases

roughness and pulls energy out of the water flow, reducing erosion and transport power.

Thus, beaver dams and beaver-assisted alterations in vegetation work in concert to increase 

sediment deposition.

The diversity and form of growth of riparian vegetation also are driven directly by beaver 

herbivory (Harrison and Stella 2010). Beavers consume their favorite plant species, leaving 

riparian areas dominated by non-preferred species, such as ninebark in western North 

America and red maple in eastern North America. In arid and shrub-steppe environments 

dominated by stands of willow, beaver herbivory tends to drive willow form from taller 

stands with less branching to shorter stands with more branching (Baker 2003). 

Beaver dams create habitat while they are impounding water, but they continue to create 

habitat even after colonies are abandoned, often in the form of beaver meadows, particularly 

in more mesic climates (Ives 1942, Burchsted et al. 2010, Polvi and Wohl 2012). A large flow event

can cause a dam to be breached, or it may be abandoned after a colony has depleted the 

resources in the surrounding area. After a breach some of the stored sediment is released 

downstream (Levine and Meyer 2014), but much of it is retained, depending on the local 

channel and valley form (Butler and Malanson 2005). As the water table drops in response to 

dam removal, the exposed substrate is usually colonized by vascular plants, including plants 

that germinate from the seed bank stored in the sediments (Wright et al. 2002). The resulting

newly formed “meadow” usually is devoid of trees (because the former forest was drowned 

out by the beaver pond or removed by the beaver through herbivory). After a beaver meadow 

forms, it progresses through successional stages of young and wet to old and moist (Naiman et 

al. 1994, Wright et al. 2002). The meadow may then persist on the landscape for centuries 

(Wright et al. 2002).

Beaver meadows form distinct patches on a landscape (Johnston and Naiman 1987, Terwilliger 

and Pastor 1999). The meadows act as “islands” of wetland plant communities whose 

composition differs from that of adjacent, unmodified riparian zones and upland forest 

(Wright et al. 2002). The variability in plant species composition and richness of beaver

meadows may contribute significantly to landscape-level heterogeneity.

Studies of the beaver-meadow complex have occurred almost entirely in mesic environments. 

Whether long-term beaver meadows form in more xeric regions (e.g. lower elevations in much 

of the American West) is a research question that should be pursued.

Primary Productivity and Aquatic Invertebrates

When beaver modify streams, they create excellent habitat for many aquatic insect 

populations by increasing the input and storage of organic material and sediment (reviewed in 
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Collen and Gibson 2000) and increasing primary productivity. Beaver ponds boost primary 

productivity both by increasing the availability of organic nutrients (Francis et al. 1985) and by 

allowing sunlight to reach more water surface for photosynthesis. Primary producers such as 

periphyton, planktonic algae, and aquatic vascular plants take advantage of the increased 

solar radiation. This sets the stage for the secondary producers—micro- and 

macroinvertebrates—who, in turn, take advantage of the increase in detritus—i.e., the woody 

material, decaying leaves, and decaying in-situ vegetation produced in the pond. These microand macroinvertebrates form the base of the food web that juvenile salmon and steelhead rely 

on when rearing and overwintering in beaver ponds.

Beaver ponds harbor many lentic benthic invertebrates—i.e., invertebrates that prefer slowwater habitats. Riffle reaches between ponds primarily harbour invertebrates which prefer 

faster flowing water. In comparison to streams that have no beaver activity, beaver-modified 

streams influence the community structure of aquatic invertebrates by shifting from primarily 

lotic taxa to a larger presence of lentic taxa (McDowell and Naiman 1986). Overall, having 

multiple beaver ponds in an area tends to increase the biodiversity of aquatic insect 

communities by selecting for both lotic and lentic populations. 

Fish

The pools and ponds created by beaver dams are excellent habitat for many fish species. More 

than 80 North American fishes have been documented in beaver ponds, with 48 species 

commonly using them (reviewed in Pollock et al. 2003). Because beaver ponds slow down 

stream flow and have very large edge-to-surface-area ratios, they provide considerable cover 

for fish and a productive environment for both vegetation and aquatic invertebrates that fish 

can use for food resources not found in unimpounded stream habitat (Hanson and Campbell 

1963, Keast and Fox 1990, reviewed in Pollock et al. 2003). Additionally, fish expend less energy 

foraging in the slow, productive waters of beaver ponds and side channels than they do in the 

faster flowing main channel. This leads to increases in fish abundance and size (i.e., weight 

and length); fish found in stream reaches that have beaver dams are both larger and more 

numerous than fish found in streams lacking slow water habitat. (see Gard 1961, Hanson and 

Campbell 1963, Murphy et al. 1989, Leidholt Bruner et al. 1992, Schlosser 1995, reviewed in Pollock 

et al. 2003, Sigourney et al. 2006). 

There has been extensive research on both the positive and negative effects of beaver 

modifications on fish species. Kemp et al. (2012) thoroughly reviewed the primary literature on 

this topic, focusing on North America, and completed a meta-analysis. They reported the most 

commonly cited positive and negative impacts to fish as shown in Table 3.
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Table 3. Potential Impacts of Beaver Modifications on Fish Species

Potential Positive Impacts Potential Negative Impacts

 Increased fish productivity/abundance

 Increased habitat and habitat 

heterogeneity (which promotes 

biodiversity) (Smith and Mather 2013))

 Increased rearing and overwintering 

habitat

 Enhanced growth rates

 Providing flow refuge

 Improved production of invertebrates

 Barriers to fish movement

 Siltation of spawning habitat

 Low oxygen levels in beaver ponds

 Altered temperature regime

Kemp et al. noted that many of the positive effects cited (51.5 percent) were supported by data, 

while many more of the negative impacts (71.4 percent) were speculative and not supported 

by data collected in the field. Furthermore, the most commonly cited negative impact of 

beaver dams—as barriers to fish movement—was highly speculative, as 78.4 percent of the 

studies did not support this claim with data. The authors report that 49 North American and 

European experts consider beaver to have an overall positive impact on fish populations, 

through their influence on abundance and productivity. 

Along the Pacific Coast of North America, interest in protecting beaver-modified habitat is 

growing because of the habitat’s potential to benefit anadromous fish populations. Coho 

salmon (Oncorhynchus kisutch), for example, use various types of slow-water habitat (e.g., 

sloughs and perennial and seasonal wetlands, off-channel ponds, small lakes, side channels, 

alcoves, and backwaters) as juveniles (Solazzi et al. 2000, Bramblett et al. 2002, Pollock et al. 2004, 

Ebersole et al. 2006, Henning et al. 2006) and adults; they use fast water during adult migration 

and spawning (Reeves et al. 1989). The activities of beaver can create the type of slow-water 

habitat used by coho juveniles (Swales et al. 1988, Murphy et al. 1989).

During summer, beaver ponds are important rearing grounds for juvenile coho salmon

(Leidholt-Bruner et al. 1992). For example, in the Fish Creek Basin of Northwest Oregon, Everest 

et al. (1986) found that the density of juvenile coho in beaver ponds (i.e., 1.43 per cubic meter) 

was four times higher than the density in side channels and 48 times higher than that in riffles.

Beaver ponds constituted only 2.5% of the habitat at Fish Creek but produced 50.4 percent of 

the coho salmon smolts in 1986, more than in 1985 (reviewed in Müller-Schwarze 2011).

In addition to summer rearing grounds—and possibly more critical to coho populations— is 

the use of beaver ponds and slow-water habitat as overwintering grounds. For example, 

Pollock et al. (2004) found that in the Stillaguamish River basin in Washington, the decline in 

beaver populations and subsequent loss of their dams resulted in a 61 percent reduction of 

summer coho habitat capacity and an 86 percent reduction in overwintering capacity. The 

authors conclude that the production bottleneck of coho salmon in this watershed was from a 

lack of overwintering habitat and that increasing beaver populations could be a simple and 

effective means of mitigating this loss of productivity.
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Nickelson et al. (1992) reported that, in coastal Oregon streams, beaver ponds and alcoves 

supported more juvenile coho salmon (about 1 fish per cubic meter) than did other stream

habitats, such as backwater pools, trench pools, glides, riffles, and rapids. Beaver ponds and 

alcoves represented only about 9 percent of the habitat but accounted for 66 percent of the 

coho salmon found in the system. Likewise, Bustard and Narver (1975) showed that, on 

Vancouver Island, the overwintering survival rate for juvenile coho behind beaver dams 

ranged from 61 percent to 74 percent; this was higher than the average rate for the entire 

stream systems (i.e., 35 percent). Silloway and Beesley (2011) suggested that coho salmon 

populations in the Klamath River estuary in California were limited by the availability of

juvenile overwintering sites such as coastal wetlands, beaver ponds, and alcove/slough 

habitats. Many other studies confirm the benefits of slow-water habitat on coho populations 

along the Pacific Coast (Bell et al. 2001, Brakensiek and Hankin 2007, Ransom 2007, Wallace and 

Allen 2007, Hillemeier et al. 2009, Chesney et al. 2010, Wallace 2010).

Most of the research on fish populations using beaver ponds and slow-water habitat along the 

Pacific Coast has been done on coho salmon; however, other fish species also benefit from this 

habitat. For example, juvenile Chinook salmon (O. tshawytscha) and steelhead (O. mykiss) in 

British Columbia and Washington also use off-channel and floodplain habitats for 

overwintering (Swales et al. 1988, Cunjak 1996). Pollock et al. (unpublished data) found that 

juvenile steelhead in eastern Oregon had higher densities and survival rates in beaver ponds 

than did juveniles in similar reaches without dams. Juvenile steelhead in the upper Trinity 

River of California also preferred side-channels during winter (Macedo 1992). In the 

Sacramento River system of California, juvenile Chinook show more growth and higher 

survival in floodplain habitats than do fish in mainstem habitats (Sommer et al. 2001, Sommer et 

al. 2005). Similarly, Limm and Marchetti (2009) found high growth rates in juvenile Chinook 

salmon in off-channel ponds of the Sacramento River watershed. Salmon recovery plans along 

the Pacific Coast have recently identified beaver habitat as important for salmon and steelhead

that must be protected to ensure future stocks of this important resource.

Amphibians

Beaver ponds provide important breeding habitat for some amphibians, including 

Northwestern salamanders, red-legged frogs, Pacific tree frogs, wood frogs, green frogs, 

cascades frogs, rough-skinned and red-spotted newts, and Western and American toads. By 

diversifying the landscape with different sizes and ages of ponds, beaver modified streams 

can significantly increase the biodiversity of amphibians (reviewed in Müller-Schwarze 2011). 

Red-spotted newts (Notophthalmus viridescens) readily take advantage of the unique aquatic 

habitat created by beaver activity and may actually depend on beaver ponds for their survival.

Because red-spotted newts respond to aquatic habitats that rapidly shift in time and space, 

they rapidly colonize new beaver ponds (Gill 1978). The newt’s life history seems well-tuned 

to the shifting mosaic that typifies beaver-maintained habitat (Müller-Schwarze 2011).

The wood frog (Rana sylvatica), which breeds in beaver ponds, thrives in marginal ponds with 

little inflow or outflow; these habitats are primarily found in areas saturated with beaver 

populations that are not heavily managed. For example, in the central Adirondack region of 

the northeastern United States, wood frogs living in beaver ponds had higher survival rates of 
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metamorphosed froglets and produced larger juvenile frogs than did wood frogs living in 

vernal (i.e., seasonal) pools (Karraker and Gibbs 2009). Stevens et al. (2006) suggested that older 

beaver ponds (older than 25 years) in boreal streams of west-central Alberta, Canada, 

supported more breeding wood frogs and had higher rates of juvenile growth and 

development than younger ponds (less than 10 years old). Canal networks created by beaver 

in the wetlands of Miquelon Lake in Alberta, Canada, may provide essential movement 

corridors for emigrating juvenile wood frogs (Anderson et al. 2014).

Along the West Coast, the Oregon spotted frog uses perennial wetland habitat—as well as

pools, ponds, and small floodplain wetlands associated with permanent bodies of water—

throughout its life history (Pearl and Hayes 2004, Cushman and Pearl 2007). Habitat loss has 

caused this species be become extirpated from possibly 70 to 90 percent of its historical range 

(Cushman and Pearl 2007). Its last refuge may be beaver-modified systems, which offer 

relatively favorable conditions for the Oregon spotted frog. Oregon spotted frog eggs survive 

and develop best in warm, shallow water where emergent vegetation already is established 

(Cushman and Pearl 2007). Beaver ponds’ emergent vegetation and slightly warmer surface

water (compared to upstream and downstream reaches) may provide critical habitat for this 

stage of the Oregon spotted frog life cycle. In addition, beaver dams increase the amount of 

surface water and retention times within their catchments, and this may reduce egg and 

hatchling larvae’s susceptibility to desiccation.

For more information on beaver ponds and amphibians, see Russell et al. (1999), Skelly and 

Freidenburg (2000), Quail (2001), Crisafulli et al. (2005) and Stevens et al. (2007).).

Reptiles

Beaver ponds provide important habitat to some reptiles, turtles being the most common. 

Painted turtles, western-painted turtles, western pond turtles and snapping turtles use beaver 

ponds. Other terrestrial reptiles that are found near ponds include snakes and lizards. Older 

beaver ponds seem to attract more reptiles than younger ponds, again highlighting the 

importance of the diversified landscape that beavers create over long time frames of 

occupation (Russell et al. 1999, Metts et al. 2001).

Birds

The water impounded behind beaver dams provides new habitat for waterfowl and many 

other bird species. This is not news to any avid bird watcher or waterfowl hunter who chooses 

to set up their blinds in areas colonized by beaver. Beaver-created wetlands and ponds 

produce numerous species of aquatic insects, which are essential food for hens and rearing 

broods of waterfowl. The cover offered by lush riparian vegetation— both tall trees and 

shrubs and emergent herbaceous vegetation—offers cover from predation by flying raptors 

and terrestrial hunters. Hens often choose beaver ponds to rear their broods because of the

protection that ponds offer from predators and the large supply of protein- and calcium-rich 

aquatic insects. In addition, the habitat created by beaver dams is a refuge for many migratory 

birds species, providing rest and refuelling locations along their north-south routes. The dead 

snags created by beaver through girdling and flooding provide excellent nesting habitat for 

many birds, and attracts numerous woodpecker species.
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The list of birds that actively use beaver ponds is long and varies by region. Most studies of 

beaver-modified habitat and its effect on bird populations have been on the East Coast of the 

United States. Beaver ponds in New York, for example, host American and hooded 

mergansers, Canada geese, mallards, pintails, buffleheads, wood ducks, horned and pie-billed 

grebes, great blue and green herons, kingfishers, woodpeckers, chickadees, tree swallows, 

eastern bluebirds, red-winged blackbirds, and numerous species of flycatchers and warblers.

Surveys of birds at beaver ponds across New York show that active beaver sites support more 

species of birds than do vacant or potential sites (Lochmiller 1979) and the benefit to avifauna 

persists for decades following beaver activity (Alza 2014). In the southeastern U.S. state of 

Georgia, Lochmiller (1979) found that dead snags flooded or girdled by beaver attracted more

than twice as many woodpeckers than did a tree stand without beaver. In Maine, the wetlands 

created by beaver contained flooded alder-willow thickets, herbaceous vegetation, and large 

water surfaces, all of which are essential brood-rearing habitat for the American black duck

(McCall et al. 1996). Protected beaver habitat in south-central Maine supported more mallards, 

hooded mergansers, and Canada geese than did areas where beaver trapping was allowed. 

Beaver ponds in Wisconsin attract both waterfowl and other birds, including mallards, black 

ducks, blue-winged teals, ring-necked ducks, hooded mergansers, shorebirds, swallows, 

flycatchers, hawks, warblers, sparrows, kingfishers, osprey, and bald eagles (Knudsen 1962).

Along the Continental Divide in the Rocky Mountains, birds such as the spotted sandpiper, 

Wilson’s snipe, Brewer’s blackbird, red-winged blackbirds, mallards, and green-winged teals 

all rely on beaver ponds (Brown et al. 1996). 

The beaver’s ability to create wetlands is especially important to waterfowl in the western 

United States, where riparian and wetland habitats make less than 2 percent of the landscape 

yet provide habitat for more than 80 percent of wildlife species (Hansen 1995). In addition, such 

beaver ponds may provide isolated breeding-pair ponds for waterfowl at a crucial time in 

their annual life cycle. After mating, these ponds offer the necessary protein- and calcium-rich 

invertebrates that sustain breeding pairs of birds during the egg-laying period. In a study of

beaver-modified streams in Wyoming, McKinstry et al. (2001) found that the riparian width in 

streams with beaver ponds averaged 111 feet, in contrast to 35 feet in streams without beaver.

This difference may have affected the waterfowl surveys: a total of 7.5 ducks were found per 

kilometer of stream in areas with beaver ponds, while similar areas that lacked beaver had

only 0.1 duck per kilometer of stream. When McKinstry et al. (2001) reintroduced beaver to 14 

streams throughout Wyoming, waterfowl quickly took advantage of the newly created 

wetlands and improved riparian areas.
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Chapter 2—Frequently Asked Questions

about Beaver 

Gregory Lewallen, Janine Castro, Chris Jordan and Michael M. Pollock

Where do beaver live? How do they make their dams? Why do they slap their tails? This 

section answers some of the most common questions people have about beaver biology and 

ecology.

How many species of beaver are there?

There are two extant beaver species: the North American beaver (Castor canadensis) and the 

Eurasian beaver (Castor fiber). Habitat loss and trapping extirpated both species throughout 

most of their range. The Eurasian beaver, which closely resembles its North American cousin

in both appearance and behavior, was extirpated from much of its former range by the 

beginning of the twentieth century (Halley et al. 2012), and the North American beaver soon 

followed suit. Estimates of the beaver population in North American before European 

settlement vary, but it is thought that around 55 million dam-building individuals were 

present (Pollock et al. 2003); Seton (1929) estimated the total population to be between 60 

million and 400 million. Fur trapping, which began in the 1700s to support the European 

fashion for pelt hats (Bryce 1900), resulted in a massive decline in beaver populations.

Today beaver are making a comeback—in Europe, Russia, and North America. 

Reintroductions of the species began in the United States in the early twentieth century and 

continue today. Although population numbers have not reached historical levels (current 

rough estimates put them at only 6 million to 12 million individuals (Naiman et al. 1988b), 

beaver now occupy almost all of their former range in North America. They have been so 

successful that their burgeoning populations have migrated into human-occupied territory, 

sometimes causing localized flooding or loss of vegetation. This has contributed to people’s

negative perception of the species as a pest or nuisance animal. 

Within both species of beaver, individuals manifest two very different but critically important 

behaviors: some beavers build dams to impound water and some beavers do not. This has 

bearing on river restoration projects where habitat modification through dam construction by 

beavers is intended to produce the effects needed to meet specific goals. It is of critical 

importance to understand why beavers build dams, so that we can try to predict where and 

when dam-building activity may occur (see “Why do beavers build dams?” in Frequently 

Asked Questions). The effects of colonies that do not build dams on river systems are not well 

understood and not the focus of this document. Here, we highlight how beaver dams affect

the landscape and how they can be useful in a wide range of restoration scenarios in North 

America. 

In the past, numerous subspecies of North American beaver have been identified, but 

currently, the Integrated Taxonomic Information System (www.itis.gov) does not recognize 
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any subspecies of C. canadensis. For a list of formerly recognized subspecies of C. Canadensis, 

see Table 1 in Appenix B.

What is the beaver’s range?

The North American beaver occurs throughout most of Alaska, Canada, the continental 

United States and in portions of northern Mexico (Figure 1) (Pollock et al. 2003). The beaver’s 

adaptability and ability to modify its environment to create suitable habitat has allowed it to 

thrive in a wide range of biomes. Novel evidence is challenging previously held assumptions 

about the historical range of beavers, pushing its territory to include high elevations in the 

Sierra Nevada Mountains (Lanman et al. 2012), parts of the California coast (Lanman et al. 2013), 

tidal wetlands in Washington State (Hood 2012), and peninsular Florida (Layne and Johns 1965). 

In North America, the only areas where beaver may be absent are the Arctic, the very far north 

of Canada and parts of Alaska, the dry Great Basin and desert country of Nevada and 

southern California (Jenkins 1979, Pollock et al. 2003). Otherwise, beavers are found throughout 

northern boreal forests, south to the deserts of northern Mexico, west to the Aleutian Islands, 

and all the way to the eastern seaboard.

What are important habitat elements for beaver?

Numerous studies describe detailed life history characteristics of beavers (Morgan 1868, Bradt 

1938, Jenkins and Busher 1979a, Hill 1982a, Allred 1986, Hilfiker 1991, Novak 1999, Baker and Hill 

2003, Muller-Schwarze 2011). The single most important feature of beaver habitat is the 

presence of water. Water is essential to the daily life of beavers and can be in the form of a 

stream, river, lake, or pond, as long as there is a year-round supply sufficient for access to food 

resources, protection of lodge and burrow entrances, and general safety from predators 

(Müller-Schwarze and Sun, 2003). Besides the presence of water, beaver need surrounding 

riparian areas that can provide food resources (see “What do beaver eat?”), construction 

materials, and places to build scent mounds (see ”How do beavers communicate?”). 

Are beaver just big rats?

Beavers certainly are big. They are the largest rodent in North America and second largest 

rodent in the world (after the capybara of South America) (Morgan 1868). Adult beaver 

typically weigh 35 to 71 pounds and can grow to a total length of 4 feet, including the tail 

(Jenkins and Buscher 1979, Baker and Hill 2003) (Figure 3). The tail alone is about 1.3 feet long, 

6.3 inches wide, and 0.75 inch thick. The size and weight of an individual beaver depends on

many variables, including the climate, availability and quality of food, extent and condition of 

habitat, and latitude. Mid-continent beavers, for example, can reach up to 110 pounds (Bailey 

and Balley 1927). 
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Figure 3: Photo of a North American Beaver from Southeast Alaska. Photograph courtesy of Bob 

Armstrong (Willson and Armstrong 2009).

Beaver have evolved to aquire unique features that make it well adapted for its role as both a 

keystone species and an ecosystem engineer. Baker and Hill (2003) describe the beaver’s body 

as being drop shaped, thick and heavily muscled, and supported by a large skeleton that is 

massive in proportion to other mammals of similar length. The beaver’s strong forelegs are 

shorter than its hind legs; this results in greater height at the hips than at the shoulders. The 

large head is supported by a short, thick neck almost continuous with the shoulders. The 

beaver’s stout and powerful body is perfectly suited to manipulating the surrounding 

environment by gnawing on hardwoods and carrying branches, rocks, and mud with its 

forelimbs. The skull and mandible (Figure 4) are enormous and thick so that they can

withstand the muscular force involved in chewing hardwoods such as oak and maple

(Morgan 1868). The beaver uses its four chisel-like incisors to fell trees, cut branches, and peel 

bark from stems. These teeth grow continuously. The outer enamel layer appears yellow and 

is much thicker and denser than the white inner enamel. The chiselled edge is sharpened by

grinding the upper and lower teeth together. The remaining molars—eight each in the upper 

and lower jaws—are used for grinding woody and herbaceous food (Müller-Schwarze and 

Sun 2003).
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Figure 4: Beaver skull. Beavers have massive skulls that include large incisor teeth (a) with chisel-like 

cutting edges. The molars (b) are used to crush and grind plant material. The deep groove (c) houses a 

large muscle for closing the lower mandible. The jaw joint (d) is placed high on the skull, well above the 

tooth rows, which then can meet in parallel. Figure courtesy of Bob Armstrong (Willson and Armstrong 

2009).

In adaptations to the beaver’s semiaquatic lifestyle, small round eyes and ears sit atop the 

head. Beavers can close their nostrils and ears when submerged. They have a special 

membrane that protects their eyes while underwater, and fur-lined lips that can be closed 

behind the large incisors (Jenkins and Busher 1979). Beavers also have special adaptations to 

prevent water from entering their larynx and trachea (Müller-Schwarze and Sun 2003).

One of the beaver’s most distinguishing and identifiable features is its broad, flat, scaly tail 

(Baker and Hill 2003)(Figure 16). This multipurpose appendage is used as (1) a prop when 

cutting trees and when walking on the hind legs while carrying construction materials with 

the forelimbs, (2) a rudder during swimming, (3) an alarm by slapping the water surface, (4) a 

fat reserve for lean winter months, and (5) a heat exchange organ to reduce heat losses from 25

percent in the summer to 2 percent in the winter (Marchand 1996). 

Beaver have well-developed senses of hearing and smell but relatively weak eyesight (Morgan 

1868, Novak, 1999). They are prey animals, so their eyes are widely spaced, to provide a large 

field of vision (Müller-Schwarze and Sun 2003). They use their acute sense of smell to detect 
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predators, select palatable hardwoods, and locate other beaver via mud scent mounds 

(Müller-Schwarze and Sun 2003). 

Can beavers walk on land?

The beaver’s physiology is a product of its aquatic and terrestrial lifestyles. Beaver spend most 

of their life in water but may need to move overland when cutting woody vegetation for food 

or construction materials, or when dispersing from areas to find new territory. Because of its 

body form, a beaver tends to waddle awkwardly when moving overland, but the animal can 

gallop if frightened (Jenkins and Busher 1979). Adult beavers can walk on their hind legs,

leaving their hand-like, dexterous front feet free to grasp and manipulate food, dig, and 

groom. The two inside toes of each hind foot have movable, split nails that serve as “combs” 

for preening the fur to keep it fluffy (Wilsson 1971). In the water, beaver are efficient swimmers 

who use their large webbed hind feet to propel them through the water.

Why was their fur so highly valued?

The high value placed on beaver fur pelts during the seventeenth, eighteenth, and nineteenth 

centuries is what led to the near extirpation of the animal from North America. Beaver pelts 

were used in winter clothing such as jackets and boots, but the primary use for pelts was in the 

construction of felted hats. From the 1600s through the 1800s, felt was made from the hairs of 

the under coat and shaped into a wide range of popular hat styles (Figure 5). Coloration of the 

pelt varies within and among populations, with reddish, chestnut, nearly black, and 

yellowish-brown specimens possible even within the same watershed (Baker and Hill 2003).

A beaver’s fur consists of long, coarse guard hairs that are about 10 times the diameter of the 

soft, wavy, short underfur. The guard hairs are longest (2.0 to 2.4 inches) and most dense 

along the back, but the underfur also attains its greatest length (0.8 to 1.2 inch) on the back and 

can range from a dark grey to a light chestnut in color (Baker and Hill 2003). The extremely 

dense underfur keeps the body warm and dry. With approximately 12,000 to 23,000 hairs per 

square centimeter, beavers have more hair per skin area than the South American nutria (i.e. 

8,000 to 3,000 hairs per square centimeter), but less than the river otter, which has 25,000

51,000 (Müller-Schwarze and Sun 2003). Beavers molt during the summer, so fur trappers 

prefer to harvest beaver pelts between December and March when the animals are considered 

to be in “prime condition” (Müller-Schwarze and Sun 2003). 
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Figure 5: Different styles of hats made from beaver felt. Figure copywritten by batashoemuseum.ca.

What do beaver eat?

As herbivores, beaver consume a wide variety of plant species. They eat the leaves, twigs, and

inner bark of most types of woody plants that grow near the water (Jenkins and Busher 1979).

In addition, they eat many different kinds of herbaceous plants, including grasses, sedges, and 

aquatic species such as water lilies. Their diet appears to change seasonally. During the 

summer months they primarily consume nutritious herbaceous vegetation (Chabreck 1958, 

Jenkins 1975). During fall and winter, as deciduous leaves and other aquatic vegetation become 

scarce or unavailable, they switch to primarily the inner bark (i.e., cambium) of woody shrubs 

and trees. Their digestive tracts are adjusted to this diet high in plant fiber and, through the 

help of microbial action, are able to use much of the cellulose they consume (Clarke and Hoover 
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1972, Hill 1982b, Buech 1984). Estimates of the amount of woody material a beaver eats per day 

range from 1.0 to 5.5 pounds (reviewed by Novak 1999). On the East Coast, Brenner (1962)

estimated that, during the spring and summer, individual beavers consumed about 12 ounces 

of herbaceous material per night (beaver are primarily nocturnal). 

Beavers attempt to optimize their energy returns from herbivory by using a central place 

foraging strategy and choosing smaller trees and stems (i.e., less than 3.9 inches diameter at 

breast height [DBH]). In general, they seem to choose small trees over large ones of the same 

species (Aldous 1938, Stegeman 1954, Hall 1960, Jenkins 1979, 1980, Pinkowski 1983, Belovsky 

1984). As distance from the pond increases, a beaver’s choice in tree size seems to decrease 

(Jenkins 1980). Large trees (i.e., more than 3.9 inches DBH) are sometimes felled, debarked in 

place with only the smaller branches removed, and taken back to the pond (Jenkins and 

Busher 1979). This strategy may reduce the risk of predation by limiting the amount of time 

spent on land (smaller trees take less time to fell) and reduces the amount of energy spent 

transporting material back to the pond. Large trees may also be debarked around the base and 

left standing. Barking the base of a tree can result in only small pieces of bark removed, or

most of the basal bark gnawed off. Varying the amount of barking may be a strategy to 

measure the relative nutrient value of different trees, which could explain why preferences for

certain species of tree change from year to year (Jenkins 1979). 

Beavers are able to colonize a large and diverse range of habitats throughout almost the 

entirety of North America because they can use a great number of woody and herbaceous 

species for food and construction material. (see Appendix A, see also Henker 2009 for a 

literature review of what beaver eat). Still, our understanding of beaver carrying capacity 

within a reach of stream based on food availability is somewhat primitive. Herbaceous 

vegetation taken by beaver is much harder to quantify than woody species (especially because 

beaver forage primarily at night), so scientists understand less about the impact that 

herbaceous species have on beavers’ diet, both at the individual and population levels. Some 

studies have been done to try to answer this question. For example, Collins (1976), using fecal 

samples of beavers in Wyoming, found parts of 20 species of forbs and 24 species of 

graminoids (see also Chabreck 1958, Harper 1968, Jenkins 1975, Novak 1999, Parker et al. 2007). 

Beaver need a reliable source of food, but they are choosy generalists (Harper 1969), 

consuming a wide variety of plant species. For example, Harper examined the stomach 

contents of beavers in Mississippi and found that they consumed 42 species of trees, 36 genera 

of herbaceous plants, four types of woody vines, and many species of grass (Graminae). Yet

they are “choosy” because they prefer certain species over others and will take those first if 

available. Lists of preferred plant species vary by region, and most studies of beaver herbivory 

have taken place east of the Rocky Mountains. The focus of these studies is primarily woody 

species because it is easy to identify and count beaver-chewed stems. But beavers also eat a lot 

of herbaceous material, including sedges and other emergent vegetation and the tuberous 

roots of water lilies and cattails.

In most places generalities can be made as to the food preference of beaver. Woody species 

preferred by beaver are aspen and cottonwood (Populus) and willow (Salix). These trees grow 

fast, sprout rapidly, and have soft wood that is easy to fell and peel (Müller-Schwarze and Sun 

2003). If beaver have occupied a site long enough to deplete their preferred food source, they 
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will resort to less preferred species. Diets vary depending on what is available. For example, 

Müller-Schwarze and Sun (2003) report that in New York State, after aspen and willow, 

beavers’ order of preference changes from birch, black cherry, beech, juneberry, and hornbeam 

to maples, hawthorn, and hemlock. The least preferred tree species were conifers, such as 

balsam fir, white pine, Scots pine, red pine, and Norway spruce. More recently, beaver have 

been known to take exotic species such as Japanese knotweed and kochia (Kochia scoparia) and 

salt cedar (tamarisk).

In freezing climates, what do beaver eat during the winter?

Where ponds or streams freeze during winter, beavers build food caches near their lodges or 

burrows (Jenkins and Busher 1979), which they access by swimming under the ice (Baker and 

Hill 2003). Because beaver do not hibernate or migrate during cold winter months, a reliable 

supply of food is necessary. Beavers may use the lower temperatures as a cue to start 

developing food caches during the fall, before freeze-up. Branches of deciduous species are 

gathered and embedded in the pond bottom or secured by structures such as large woody 

debris or boulders situated at the bottom. As the supply of woody vegetation accumulates in 

the cache, the material that is unsecured to the bottom becomes waterlogged and will sink.

Generally, the majority of the cache will be submerged, with only a few sticks above and on 

the surface of the water where it may freeze in the surface ice. Interestingly, beaver may also 

initiate construction of the cache by selecting large branches of less palatable species and 

floating them near the lodge. Then selections of more favoured species are brought and placed 

under this “raft,” which, over time, becomes water logged and sinks, pushing the cache down 

to the pond floor. The raft or “cap” often remains close to the surface and becomes locked in 

the ice, leaving access to the woody vegetation below to be consumed over the winter (Slough 

1978). Beavers may also supplement their winter diet of woody vegetation with water lily 

tubers and rizomes, which can be accessed from beneath the ice of the pond, but this 

component of the beaver diet is not well understood.

Beavers remain in the lodge during most of the winter, emerging periodically to swim under 

the ice, cut branches from the cache, and take them back to the relative warmth and security of 

the lodge to eat. Beavers may build multiple food caches in a single colony and not consume 

the entire cache during the winter (Baker and Hill 2003). Without a large enough cache 

gathered before freeze-up to feed the entire colony for the duration of the winter, starvation 

may occur. When surface ice is not very thick, such as in late fall and early spring, beavers 

may break the ice near the lodge and dam to allow access to food on the shore (Jenkins and 

Busher 1979). They break the ice with their front paws, stand on it until it breaks, or butt it 

with head and shoulders (Wilson 2009). In locales where water bodies remain unfrozen, beaver 

typically do not construct food caches because they can forage year-round.

How do males and females differ?

Visually, male and female beavers are indistinguishable, and, because their sexual organs are

located internally, determining a beaver’s sex in the field can be challenging. There are a 

number of different ways to ascertain their sex. The easiest field method is to locate the four 

dorsal mammary glands on females; however, this method is of limited value because the 

glands are visible only during a brief lactation period in the summer (Müller-Schwarze and 
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Sun 2003) and non-breeding females do not develop conspicuous teats. DNA markers have 

been developed, so it is possible to identify gender by collecting hair samples (Goldberg et al. 

2011). Two other methods are reliable ways to determine sex but require training and a 

sedated or constrained animal. These methods are (1) checking the color and consistency of 

anal gland secretions, and (2) palpating the baculum or penile bone (Schulte et al. 1995) (see the 

section on beaver sexing in ”Relocating Beaver”).

When do beaver begin to reproduce?

Beavers of both sexes usually reach sexual maturity and are able to produce their first litter by 

their second winter, at age 1.5 years (Larson 1967, Henry and Bookhout 1969). Regional variation 

of age at the first litter has been documented, but generally beaver can reproduce by 1.5 to 3 

years of age, although puberty may be reached several months before first breeding (Baker and 

Hill 2003, Fischer et al. 2010). Adults form relatively long-term pair-bonds. Desertion of a mate 

is rare, and usually only the death of one of the pair will result in turnover of mates (Svendsen 

1989). Breeding typically occurs in late winter and during the period of confinement to the 

winter lodge (in northern parts of the range) (Rutherford 1964). Mating occurs under water 

(Kowalski 1976) in bank dens or lodges (reviewed in Baker and Hill 2003). A gestation period 

of about 100 days is typical (Wilsson 1971), with births occurring in May through July ((MullerSchwarze and Lixing 2003). Beaver produce one litter per year, giving birth to kits in the 

security of a lodge or bank den. 

How many kits are in a litter?

The beaver litters can range in size from one to around nine kits, but the average is two to four

(Wigley et al. 1983). Litter size varies by region, with beaver in the southeastern United States 

tending to have smaller litters than beavers in the North and West (Hill 1982a, Wigley et al. 

1983). The variability in litter size may be due to the quality and quantity of habitat, severity of 

winter weather (Jenkins and Busher 1979a), or weight of the mother (Pearson 1960, Boyce 1974).

Beaver kits typically are born in late spring, fully mobile and furred (Figure 6) and weighing

about 1.1 pounds (review by Hill 1982). Lancia and Hodgdon (1983) studied kits raised in 

captivity and found that they could swim at 4 days, dive underwater in response to alarm at 8

to 10 days, and dive and stay submerged at 2 months of age. The kits initiated tail slapping in 

response to alarm when they were 3 to 4 weeks old and bipedal walking at 1 month of age.

They began carrying construction materials while walking on their hind legs at 90 days of age.

The fur of kits is not water repellent at birth, but at 3 to 4 weeks of age they begin to spread 

secretions on their fur that, by 5 to 8 weeks, creates water repellency (Baker and Hill 2003). Kits 

slowly aquire adult behaviors, hence they need a long period of rearing within a family to 

develop and hone skills required for survival after dispersal (Bloomquist and Nielsen 2010).
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Figure 6: Illustration of beaver kits in the lodge with their mother. Illustration courtesy of Katherine 

Hocker (Willson and Armstrong 2009).

How big is a typical beaver colony?

The basic social unit of beaver society is the family (Morgan 1868), often referred to as a colony.

A beaver colony is defined as “a group of beaver occupying a pond or stretch of stream, using 

a common food supply and maintaining a common dam or dams” (Bradt 1938, cited in Hill 

1982: 262). The number of individual beavers living in a colony varies depending on location, 

food abundance, habitat availability, population densities, predation pressure, and human 

activity. The average number of beavers observed living in a colony ranges from four in 

western New York (Muller-Schwarze 2011) and Alaska (Boyce 1981) to more than eight in 

Massachusetts (Brooks et al. 1980) and Nevada (Busher 1983)(Table 4).

The density of colonies varies with habitat quality and the degree to which colonization of an 

area has stabilized (Gurnell et al. 1998). It is typical for a colony on a high-quality site to have

two kits of the year, two yearlings, and a breeding pair, making for a family of about six.

However, a colony can range from a single individual up to about 10 members. Occasionally, 

2-year-old adults will stay with a family for an additional year; this occurs more frequently in 

high-density populations where unoccupied habitat is limited. Kits generally stay with the 

colony for 2 years, and dispersal of 2-year-old subadult beavers is the primary mechanism of 

population expansion (Baker and Hill 2003). Dispersal of subadults often coincides with the 

birth of kits in the spring and/or high runoff, especially where ice in winter limits movements

(Van Deelen and Pletscher 1996, Bloomquist and Nielsen 2010).
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Table 4: Average Beaver Colony Sizes Reported in the Literature

Source Location Number of Individuals

Nordstrom (1972) New Brunswick 3.2

Boyce (1974) Alaska 4.1

Easter-Pilcher (1990) Montana 4.1

Hunt and Hodgdon (1953) Maine 4.3

Müller-Schwarze and Schulte (1999) California 4.8

Payne (1982) Newfoundland 5.3

Novak (1977) Ontario 7.6

Busher et al. (1983) Nevada 8.2

Hill (1982) North America 2.7 ± 6.2 

How many beaver can live in one area?

The density of beaver populations varies both spatially and temporally, and often there are 

areas of unoccupied habitat between adjacent beaver family home ranges. Factors that 

contribute to variation in the density of beaver populations include human impacts (e.g. 

trapping), water quality, habitat suitability, area available for new colonization, length of 

habitation time relative to available resources, rapidly spreading diseases, local predation 

events, and territoriality (Baker 2003). Most important, perhaps, are abiotic factors that 

influence habitat quality, such as the stream gradient, stream size, and size of the valley 

bottom (Retzer et al. 1956, Beier and Barrett 1987b). For example, Pollock et al. (2004) studied 341 

beaver ponds in the Stillaguamish watershed in Washington State and found that 90 percent

of the ponds were in low-gradient streams in unconfined valleys. Similarly, (Suzuki and 

McComb 1998) studied 170 beaver dams in Oregon’s Drift Creek basin and found that only 10

percent of the dams were on streams with gradients higher than 6 percent. After all the 

preferred habitat has been occupied, predation pressure can affect beaver population densities 

(see Boyce 1981). 

Beaver density typically is calculated as the number of colonies per unit length of stream times

the number of beavers in each colony (Table 5 and 6). Population estimates, on the other hand, 

can be derived using aerial counts of lodges or food caches multiplied by mean colony size 

(Hay 1958, Bergerud and Miller 1977, Peterson and Payne 1986). This method assumes spatial and 

temporal consistency of colony size; however, Swenson et al. (1983) found this assumption to be 

invalid, reporting that estimates did not correlate well with population size because mean 
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colony size changed between years and across areas. Swenson et al. (1983) noted that the size 

and composition of colonies must be estimated periodically to provide the necessary 

information to detect temporal changes in beaver populations (McTaggart and Nelson 2003).

Potential methods of assessing the size and composition of individual colonies include

removal trapping, mark-and-release live trapping, and nocturnal censuses conducted using 

night-vision binoculars.

Table 5: Beaver Colony Densities Reported In The Literature.

Source Location Colony Density 

McCall et al. (1996) Maine 0.32 km-2

Boyce (1983) Alaska 0.63 km-1

Beier and Barrett (1987b) California 0.74 km-1

Howard and Larson (1985) Massachusetts 0.83 km-1

Collins (1976) Wyoming 0.90 km-1

Nordstrom (1972) New Brunswick 1.25 km-1

Johnston and Naiman (1987) Minnesota 1.00 km-2

Hill (1976) Alabama 1.9 km-1

How fast can colonies grow?

Beaver populations in areas at or near carrying capacity typically change relatively slowly 

over time. Conversely, in areas with unexploited preferred habitat, populations can rapidly 

increase and expand over the landscape. The size of an unexploited beaver population 

(meaning one with little to no predation pressure, including human trapping) is limited by the 

amount of suitable habitat and resources within that range.

For example, on the Kabetogama Peninsula of Voyageurs National Park in Minnesota, several 

studies have looked at the effects of an increasing beaver population on the landscape with 

few predators and excellent beaver habitat (Johnston and Naiman 1990b, a, Pastor et al. 1993). 

Using aerial photographs from 1940 to 1986 and beaver population data from 1958 to 1986 

(Naiman et al. 1988b) showed that the number of beaver dams increased from 71 (many of 

which were abandoned) in 1940 to 835 by 1986. Beaver population growth rates remained 

fairly steady over that time, with approximately nine colonies added each year (Johnston and

Naiman 1990a). This was an increase from near extirpation of beaver on this landscape to a 

density of about one colony per square kilometer in a little more than 4 decades.

Another example of expanding beaver populations is in Allegany State Park, New York. Here

Müller-Schwarze and Sun (2003) note how a single pair of beaver were introduced to the park 
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in 1937 after trappers had removed all the beavers by the start of the twentieth century. A year 

later two families were living within the park. By the 1950s beaver occupied all of the suitable 

habitat within the park, and by 1973 there were 34 beaver colonies in the park. Currently, 40 to 

60 families occupy the park and the population seems to have stabilized, presumably because 

suitable habitat and food resources have become limiting.

Beaver populations undergo stages of growth and decline as populations increase, occupy 

more territory, and deplete resources in the area. Busher (1987) studied a beaver population in 

California that illustrates this typical change over time. Originally, beaver occupied 20 percent

of suitable stream habitat. Within 25 years, the population expanded to occupy 56 percent of 

the suitable habitat, increasing the number of beavers per kilometer of stream from 1.57 to 

4.00. However, fluctuations in the beaver population occurred during this time of overall 

expansion. Initially the population stabilized at around 3.38 individuals per kilometer and 

then declined. This was followed by two more population expansions, eventually reaching a

high of four beavers per kilometer.

What are lodges?

Lodges are structures that beaver create to protect themselves from predators and weather. As 

Morgan (1868) observed, beaver dig burrows and construct lodges, “both of which are 

indispensable to his security and happiness.” Typically, lodges are composed primarily of 

sticks and branches piled into a large mound. Large rocks may be used as foundational or 

anchoring material, with herbaceous material used as sealant and filler. The top of the lodge 

generally is left unsealed to allow for ventilation (Novak 1999). If woody material is scarce, 

beavers may construct lodges primarily with non-woody material (Dennington and Johnson 

1974)(Figure 7). The interior of the lodge typically contains a nesting area that is situated a few 

inches above the water line so that it remains dry (Grinnell et al. 1937) and often is lined with 

grasses or other herbaceous material (Morgan 1868). Well-built lodges can have considerable 

insulating capabilities. For example, Miller (1967) found that the lowest inside temperature for 

a water lodge in Alaska was 25 degrees Fahrenheit when the outside air temperature was -49 

Fahrenheit. For more studies on lodge air temperatures see Stephenson (1969), and Novak 

and Cook (1972).
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Figure 7: Beaver lodge constructed with primarily mud and herbaceous material in a site dominated 

by reed canary grass.

How many types of lodges do beavers build? What are bank burrows?

Lodges come in three general types: bank burrows, bank lodges, and water lodges. The 

entrances of all three types are continually submerged by water, to protect the beaver from 

predators. 

Bank burrows are constructed in the bank of a river, lake, pond, or canal and are often dug 

under a large tree or shrub that provides support to the walls and roof of the den (Morgan 

1868). The entrance is dug out below the water level, a nest area is created above the water 

line, and small holes are dug in the surface soil to ventilate the den (Gurnell 1998). Where 

beavers live exclusively in large rivers or deep lakes, bank dens typically are the only housing 

structures they build (Baker and Hill 2003). Even in areas where beaver eventually build dams 

and lodges, bank dens often are used while the lodge is being constructed and at times after its 

completion (Baker and Hill 2003). Beavers do not build bank burrows in areas where the 

substrate limits their construction (i.e., in very rocky soils or permafrost) or where the bank is 

not high enough to allow the nest chamber to remain above the water line (Gurnell 1998). In 

the latter case, beavers build intermediate structures between burrows and water lodges, 

called bank lodges (Gurnell 1998). 

Bank lodges are essentially burrows where beaver have piled woody material and mud above 

the nest chamber on the bank and dug a hole through the soil surface to create a nest chamber 

(Gurnell 1998) (Figure 8). The nest chamber in a bank lodge may by located beneath the 

ground surface or on top of the hard ground, with sticks and mud piled above (Morgan 1868). 
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If dam height and water level increase, construction of the bank lodge may continue, 

sometimes for years (Baker and Hill 2003).

Figure 8: Bank lodge situated on the shores of a lake in Southeast Alaska. Photo courtesy of Bob 

Armstrong (Willson and Armstrong 2009).

Water lodges, which are situated in a lake or pond, are completely surrounded by water 

(Figure 9). Generally, lodges have two or more underwater entrances and a nest area situated 

above the water line (Grinnell et al. 1937). Fluctuating water levels can stimulate lodgebuilding activity (Novak 1999).

In many areas a combination of lodges and bank burrows are used by all or different members 

of the colony (Baker and Hill 2003). Looking at both species of beaver, researchers in Russia 

found that about 75 percent of beaver used water lodges and bank lodges, while the rest lived 

in bank burrows (Danilov and Kanshiev 1983).
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Figure 9: Large beaver lodge completely surrounded by water in Southeast Alaska. Photo courtesy of 

Bob Armstrong (Willson and Armstrong 2009).

Why do beavers build dams? 

Beavers build dams to raise water levels. Higher water levels provide the following benefits

(among others):

 Allowing beavers to dive to safety from predators

 Increasing foraging area and providing safe and easy travel routes to and from feeding 

areas

 Allowing logs and branches to float within the pond 

 Ensuring that the entrances to lodges and burrows remain underwater, so as to protect

beaver from land-based predators such as coyotes, cougars, wolves, and bears

 In colder climates, keeping ponds at a sufficient depth to maintain liquid water under a 

sheet of ice during the winter months

Without sufficiently deep water in their habitat, beaver may be more susceptible to predation 

and have to expend more energy to collect food resources by moving overland. To ensure a 
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constant water level, beaver construct dams, with building activity being timed according to 

necessary adjustments in water level (Richard 1983). The sound of running water can stimulate 

beavers to initiate dam building or perform dam maintenance (Wilsson 1971). Sometimes 

several dams are constructed and maintained by the same colony to control ponded water in 

relation to lodge or burrow entrances (Gurnell 1998). 

Typically beavers build multiple dams in succession over a relatively small reach of stream,

creating a stair-step valley and stream profile (Morgan 1868). This series of dams, or beaver 

dam complex, consists of flat, ponded areas with abrupt gradient changes at each dam site 

(Pollock et al. 2003). Over long periods of time, beaver dams can accumulate significant 

sediment behind them, thus effectively changing the longitudinal profile of the valley slopes 

over long distances (Ives 1942, Westbrook et al. 2010, Polvi and Wohl 2012). Multiple dams in a 

series also help dissipate the energy of large flood events and may act as an insurance policy 

against dam failure: if one dam breaches, others are still in place. Furthermore, having 

multiple dams increases the amount of retained water, which increases the foraging area of the 

colony and encourages the growth of woody vegetation and herbaceous species used for both

food and construction materials. Thus, beaver dam building activity can create a positive 

feedback loop.

How are beaver dams constructed?

Beavers are unique in their ability to construct impressively large structures located in 

dynamic aquatic systems where substantial amounts of water (Naiman et al. 1988b, Johnston and 

Naiman 1990a, Hood and Bayley 2008) and sediment can be impounded behind them (Butler and 

Malanson 1995, Pollock et al. 2003, Walter and Merritts 2008). Dam construction is initiated by 

pushing sediment, rocks, or sticks so that they form a ridge perpendicular to the flow of 

moving water, or by locating sites to take advantage of existing substrate (Lancia and Hodgdon 

1983) or existing structures, such as abandoned breached dams or large woody debris 

(MacCracken et al. 2005). Structure is added by anchoring leafy branches, peeled branches, or 

other material to the substrate, which can be the stream bottom, stream banks, large rocks, or 

coarse woody debris. Branches in the bulk of the dam are intertwined perpendicular or 

parallel to the stream. In addition, branches are often placed on the downstream side of the 

dam, parallel to the stream, with the cut end placed into the substrate and the branched end 

pointed upstream; this adds structural support to the dam and helps prevent the development 

of a downstream scour pool.

Dam-building behavior has been well documented and described in the literature (Morgan 

1868, Hilfiker 1991, Gurnell 1998). Baker and Hill (2003) reviewed this information and 

reported that dams typically consist of tree trunks, branches, twigs, bark, leaves, earth, mud,

and sometimes stones (Gurnell 1998), but a wide range of material can be used. Dams can 

include conifers, sagebrush, tamarisk, aquatic plants, corncobs, cornstalks, plastic, metal, or 

other debris. Beavers sometimes peel and eat the bark of branches before adding the stems to 

the dam. When preferred woody food species are limited in the area, beavers will select less 

preferred species to use as construction material (Barnes and Mallik 1997a).

Once the woody material is in place, beavers seal the dam by adding mud and herbaceous 

material such as grass and leaves, especially on the upstream dam face. Mud is typically 
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gathered from the stream bottom upstream of the dam and packed into the dam with their 

forelimbs. Typically, dams are maintained through repairs and additions (or removal of 

debris) to both the height and length to control water levels. In colder climates, dam 

construction activity is highest in the fall before freeze-up and in the spring to repair damage 

from high flows. In ice-free climates, construction activity may occur year round, with less 

activity during the summer months. 

How big are the dams?

The size and number of dams in a colony and the amount of water retained in the ponds vary 

greatly, depending on factors such as duration of occupancy, topography, substrate, flow 

levels, and available vegetation (Gurnell 1998). Dams may begin as small structures that span 

the channel only partially but can evolve through time, progressively extending until they

eventually span the entire channel. Dams range in size from small canal- or culvert-spanning 

structures approximately 20 inches long to an incredible 930 yards long in a recent example in 

Wood Buffalo National Park in Alberta, Canada. The height and width of beaver dams also 

vary in size. Dams range between 8 inches to 6 feet in height and 3 to 6 feet in width (Baker 

1995). 

As food sources are depleted or the water regime adjusts seasonally, additions to dams may 

extend further onto floodplains, until they eventually spans the entire valley width (Gurnell 

1998). As water collects behind dams and spreads laterally from the primary channel, the 

beavers may build small check dams on the floodplain to further impound and direct the flow 

of water (Baker and Hill 2003). This illustrates how beavers may develop dams and ponds up 

on the floodplain, even though the width of the dammed channel is relatively small (Gurnell 

1998). As the beaver colony grows in size, additional dams may be constructed throughout the

colony’s territory. The area of inundation generally increases over the first few years of 

occupation (Naiman et al. 1988, Johnston and Naiman 1990a). Over time dams eventually breach, 

possibly as a result of abandonment, high-flow events, or both. Breached dams often remain in 

place and may be used as a starting point for new dams when beavers attempt to reoccupy 

formerly used territory. Breached dams that remain in place, partially spanning the channel,

can add heterogeneity and complexity to the stream system, providing additional areas of

slow water, riffles, and riparian habitat (John and Klein 2004, Burchsted et al. 2010, Polvi and 

Wohl 2012, Pollock et al. 2014).

Do Beaver dams block fish passage?

A common concern regarding beaver-modified habitat is that their dams block the movement 

of fish, in particular salmon and steelhead. However, this claim is largely unsupported by the 

literature. Rather, the literature suggests that at most, beaver dams may act as temporary 

barriers to adult fish passage, typically during low-flow periods. As flows increase, dams 

typically become more easily passable by both juvenile and adult fish, with a diversity of flow 

paths over, through, under, and around these semi-permeable structures (Schlosser 1995, 

Pollock et al. 2014)(Lokteff et al. 2013). Moreover, these flow paths continually change with 

beaver maintenance, construction, and abandonment and with fluctuations in discharge 

(Lokteff et al. 2013). 
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Most recent research suggests that the increased complexity of habitat created by beaver dams 

is beneficial to many fish species (Collen and Gibson 2000, Schlosser and Kallemeyn 2000, Pollock 

et al. 2003, Pollock et al. 2004, Kemp et al. 2010, Kemp et al. 2012, Pollock et al. 2012; Bouwes et al. 

2016). Dams might even provide a competitive advantage to certain native fish species relative 

to non-natives (Lokteff et al. 2013). This is reasonable because salmon, steelhead, and many 

other fish species are found throughout the range of the North American beaver and have 

cohabitated streams together with beaver since the last ice age. At times when low flows 

temporarily may inhibit non-native (e.g. bass) fish movement across beaver dams, species of 

native fish, most notably salmonids, are able to jump sufficient heights and lengths to clear the 

dams (Powers and Orsborn 1985). Although not well documented, observations suggest that, 

rather than leaping over dams, juvenile and adult species of salmon (i.e. coho, sockeye, and 

steelhead) pass beaver dams by swimming around the dam, either accessing the numerous 

small, low-velocity flow paths that are present in most dams or swimming over the wet 

portions of the dam face and into the upstream pool. Such behavior can also be inferred from 

observations of migrating juvenile coho salmon into upstream overwintering ponds, the 

movement of juvenile coho salmon between beaver ponds and downstream tributary habitat, 

and the spawning of adult coho salmon and other salmonids in stream reaches above beaver 

dams (Bryant 1983, Everest et al. 1986, Murphy et al. 1989, Olsen and Hubert 1994, Solazzi et al. 

2000, Roni et al. 2006, Rosenfeld et al. 2008). 

Lokteff et al. (2013) studied the effects of beaver dams on the movement of one native trout 

species (Oncorhynchus clarkia) and two non-native species (Salmo trutta and Salvelinus fontinalis) 

in two northern Utah streams. The authors found that all three species were able to pass 

through beaver dams, but the native trout passed dams more frequently than either of the 

non-native species. Spawn timing and the physical characteristics of the dams affected the 

passage of each species. In Bridge Creek—a tributary of the John Day River in Oregon—

Pollock et al. (2012 and unpublished data) and Bouwes et al. (2016) documented both juvenile 

and adult steelhead throughout four treatment reaches of a stream that had more than 100 

beaver dam analogues (see ”Beaver Dam Analogues”) and reinforced beaver dams, including 

upstream of all the structures. Studies of the effects of beaver dams on Atlantic salmon also 

show that movement was affected by flow rates. In years with low flow, redd counts above 

dams were depressed, but with the return of high flows, access to upstream reaches and red 

counts generally increased (Mitchell and Cunjak 2007, Taylor et al. 2010). This suggests that any 

detrimental effects of beaver dams on the population as a whole were negligible. 

Further research is needed to clarify this common misconception that beaver dams block fish 

passage. For example, Kemp et al. (2012) reviewed 108 studies evaluating the effects of beaver 

dams on fish and fish habitat. A total of 43 percent of the studies cited beaver dams as 

“barriers to fish movement.” However, the authors found this negative effect of dams to be 

largely speculative, since 78 percent of those studies did not support this claim with data. 

Kemp et al. (2012) conclude that negative effects of beaver dams on fish movement at most are 

short-lived and localized, and have negligible long-term impacts.

Do beaver dams increase stream temperatures?

In some regions, high stream temperature can be detrimental to salmon and other aquatic 

species. Beaver dams may increase stream temperature by removing riparian shade and 
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increasing water surface area and they may also lower stream temperatures by increasing 

groundwater (hyporheic) exchange, creating deep pools, and increasing shade from riparian 

vegetation (Pollock et al 2007; Weber et al. 2017). The effect of beaver dams on stream 

temperature largely depends on pre-existing conditions. For example, construction of a beaver 

dam in a shallow, wide stream is likely to reduce average water temperatures because the 

greater “thermal” mass of the larger water volume will dampen temperature fluctuations, 

while the decrease in the surface to volume ratio will reduce the amount of insolation per unit 

mass of water. While dam construction across the floodplain on a deep, narrow stream is 

likely to increase average temperatures because the surface area per unit volume will increase. 

Similarly, where there is the potential for good hyporheic exchange, beaver dam construction 

can lower stream temperatures; this happens because water flowing through alluvium rapidly 

exchanges heat and equilibrates to the temperature of the substrate through which it is 

flowing. Conversely, during the winter, hyporheic exchange can warm water if the ground is 

warmer that the temperature of the stream surface water (e.g. see Chesney et al. 2010)

Beaver can both reduce and increase the amount of riparian vegetation and this can also affect 

stream temperature. When beaver initially occupy a site, they often cut down stream-adjacent 

trees and this can reduce shade and increase stream temperatures. Over time, emergent 

vegetation can grow and provide shade. In more arid environments, and particularly in 

incised streams where there is little to no riparian vegetation, beaver dams can raise water 

tables and expand the extent of riparian vegetation and this can increase the amount of shade 

relative to pre-dam conditions (e.g. see Pollock et al. 2007).

Whether changes in stream temperature are “good” or “bad” depends on the metabolic 

optimal temperature range of the species in question and, for fish such as salmon and 

steelhead, the availability of food resources. For example, warmer than average temperatures 

for the area combined with abundant food supplies can lead to rapid growth of certain coldwater species, such as steelhead and Chinook salmon. In northern latitudes such as in Alaska, 

a slight increase in water temperature such as that associated with beaver ponds (i.e., from 2 to 

4 degrees) may increase the length and weight of rearing juvenile salmon (Willson and 

Armstrong 2009). Beaver modifications may increase thermal complexity due to the creation of 

deep-water habitats that stratify giving mobile fish more thermal options to choose from. 

Experimental removal of beaver dams to reduce temperature suggests that the physical 

habitat effects of dam removal are far more detrimental to aquatic habitat than the likely 

change in temperature (McRae and Edwards 1994).

What are beaver canals?

Once a dam is constructed and a pond develops behind it in a low-gradient area, the zone of 

floodplain that is accessible to the beavers can be further enlarged through the construction of 

canals (Gurnell 1998). The length and width of a beaver canal varies (i.e., 3 to 300 feet long and

14 to 40 inches wide), and typically they are more than 20 inches deep (Gurnell 1998). Beaver 

use canals as travel corridors to access new foraging habitat and also to transport woody 

vegetation to the beaver pond (Gurnell, 1998). As beaver collect and transport food and 

construction materials from the adjacent uplands back to the pond, they start to create surface 

trails or “slides.” These trails make it easier to drag food and construction materials across the 
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ground and extend their foraging areas (Baker and Hill 2003). Eventually, slides may be dug 

out, extending or converting them into canals and expanding the beavers’ foraging range from 

the pond. 

How do beaver communicate?

Beaver communicate through scent, vocal sounds, tail slapping and body movements. The 

highly social nature of beaver requires complex communication between family members 

within single colonies and between separate colonies within watersheds. These different types 

of communication are discussed below.

What is castoreum?

Communication by scent is facilitated through two functional scent organs: the castor sacs and 

anal glands (Walro 1980). Urine is concentrated in the castor sacs, where it becomes castoreum, 

a strong-smelling brown paste (Baker and Hill 2003). It is likely that, as the beavers’ diet 

changes throughout the seasons, the castoreum changes in chemical composition and odor.

The scent of castoreum can elicit various behavioral responses from beavers, although 

territorial defense probably is the primary one. For example, Müller-Schwarze (2011) 

deposited castoreum chemical compounds within a beaver colony’s territory. The resident 

beavers investigated these odors and often destroyed the marks and “overmarked” them.

Butler and Butler (1979) proposed that castoreum is used by beaver to provide information 

about individuals and physiological status within a family. Svendsen (1980) proposed that,

beyond simply being used as a territorial marker, castoreum deposited on scent mounds (see 

”What are scent mounds?”) enhances the confidence of resident beavers and lowers that of 

intruders at the same time. Schulte (1998) showed how beaver can use castoreum to 

distinguish family members from non-members and neighbors from complete strangers.

Although more research is needed to confirm these results and hypotheses, it is clear that 

beaver castoreum scent communicates more than just territorial occupancy. 

What are scent mounds?

Both castoreum and anal gland secretions are used in scent marking and are actively 

deposited on “scent mounds” that consist of piles of mud and debris (Dugmore 1914, Hay 1958, 

Schramm 1968, Wilsson 1971, Butler and Butler 1979, Bollinger 1980, Müller-Schwarze and Heckman 

1980, Walro 1980, Lancia and Hodgdon 1983, Muller-Schwarze et al. 1983). Most scent mounds are 

constructed by adult males who use their forelimbs to gather mud, sticks, leaves, and other 

materials from the bottom of the pond, carry the debris to a selected location in a bipedal 

fashion, and pile the debris into mounds near the shore (Figure 10). A mud pile can consist of 

a single “load” or measure up to 2.5 feet (80 centimeters) in diameter and 20 inches (50

centimeters) high (Müller-Schwarze 2011). The beaver deposits secretions on the scent mounds 

both during and after construction. Beavers of all ages anoint the mounds with scent, but the 

frequency of marking increases with age (Baker and Hill 2003, Müller-Schwarze 2011). Males 

of all ages place the most scent marks (Lancia and Hodgdon 1983) . Large numbers of scent 

mounds—more than 100—can be constructed within a territory, and they are usually placed 

on or near lodges, dams, and trails near the water’s edge (Baker and Hill 2003). Beavers

deposit scent marks on mounds to elevate the point of odor release. The moist mud helps 
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intensify the odor, and the mound protects the raised odor beacon from becoming inundated 

as water levels fluctuate (Müller-Schwarze 2011). 

Figure 10: Scent mounds piled near the shore of Dredge Creek in southeast Alaska near the 

Mendenhall glacier. Mary Willson pictured in the foreground. Photo courtesy of Chuck Caldwell.

Beavers build most of their scent mounds in the spring, as 2-year-olds disperse from their 

home colonies to colonize new areas (Hodgdon 1978, Svendsen 1980). Marking of the scent 

mounds sometimes continues year round in warmer, ice-free, climates, but generally it abates 

in the summer and fall, when invasion pressure has declined (Müller-Schwarze 2011). To 

maximize the efficacy of mounds, beavers place them in strategic locations, such as near the 

paths most likely used by invading beaver (Müller-Schwarze 2011).

Do beaver vocalize?

In addition to communicating by scent, beaver use a rich repertoire of vocalizations 

(Novakowski 1969, Pilleri 1983). Adult beaver have been known to produce burps, whines, 

hisses, and gnawing and chewing sounds. Hissing is probably the most common vocalization.

Beavers hiss in defense when confronted with other animals or to defend their territory

(Leighton 1932, 1933, Muller-Schwarze 2011). Young beaver are particularly vocal (Hodgdon 

1978). They often produce a soft repetitive whine, apparently to solicit food from other beavers 

in the family, or when placed in uncomfortable situations such as being forcibly expelled from 

the lodge and into the water (Müller-Schwarze 2011).

Why do beaver slap their tails?

The best-known alarm signal of beavers is the tail slap. In response to any disturbance at or 

near the pond, beavers first attempt to investigate the source. If they are sufficiently startled, 

they immediately slap their tail on the water surface with a powerful stroke, creating a loud 

“slap” sound, and dive away (Müller-Schwarze 2011). Tail slapping may serve as a warning 

signal to family members, who typically respond by returning to the pond (if foraging on 
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land), diving away, or returning to the lodge (especially kits). Tail slapping also may be used 

to drive away predators or ungulates looking to forage on the beaver’s food cache, and to elicit 

a response from the source of disturbance (Brady and Svendsen 1981, Lancia and Hodgdon 1983).

Beaver seem to discriminate among tail slaps from different individuals. Tail slaps by adults—

most notably adult females—elicit the most response by all age classes and sexes (Lancia and 

Hodgdon 1983). In contrast, older beaver often ignore tail slaps by juveniles, whose slaps sound 

different because of the size and shape of their tail (Müller-Schwarze 2011). It may be that 

young beavers learn the “social rules” of appropriate use of the tail slap over time.

How do beaver create their own habitat? 

Beavers are ecological engineers that create and maintain habitat to better suit their needs for 

survival. They do this primarily through their unique behavior of constructing dams on the 

landscape. Beaver dams can dramatically increase the amount of impounded water (Johnston 

and Naiman 1990a) and sediment behind them (Naiman et al. 1986, Butler and Malanson 2005,

Green and Westbrook 2009), increase riparian vegetation (Pollock et al. 2007), expand 

wetlands (Hood and Bayley 2008), increase floodplain connectivity (Naiman et al. 1988,

Pollock et al. 2003, Westbrook et al. 2006), and change and enhance biological diversity 

(Schlosser and Kallemeyn 2000, Muller-Schwarze 2011). At the landscape scale, beaver can alter 

the hydrology, geomorphology and plant and animal community structures of watersheds 

(see Naiman et al. 1988, Pollock et al. 2003, Müller-Schwarze 2011, Pollock et al. 2014). 

These aquatic habitat modifications are a successional process on the landscape, varying both 

temporally and spatially, that creates a shifting mosaic of environmental conditions (Johnston 

and Naiman 1987, Naiman et al. 1988b, Johnston and Naiman 1990a, Pastor et al. 1993, Johnston 1995, 

Snodgrass 1997, Schlosser 1998, Schlosser et al. 1998, Snodgrass and Meffe 1998). Beavers create 

dynamic patches on the landscape that change over time as stream reaches are colonized, 

flooded, and eventually abandoned (Schlosser and Kallemeyn 2000). The dynamics of these 

changes result in a mosaic of aquatic patches that vary in age across the landscape; types of 

patches include ponds, collapsed ponds, streams, and beaver meadows (Naiman et al. 1988b, 

Wright et al. 2004).

Once beavers are established in an area, population expansion may cause their food supplies 

to become limited. As beaver impound water, it expands onto the floodplain, increases local 

aquifer recharge, and raises water tables. The increase in saturated soils creates larger areas of 

wetlands and riparian zones, which facilitate the growth of emergent vegetation and 

herbaceous vascular plants used for food. The increase in deep water facilitates beaver’s access 

to woody vegetation that can be also used as construction material to build more dams. With 

more food resources and suitable habitat increasing, the number of beavers that a given area 

can support also increases. Thus, once established, beaver tend to create a positive feedback 

loop that improves their own food supply, enabling more dams to be constructed and further 

increasing food availability (Pollock et al. 2007, 2014).
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Chapter 3—Beaver Myth Busters

Gregory Lewallen

Today we know a lot about beavers. Yet people still repeat a number of poorly substantiated 

assertions (i.e., myths) about beaver and beaver dams. In this section we discuss, and dispel

myths and rumors surrounding this storied creature.

Myth: Beaver always live in streams.

Headwater and low-gradient streams are well-known beaver habitat, but beavers are 

opportunistic and commonly use a wide variety of available habitat, including lakes, side 

channels, estuaries, large rivers, and tidal channels (Hood 2012) (Figure 8), as well as artificial 

features such as ditches, canals, ponds, and reservoirs. As long as there is a food supply and 

either the existence of—or the ability to build—deep, slow-water habitat that reduces 

predation and keeps lodge entrances submerged, there is potential for beaver occupation

(Müller-Schwarze 2011) (Figure 7).

Myth: Beaver eat fish.

Beavers have never been observed eating live fish. Beavers are considered choosy generalist 

herbivores (Harper 1969) (see “What do beavers eat?” in Frequently Asked Questions). Beavers

are morphologically and physiologically adapted to feeding on woody and herbaceous 

material; for example, they have unique microflora in their digestive tract that allow them to 

digest cellulose (Jenkins and Busher, 1979, Novak 1987). Unlike the river otter, which eat 

primarily fish, beaver do not have the speed, maneuverability, sharp teeth, or claws necessary 

to catch fish. Beaver ponds can be excellent habitat for fish, especially summer and winter 

rearing grounds for juvenile salmonids. Although they directly increase the quantity and 

quality of fish habitat, beaver themselves do not prey on fish. 

Gleason et al. (2005) reported observing three beaver feeding on Chinook salmon carcasses that 

had been discarded after being filleted by anglers along a relatively deep-water pool of 

Montana Creek in Alaska’s Susitna River drainage. The authors hypothesized that beaver in 

Alaska, and presumably elsewhere in the Pacific Northwest, engage in this feeding behavior 

to take advantage of the readily available and predictable source of protein and fat, at least on 

a seasonal basis.

Myth: Beaver ponds are a source of fine sediment.

Beaver ponds have the ability to retain significant amounts of fine sediments. However, 

sedimentation rates behind beaver dams vary widely (Pollock et al. 2003). Naiman et al. (1986) 

found that beaver dams in a boreal forest ecosystem stored between 46 and 8,502 cubic yards

of sediment. Butler and Malanson (1995) studied sediment deposition behind beaver dams in 

Montana and found that younger ponds averaged 73 cubic yards of sediment, while older 

ponds averaged 266 cubic yards. Butler and Manlanson (2005) estimate the total amount of

sediment stored behind beaver dams in pre-European settlement of North America from 9.81
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billion cubic yards to an astounding 163.5 billion cubic yards of sediment. Factors that 

influence sedimentation rates include the growth rates of the emergent vegetation found in the 

ponds, upstream sediment loads, the number of beaver dams upstream, and the frequency of 

dam failures (Pollock et al. 2003). For more information on sedimentation accumulation 

behind beaver dams, see “Sediment Retention” and “Geomorphology” in Section 2.

The sediment stored behind beaver dams has the potential to be a source of fine sediment for 

downstream reaches of streams and rivers after dams are abandoned or breached. However, 

the amount of sediment evacuated downstream beyond a breached dam is typically small 

(Butler and Malanson 2005), and dam breaching generally occurs during high-flow events.

Much of the sediment stored by beaver dams is retained by emergent vegetation that colonizes 

the bare surfaces of the accumulated sediment, although Butler and Malanson (2005) do 

present rare examples of catastrophic events resulting from beaver dam failure.

Myth: Beaver always build dams.

Beavers do not always build dams. They construct dams to impound water in low-gradient 

areas and to create ponds when needed. The pond is used to dive to safety from predators, 

increase their foraging area, transport food resources, and control water levels so that burrow 

and lodge entrances remain submerged at all times. In northern latitudes and at high 

elevations where streams freeze, the pond must be deep enough to remain ice free below the 

surface, so that beaver can access food resources stored under the ice in caches.

In areas where these conditions are already met, such as lakes or large rivers, beaver do not

build dams. Instead, they dig bank burrows, bank lodges, or lodges for habitation. They may 

also build canals to increase their foraging area. Mixed populations of beaver, some of which 

build dams and some of which do not, have been observed in smaller streams, suggesting that 

the non-dam building strategy may be more common than previously thought. Furthermore, 

when beaver do not build dams, they are less conspicuous and thus more easily overlooked

(Petro et al. 2015).

*************
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Section II - Beaver Restoration and 

Management

Photo Credit: Michael Pollock
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Chapter 4—Watershed Planning for Beaver 

Restoration Projects

Michael M. Pollock, Kent Woodruff, and Chris Jordan

Encouraging beaver to build dams and create ponds is an affordable and effective habitat 

restoration technique. In broad terms, there are three general beaver restoration approaches: 

 Passive actions such as trapping restrictions or changes in grazing regimes

 Active habitat manipulation to entice beaver to build dams and establish colonies

 Actively relocating beaver to areas with the intent that they will establish colonies 

Frequently there is considerable synergy among the three approaches. Reintroduction efforts, 

in particular, often are synchronized with trapping restrictions and habitat improvement 

efforts. 

We view beaver as a watershed-scale restoration “tool.” Beaver can be used to restore 

conditions at an individual site, but any beaver colony is part of a larger population, and the 

population dynamics of beaver are such that colonies form and disappear at different rates 

across the landscape. This means that any particular location that is suitable for beaver may 

not always be occupied. Furthermore, successful site-specific beaver restoration results in the 

production of beaver that disperse and contribute to the larger population, so even a sitespecific beaver restoration effort will have watershed-level implications. Nonetheless, all 

restoration actions ultimately take place at a site, and many techniques are available to 

encourage beaver to occupy or remain at a specific site for longer periods than would occur 

under natural conditions. 

We discuss specific restoration and management techniques for encouraging beaver to 

establish dam-building colonies but do not focus on establishing bank beaver colonies. Not all 

beaver build dams or wood lodges, instead, some so-called “bank” beaver establish 

reproducing colonies by building lodges in banks. Bank beaver have not been particularly 

well-studied, but observations suggest that they can exist in the same streams as dam-building 

beaver, that dam-building behavior can be triggered in bank beaver, and that dam-building 

beaver can stop building or maintaining dams and adopt a bank beaver lifestyle. In this 

manual, we focus on restoring dam-building beaver behavior because beaver dams and the 

water they impound create multiple ecosystem benefits, whereas the benefits of bank beaver 

are more limited (although evidence is growing that even the slow-water habitat created by 

the slides, burrows, and tunnels of bank beaver can be extensively used by juvenile salmon) 

(M. Pollock, K. Woodruff, personal observations).

Planning and Implementation Framework

To induce dam-building at a specific location, beaver are needed at the site. But where do the 

requisite beaver come from? There are several options: 
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(1) beaver can be reintroduced from an offsite location, 

(2) beaver from a nearby colony can be triggered to recolonize the site, or 

(3) dam-building behavior at the site can be triggered in an existing population of bank 

beaver. 

In each case, many of the steps in the restoration process are similar. Figure 11 provides a flow 

chart to follow in making decisions about beaver restoration actions. 

We use Figure 11 as a collaborative, watershed-scale framework for discussing specific actions 

to induce the establishment of dam-building beaver colonies. We approach beaver restoration 

from a watershed scale because that is the scale that is most likely to lead to successful colony 

establishment and a stable population. However, the approach described here can be adapted 

to a site-specific scale, as long as there is awareness of the larger watershed context within 

which the site-specific restoration actions occur. Below we provide an overview of previous 

efforts to establish beaver colonies, followed by a discussion of each of the steps in the 

restoration process outlined in Figure 11.

Goals, strategies, and objectives

Developing project goals and objectives, as well as a strategy for reaching the goals are key to 

any successful project. For the purposes of this document, goals, strategies, objectives, and 

tactics are defined as follows:

 A goal is a broad, primary desired outcome.

 A strategy is the approach you take to achieve a goal.

 An objective is a measurable step you take to achieve a goal, consistent with 

the strategy.

 A tactic is a tool you use in pursuing an objective associated with a strategy.

Identifying the project goals is an essential first step, after which strategies, objectives and 

tactics can be developed that will best achieve the goals. 

Goals

A beaver restoration project could have any of a number of goals: 

 Address nuisance beaver problems via non-lethal methods

 Restore beaver populations

 Increase water storage or raise water tables

 Restore wetland habitat

 Restore habitat for a particular species (e.g. salmon, Cascade frog, or willow flycatcher)

 Restore mountain (i.e., wet) meadow habitat

 Restore riparian habitat

 Increase floodplain connectivity

 Restore incised streams
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Figure 11: Flow chart for data acquisition and decision-making process in beaver restoration 

projects.

Strategies

Developing a strategy is the next step. A strategic assessment identifies both potential routes 

for moving forward to achieve the desired goals as well as the likely obstacles. Many of the 

goals above can be achieved through multiple approaches that don’t necessarily involve 

beaver or beaver dam analogues (BDAs), but for the purposes of this document, we assume 

that a broad strategic decision has already been made to use these beaver restoration tools. 

However, if at some point it becomes apparent that the chosen beaver restoration strategy is 
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not likely to be effective, it is important to remember that other restoration strategies exist and 

can be employed in conjunction with or separately from beaver restoration strategies. 

Strategic considerations are many and could include any of the following, among others:

 Where is there support for the project with landowners/land managers, the regulators 

and the general public?

 To what extent will educational components be needed for landowners/land 

managers, regulators, and the general public?

 What is the regulatory environment? Are any regulatory changes needed?

 How extensive is the willing landowner base? Can it be expanded if necessary?

 How can the effects of nuisance beaver be mitigated?

 What is the size of the project area?

 How much pre-project habitat assessment is needed?

 What is the timeframe for project completion?

 What is the project funding strategy? (Although of key importance, this topic is not 

discussed in this document.)

Objectives

Objectives can serve as benchmarks or targets that are helpful in determining whether the 

overall goal is being achieved. Examples of objectives might be to install a set number of 

BDAs, relocate a specific number of beaver, mitigate problems created by an identified

number of nuisance beaver, or establish a certain number of new beaver colonies. Related 

objectives might be to increase the amount of slow-water habitat by a proscribed amount, 

institute a specific regulatory change, or provide a certain number of educational interactions. 

It is helpful if objectives are quantifiable. Good monitoring programs quantitatively assess 

whether the objectives are being achieved.

Goals, strategies and objectives should all be dynamic and included as part of the adaptive 

management feedback loop. If monitoring suggests that project objectives are not being 

realized, then the project’s strategies or goals may need to be revisited.

Project Area

The project area includes the area where the restoration is intended to occur, and, if relocating 

beaver is part of the strategy, the population source area. The restoration area should include 

both the restoration and/or release sites, and, if the project is likely to increase beaver 

populations, a larger area that includes where beaver might be likely to emigrate. If the 

emigration area includes landowners who are opposed to having beaver on their property, a 
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strategic decision needs to be made as to whether to offer to mitigate for or relocate beaver 

that become established in areas where they are unwanted.

Time Frame

Good project development requires an estimate of the number of years or decades needed to 

achieve project goals. When working with beaver to restore streams, it is helpful to take the 

long view, and to put in the effort needed to develop lasting relationships with people, beaver, 

and streams. 

Beaver restoration projects tend to take longer than many other types of restoration projects 

because it is often necessary to change the way people think about managing both streams and 

beaver, and this takes time. In addition, because beaver are a living creature, they cannot be 

engineered to create habitat the way say, a piece of large wood might be engineered to 

provide a pool. It takes time for beaver to establish a colony in a new location and for the 

habitat benefits of the colony to be realized, as hydrologic, geomorphologic, and biological 

changes occur in response to beaver dams. Ideally, a beaver restoration project should have a 

minimum time frame of at least 5 years. It may be designed to extend for decades or longer, 

particularly if the goal is to initiate process-based changes to the physical condition of streams 

and riparian areas over large spatial scales.

Potential Collaborators and Resource Assessment

Because of the watershed scale at which beaver populations are maintained, and the multiple 

physical and biological processes that are affected by beaver dams, beaver restoration efforts 

usually require a collaborative effort by multiple organizations. Creating a cooperative 

relationship among organizations also helps diversify implementation of the tasks at hand. 

Some partners may have access to solutions that others don’t. For example state wildlife 

agencies may have the most expertise at handling beavers. Typically they are trained, 

equipped, and permitted to trap and move beavers, whereas other organizations might face 

logistical or regulatory hurdles. Other agencies or non-governmental organizations may have 

ready access to geographical information system (GIS) data.

Identifying which permits are needed for the project may guide you to potential collaborators. 

Developing positive, collaborative relationships with agencies from which you will need 

permits is always a good strategy. In addition to permit facilitation, people from other 

organizations may have access to labor, expertise, and funds. Perhaps most important of all,

they may have already established relationships with the managers or owners of the land 

where you would like to engage in restoration actions. 

Identifying available collaborators and incorporating them and the resources they bring into 

the restoration effort is an ongoing and dynamic process that may require you to modify the 

initial project goals. Clarifying roles and commitments is an important part of any 

collaborative process, and developing written cooperative agreements and funding 

instruments is essential for projects to function over the long-term.
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Assessing Habitat Quality for Beaver

There is a long and ongoing history in the development of methods for predicting where 

existing or potential beaver habitat exists (see Table 6). This fact in and of itself suggests that 

consensus is lacking as to what constitutes good beaver habitat and that there is no one tool 

appropriate for assessing a watershed in terms of beaver habitat suitability. 

Table 6: Physical and Biological Parameters of Stream Reaches Used to 

Estimate Suitability as Beaver Habitat. Studies are arranged chronologically, left 

to right, from oldest to youngest. Locations are all U.S. states, except as follows: 

RM = Rocky Mountains, US = United States, ON =Ontario, Canada.

Location R

M

U

S

M

A

C

A

S

D

O

R

K

S

O

N

O

N

O

R

W

A

I

L

W

V

U

T

W

A

Physical Variables

Stream slope X X X X X X X X X X

Stream depth or 

width X X X X X

Stream power (Q*S) X X X X

Valley bottom width X X X X

Stream length X

Stream substrate X X X

Bank slope X

Water quality X

Water fluctuations X X

Basin size X X X

Biological Variables

Habitat area X

Vegetation X X X X X X X X X X X

Land use /

development X X X X

Reference 1 2 3 4 5 6 7 8 9

1

0

1

1

1

2

1

3

1

4

1

5

References: 1= Retzer et al. = 1956; 2= Allen 1983; 3 = Howard & Larson 1985; 4 = 

Beier & Barrett 1987; 5 = Dieter and McCabe 1989; 6 = McComb et al. 1990; 7 = 

Robel et al. 1993; 8 = Barnes and Mallik 1997; 9 = Slough and Sadleir 1997; 10 = 

Suzuki and McComb 1998; 11 = Pollock et al. 2004; 12 = Cox and Nelson 2008; 13 

= Anderson and Bonner 2014; 14 = MacFarlane and Wheaton 2014; 15 = 

Dittenmeier et al.unpublished data.
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Additionally, experimental relocation efforts that have used habitat suitability models to find 

good release sites have universally observed a high rate of emigration by the released beaver

(McKinstry and Anderson 2002, Babik and Meyer 2013, Methow-Beaver-Project 2014). This 

suggests that existing models may need refinement. Nonetheless, there are some basic 

physical constraints on where beaver can establish dam-building colonies within a stream 

network, and potential beaver habitat can often be described by three physical variables; 

stream gradient, stream width, and valley bottom width, while a fourth, biological variable—

vegetative condition—is also often used to predict where suitable beaver habitat exists (Table 

6).

Years of data collection by numerous observers suggests that most dam-building colonies are 

established on small to medium-sized, low-gradient streams that are unconstrained within a 

valley bottom (Table 6). Large rivers, high-gradient streams, and confined channels tend not to 

support beaver colonies, but there are always exceptions, particularly when beaver are 

abundant and all the high-quality habitat is already occupied. What is often surprising is how 

little water beaver need to build dams. Small ephemeral streams, springs, and seeps can be

dammed by beaver to create perennial ponds. Some beaver seem to have an uncanny ability to 

identify hydrologic conditions that are suitable for pond formation, including locations that 

habitat suitability indices may not identify because these areas have drainage areas so small 

that they are not even recognized as streams (let alone perennial streams) on GIS data layers. 

In addition, stream layers are often missing side channels on large rivers, yet beaver 

frequently dam such channels. Using GIS analysis tools to identify these areas can be 

challenging, and thus they are often overlooked or ignored as potential beaver habitat. 

Ideally a beaver habitat assessment is performed at the watershed and larger scale and 

includes some basic coarse-scale categories of beaver habitat suitability or capacity for dam 

building. At the broadest scale, stream networks can be divided into stream reaches that have 

no, low, medium, or high intrinsic potential as beaver habitat or dam capacity. Streams with 

high intrinsic potential can further be divided into areas with and without active colonies. 

Reaches with medium to high intrinsic potential or capacity, but without active colonies can 

be further divided into reaches with beaver activity but no dam-building colonies, reaches 

with abandoned colonies, reaches without beaver that have existing high-quality habitat, and 

areas that could have existing high-quality habitat but are in need of restoration. Thus a 

stream network can be divided into six basic categories in terms of beaver habitat suitability 

(see Figure 11):

 Low/no/unknown intrinsic potential or dam capacity

 High/medium intrinsic potential or dam capacity

o Active dam-building colonies

o Abandoned dam-building colonies

o Beaver activity but no dam-building colonies

o No beaver, but habitat suitable for colonization by dam-building beaver

o Potentially good beaver habitat but needs restoration 

Each category requires different restoration tools to achieve the desired outcomes.
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Recently, MacFarlane and colleagues (MacFarlane et al., 2014, 2015) developed a GIS/Fuzzy 

Logic tool to evaluate dam building capacity across watersheds. The Beaver Restoration 

Assessment Tool (BRAT) was developed to address two perceived needs in supporting beaver 

based restoration: firstly, the need to quantify riverscapes in terms of habitat to support dam 

building activity (capacity model); and secondly, to identify the spatial extent and degree of 

potential interaction between dam building and anthropogenic land use activities (conflict 

model). Thus, BRAT is a decision support and planning tool that resource managers, 

restoration practitioners, wildlife biologists and researchers can use to assess the potential for 

beaver as a stream conservation and restoration agent over large regions. 

The BRAT capacity model uses stream flow characteristics, valley topography and vegetation 

information to estimate the dam building capacity of riverscapes (Table 7). The capacity 

model outputs dams per km and has been calibrated to a range of dam densities, 0 - 40/km, 

encompassing the range found in nature and reported in the literature (c.f., Gurnell, 1998).The 

capacity model is a set of GIS tools that can be run based on a generic rule-set and it can also 

be adjusted based on local conditions if regional or higher resolution data are available. 

A recent application of the BRAT capacity model applied across the entire state of Utah (Fig 

12) generated statewide estimates of beaver dam densities at current and historic capacity 

based on the following five lines of evidence (Wheaton & MacFarlane, 2014):

 Evidence of a perennial water source.

 Evidence of stream bank vegetation to support dam-building activity and 

riparian/upland fringe vegetation to support expansion of dam complexes.

 Evidence that a beaver dam could physically be built across the channel during low 

flows.

 Evidence that a beaver dam is likely to withstand typical floods

 Evidence of low enough stream gradient to allow for dam building by beaver.
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Figure 12: Modeled beaver capacity based on current conditions in Utah (MacFarlane et al. 

2014).
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The five lines of evidence used by the BRAT capacity model can be directly measured with a 

high degree of accuracy for each watershed or river system being evaluated; however, 

assuming that basic geomorphological and ecological principles have been captured in the 

model rule set allows estimates also to be generated from widely available, free, national 

datasets and regionally derived empirical relationships (Table 7).

Table 7: Input data used to represent each of the five lines of evidence of the BRAT capacity 

model (from MacFarlane et al., 2014)

Input data Line of evidence Source

Streams, waterbodies Perenial water source USGS National Hydrography Dataset 

http://nhd.usgs.gov

Landfire 2011 (EVT and BPS) Riparian and upland 

vegetation

Landfire land cover data 

http://www.landfire.gov

USGS base flow regression 

equations

Dam could be built Wilkowske et al., 2008 

http://pubs.usgs.gov/sir/2008/5230

USGS 2 year peak flow 

regression equations

Dam could withstand 

typical floods

Kenney et al., 2007 

http://pubs.usgs.gov/sir/2007/5158/

10 m Digital Elevation 

Model (DEM)

Stream gradient USDA NRCS Geospatial Data 

Gateway 

http://datagateway.nrcs.usda.gov/

GIS tools also can be used to further filter the landscape by identifying the property 

boundaries of cooperating and non-cooperating landowners, jurisdictional boundaries where 

beaver management regulations may vary, habitat distribution maps for other species that 

may be the target of the restoration efforts (e.g. salmon), habitat types that may be the focus of 

restoration efforts (e.g., mountain meadows), and locations where there may be beaverinfrastructure conflicts (e.g., road and stream crossings).

Once a GIS-based map has been created, the beaver habitat categories need to be ground 

truthed. Ground truthing is the only means of identifying the sixth category of beaver habitat 

suitability: locations where beaver are present but not part of an active dam-building colony. 

Figure 15 is an example of a beaver habitat scoring sheet, developed by the Methow Beaver 

Project, that has been used by several projects to evaluate the quality of beaver habitat on the

ground; this aids in identifying areas where beaver can be relocated. Such a scoring system is 

useful in assessing and improving the accuracy of the habitat classification and capacity 
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estimation derived from remote sensing but also in helping to further refine the relative 

quality of good beaver habitat and identify the sites where beaver reintroductions are most 

likely to be successful. Key on-the-ground variables the scoring system uses include riparian 

condition, beaver activity, food availability, substrate and geomorphic parameters such as 

stream gradient and width, floodplain width, and the general size of the available habitat. 

Filters (External Constraints)

Landowner Assessment

A key external factor that affects the success of beaver projects is the spatial distribution of 

land where beaver are wanted (or tolerated). Property boundary maps are available for most 

jurisdictions. Managers of public land are generally (but not always) supportive of beaver 

restoration efforts, but beaver do prefer low-gradient areas in valley bottoms, and such areas 

often are privately owned. However, a growing number of private landowners are 

recognizing the benefits of beaver dams, and support for allowing beaver on private lands is 

considerable (Morzillo & Needham 2015). In many places, identifying and developing a 

network of private landowners who support beaver restoration efforts is an essential early 

step.

Potential infrastructure conflicts should be identified and mapped. Examples of instream 

infrastructure that has the potential to create conflicts with beaver restoration efforts include 

culverts, stream gages, outfalls irrigation/diversions ditches, weirs, and fish screens. On 

floodplains near stream channels, flooding from beaver dams can cause conflicts related to 

human infrastructure such as buildings, roads, and commercial crops. In addition, beaver use

Some commercial crops, such as Populus plantations, alfalfa fields, and even watermelon, as a 

food source to varying degrees if the crop is growing near a stream (see Appendix A).

To directly estimate the potential for beaver-human conflicts, MacFarlane and colleagues 

developed a Human-Beaver Potential Conflict Model (MacFarlane et al., 2014). The conflict 

model uses generally available spatial data to characterizing potential points of conflict, 

including transportation (canals, roads, culverts, railroads, stream crossings by roads) and

water related land use and land ownership to estimate the probability of potential conflict. 

The conflict model is based on proximity of dam bearing reaches (from the BRAT capacity 

model) to human built or used landscape features. Applying logical transformations (see 

Figure 13), to these distances generates a probability of human-beaver conflict 

Figure 13 is a graphical representation of the conflict model’s conditional logic. Since the 

model is conditional, each set of probabilities of conflict (e.g. roads, culverts, railroads, etc.) is 

filtered by the most restrictive, highest probability. The rule set for ranking amongst 

individual conflict sources is user determined. For example, in regions or areas where 

managers and stakeholders are more willing to use ‘living with beaver strategies’, the absolute 

and relative mangnitude of specific conflict probabilities could be lowered; whereas, in areas 

where there is less tolerance for potential nuisance beavers, they could be increased. As such, 

this particular method for estimating, quantifying, and mapping in a spatially rigorous 

manner potential human-beaver conflicts can be applied across a wide range of social, 

biological and geographic settings (Fig 14). 
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Figure 13 – Flowchart diagramming the human-beaver conflict potential probability model. 

The initial probability values are very restrictive, resulting in many areas with high probability 

of conflict values. These probabilities can be adjusted to reflect stakeholder desires.
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Figure 14 – Combining the estimates of dam building capacity and human conflict allows the 

generation of statewide Beaver Management, Conservation and Restoration Zones. (from 

MacFarlane et al., 2014).
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Methow Beaver Project Release Site Score Card (2015 update) Date_________________

Site ID________________________________ Observer______________________________

GPS Coordinates_UTM (NAD 83)___________________________ Subwatershed__________________________

Lat x Long______________________________ Location Description ___________________________________

_______ Gradient of the assessed stream habitat unit 10. ≤3% 0. 4-6% -10. 7-9% -30. ≥9%

Min (fall)

 Stream Flow 

 _______

 

 Max

(spring)

NOTE – Stream flow above or below these parameters limits beaver dam viability

_______ Habitat Unit Size (linear stream measure) 5. Extensive stretch of the stream 1. Small isolated pocket

 Woody Food (select the highest number possible in each line – then multiply lines)

a. 3. Aspen, willow 2. Alder 1. Other hardwoods

 b. 3. Within 10 meters 2. Within 30 meters 1. Within 100 meters

 c. 2. Large amount (hundreds of stems) 1. Some (dozens of stems) 

_______ Woody food score = multiply a x b x c

_______ Herbaceous Food 10. Grasses and forbs (aquatic and terr.) abundant 5. No Grass/Forbs Present

_______ Floodplain Width 5. Wide stream bottom 0. Narrow ‘V’ Channel

 Dominant Stream Substrate

5. Silt/Clay/Mud 2. Sand 1. Gravel 0. Cobble -1. Boulders -3. Bedrock

 Historical Beaver use

15. Old structures present 0. No indication of previous occupancy

 Lodge and dam building materials

5. abundant 1-6” diameter woody vegetation available -20. no building material present 

 Browsing / Grazing impacts

5. No Impact or obvious presence of browsers / grazers -10. Heavy browsing / grazing

_______ Ease of access 2. Easy travel to deliver beavers and monitor. -5 Long hike 

____________ Existing aquatic escape cover 10. Multiple deep pools (>1 meter deep) present. -10. No pools 

 Total Score (100 points maximum)

Release site viability requires securing adjacent landowner support and careful mitigation of human 

infrastructure conflicts in the vicinity.

Narrative description of site and notes/ Photo ID #s / sketch on back

Figure 15: Methow Beaver Project Potential Release Site Score Card.

garden hose fire hose 10”culvert 30” culvert

Fire hose 1

10” culvert 3 4

30”culvert 4 5 10

un-wadeable 1 3 2 1
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Project Goals Assessment

Project goals usually constrain the potential extent of the project. For example, if a beaver 

restoration project focuses on a target species, habitat type, or habitat condition, the potential 

project area will be limited to places where those species or habitat types could occur. 

Examples of taxa for which beaver can improve habitat include salmon and steelhead, 

waterfowl, amphibians, and certain songbirds, such as the willow flycatcher. Examples of 

habitat types or conditions that beaver can help restore include mountain meadows, incised 

streams, off-channel habitat, wetlands, and riparian vegetation.

Jurisdictional Assessment

Federal, tribal, and state governments all have a certain amount of jurisdictional authority 

over the management of beaver. Which agency has regulatory authority over which lands is a 

matter of debate. In general, state legislatures and state fish and wildlife departments set the 

rules for beaver management across the state, but Indian nations and federal agencies that 

own or manage land within a particular state’s boundaries sometimes develop their own 

beaver management or other natural resource management guidelines, as when, for example, 

the National Parks Service sets fishing regulations within the boundaries of its parks. 

Further complicating matters is that some state agencies have developed specific beaver 

management guidelines that are tied to restoration funding and that may not necessarily be 

consistent with state laws or fish and wildlife department rules. The state of Oregon is 

particularly complex, with state laws, Oregon Department of Fish and Wildlife (ODFW) 

regulations, ODFW guidelines, and even an Oregon Department of Justice legal opinion, all 

guiding the management of beaver within the state. Finally, the National Oceanic and 

Atmospheric Administration and the U.S. Fish and Wildlife Service, the two Federal agencies 

that oversee the recovery of species listed under the U.S. Endangered Species Act (ESA), both 

recognize the importance of beaver-created habitat to the recovery of some endangered 

species, such as coho salmon. Thus using beaver or beaver dam analogues within the range of 

endangered species such as salmon usually requires consultation with these agencies. The 

coordination of jurisdictional authority of beaver, beaver dams, and beaver dam analogues 

among and between state, Federal, and tribal authorities is an ongoing, fluid, and dynamic 

effort.

Permit Assessment

Key to any successful restoration effort is acquisition of the necessary permits. Identifying and 

obtaining the necessary local, state, Federal and tribal permissions can often be the most timeconsuming and confusing aspect of a restoration project. It can take agencies months to years 

to process permit applications, so it is best to begin identifying the necessary permits early on 

in the project. This is especially true for beaver restoration permits because many agencies 

have not yet figured out how to process various restoration projects that involve beaver, 

beaver dams, and beaver dam analogues. 
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The following are some common regulatory issues concerning beaver:

 Movement of reintroduced beaver to offsite locations where they are unwanted

 Fish passage over beaver dams or beaver dam analogues

 Turbidity

 Increased stream temperatures

 Flood damage to private property

 Flood damage to public infrastructure

 Downstream effects of dam failures

 Bank erosion

 Loss of riparian vegetation

 Loss of agricultural crops

 Loss of ornamental vegetation

 Habitat changes upon colony abandonment

 Degradation of habitat important to state or Federal ESA-listed species

 Assignment of liability associated with any of these perceived negative effects

Although many of these concerns are not well-founded for most situations, some may have to 

be addressed in the permitting process. Furthermore, individuals within regulatory agencies 

are not necessarily well-versed in the ecosystem benefits of beaver dams and may be more 

concerned about avoiding negative effects than creating positive outcomes. For a beaver 

restoration project to be successful, the concerns of the individuals within regulatory agencies 

who are responsible for issuing permits must be understood and addressed. It is essential to 

be able to convey the benefits of beaver restoration so that regulators can weigh potential risks 

against potential rewards and reach a determination that the project will provide an overall 

beneficial outcome.

State and Federal permits fall into the following broad categories, among others:

State:

 State Environmental Policy/Quality Act review

 Instream work permits

 Trapping and release permits

 Wild animal husbandry permits

 Archaeological/historical preservation permits

 Water Board permits

Federal:

 National Environmental Policy Act (NEPA) review (for Federal lands)

 Consultation with USFWS and National Oceanic and Atmospheric Administration 

(NOAA) Fisheries if ESA-listed species are in the area

 U.S. Army Corps of Engineers permits for instream work

Depending on the location of the restoration project, many of these permits may already be 

addressed under programmatic permits that cover specific types of actions over a specific 

geographic area, or a specific agency may have a programmatic permit from another agency. 
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For example, the Aquatic Resources Biological Opinion (NMFS 2013) provides ESA coverage 

for the construction of beaver dam analogues on U.S. Forest Service (USFS) and Bureau of 

Land Management (BLM) lands in Oregon and Washington, while the Malheur National 

Forest in eastern Oregon has adopted a memorandum of understanding for managing beaver 

on its lands (Malheur-National-Forest 2007) and the U.S. Army Corps of Engineers has created a 

nationwide permit (NWP 27) which allows for a wide range of stream restoration actions 

consistent with Section 404(e) of the Clean Water Act. Developing collaborative relationships 

with agencies or organizations who already hold permits needed for beaver restoration and 

may be familiar with the current regulatory environment can aid in successfully navigating 

the permitting process.

Community Assessment

Most watersheds exist within a community of people, and it is important to gauge the level of 

local community support for beaver restoration activities before proceeding with a project.

Community opposition can stop a project, while community support can ensure its success. 

Spending time building support for beaver restoration in your local community can help 

facilitate long-term success. In particular, many regulators are reluctant to approve beaver 

relocation projects because of the perception that most landowners do not want beaver on 

their property, although this perception seems to be a bit dated (Needham and Morzillo 

2011).Although beaver can be established at specific locations without community support, if 

the goal is to create or expand a sustainable population of beaver within a watershed, a certain 

amount of educational effort will be needed so that people better understand that the benefits 

of beaver far outweigh the problems they may create, and that most of the problems can be 

addressed with proper management. Community support can also be helpful when regulators 

are considering whether to issue permits.

Evaluate options

As outlined in Figure 11, there are five tools that can be used to encourage or simulate dambuilding behavior in beaver: 

 Reintroducing beaver

 Building dams

 Providing food

 Providing lodging

 Planting riparian vegetation

There are also tools for addressing problems caused by beaver:

 Education

 Mitigation 

o Caging vegetation

o Protecting culverts

o Water level controls

 Relocation

 Termination (i.e., lethal removal)
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Additional indirect tools that are useful in long-term beaver restoration efforts are:

 Working on regulatory changes

 Working on land management changes, particularly for public lands

Each of these tools has a role to play in beaver restoration projects, with the appropriate set of 

tools being determined by the project’s goals and the risks and rewards associated with each 

project option. The next sections discuss these restoration tools, with an emphasis on the 

mostly commonly used of these tools: reintroduction efforts and construction of beaver dam 

analogues. 

We also discuss the use of a Beaver Dam Viability Matrix in Chapter 10 (Figure 40), which is 

intended to assist project managers in quickly assessing the likelihood that a beaver dam will 

persist over at least two seasons—the time necessary for a mating pair of beaver to 

successfully rear their offspring. Depending on where a project site plots on the matrix, 

appropriate restoration techniques and tools can be selected or an alternative site pursued. 

*************
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Chapter 5—Relocating Beaver 

Kent Woodruff and Michael M. Pollock

Overview of Relocation Efforts 

In North America, there is a relatively long history of reintroducing beaver to areas from 

which they have been extirpated, primarily in the hopes that they would build dams and 

create ponds. In the United States, beaver reintroductions began in the early twentieth century

across the continent from New York to California (Radford 1907, Tappe 1942). Most 

reintroduction programs were successful to the point that trapping bans were lifted so that 

populations could be controlled.

Early reintroduction programs were not concerned with maintaining genetically distinct 

populations, and many reintroductions used beaver from distant locations. As a result, there 

has been an unknown amount of genetic mixing. For example, reintroduction efforts in 

California used beaver from Idaho, Oregon, and California (Lynn 1949). Although numerous 

subspecies of the North American beaver, Castor canadensis, have been proposed in the past

(Baker and Hill 2003), the Integrated Taxonomic Information System (ITIS.gov) currently 

recognizes C. canadensis as a single species and does not consider any of the many proposed 

subspecies “valid” (Appendix B). The International Union for the Conservation of Nature Red 

List (IUCNredlist.org) rates C. canadensis as “least concern,” which is the lowest level of 

concern for a species in terms of its likelihood of becoming extinct. The IUCN considers the 

population of North American beaver stable and widespread throughout its range. These 

findings suggest that taxonomists and conservationists do not recognize distinct genetic 

populations of C. canadensis, and that unwanted genetic mixing between potentially distinct 

populations is not a high-priority concern. Much more effort should be focused on 

understanding beaver population genetics and identifying genetically distinct population 

segments, as well as linking specific life-history or behavioral characteristics with genetically 

distinct populations.

Beaver restoration efforts in the early to mid-twentieth century in the western United States 

generally did not focus on quantitative measures of success. Some efforts appear to have been 

successful, while for others, the success rate is unknown. For example, in 1948, Heter (1950) 

released 76 beaver (by parachute) on Forest Service lands in Idaho. One year later surveys 

indicated that the airborne transplants were successful, but the number of release sites was not 

stated. Lynn (1949) documented California transplant efforts in the 1930s and 1940s, when 

1,208 beaver were released at 274 sites. The success rate was not stated. Hibbard (1958) 

reported the transplant of 466 beaver in North Dakota. Again, no success rate was 

documented. In Washington, Sheffer (1938) successfully transplanted beaver for the purpose 

of building dams to control sediment in Mission Creek. The project was largely successful, 

with 22 dams being built and more than 3,924 cubic yards of sediment being stored behind 

beaver impoundments. Also in Washington, in Okanogan County, in the 1930s a total of 76 
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beavers were released at 40 sites. Eighteen of these resulted in successful establishment 

(Okanogan Wenatchee National Forest unpublished records).

Today, beaver relocations are often proposed as a non-lethal means of dealing with so-called 

“nuisance” beaver that are in conflict with humans, usually because they are either flooding 

property that landowners do not want flooded, damming culverts, affecting irrigation ditches, 

or cutting down trees (e.g., see Revised Code of Washington [RCW] 77.36.160). Yet other 

landowners recognize and value beaver dams’ numerous hydrological and ecological effects 

and want to have the animals on their property (e.g., see RCW 77.32.585).

Recent studies suggest that re-establishing beaver colonies by relocating beaver to areas where 

they are not currently found can be challenging, and that mortality rates for the relocated 

beaver can be high (McKinstry and Anderson 2002). At the same time, a number of beaver 

habitat suitability models have been developed that relate beaver dam or colony abundance to 

physical and biological habitat characteristics and use of such models should help reduce 

mortality (see Table 6).

These models vary in their utility for identifying sites where relocated beaver are likely to 

successfully become established. Why relocated beaver do or do not become successfully 

established at or near release sites is not entirely clear, although recent studies provide some 

insights. 

In Wyoming, McKinstry and Anderson (2002) relocated 234 beaver to 14 sites over a 6-year 

period. They radio-tagged 114 beaver and found that mortality rate was 30 percent and the 

emigration rate (i.e., moving more than 6.2 miles from the release site) was 51 percent, 

inclusive of transmitter failures. They estimated a survival rate of 49 percent after six months 

and 43 percent after a year. Animals less than 2 years old had a mortality or emigration rate of 

100 percent after 6 months. The high overall mortality was attributed to abundant predators 

(coyote, black bear, grizzly bear, mountain lions, and humans) and limited cover. The release 

sites contained shallow water, with no ponds and little protection. No food, lodging, or dams 

were provided. However, 13 of the sites had evidence of old beaver activity, indicating good 

habitat potential, and all sites had abundant riparian vegetation. Because the release sites were 

a long distance from the capture sites the beaver were temporarily retained and transported as 

groups on a weekly basis; however, it was not clear whether individuals from a trapped 

colony were released at the same site. Releases occurred primarily in the fall because that is 

typically when beaver construct new dams and lodges. Some beaver were successfully 

released in the spring at sites where flow tended to be ephemeral, but the relative survival 

rates for spring versus fall releases were not compared. Despite the high mortality and 

emigration rates, beaver were successfully established at 13 of 14 sites (beaver were removed 

from one site because of conflicts with agriculture). Twenty-three beavers (i.e., 19 percent) 

lived more than 6 months and eventually built dams and lodges near the area where they 

were released. Another 10 were found in dams and lodges within 1.86 miles of the release 

sites. On average, 17 beaver were transplanted to each release site before the successful 

establishment of dams and lodges.

In the Methow Valley in north-central Washington, Woodruff (2015) has an ongoing beaver 

restoration project that has relocated 240 beaver to 51 sites from 2008 to 2014, for an average of 
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4.7 beavers per site. As of November 2014, there was activity on 17 sites (34 percent), and 31

(61 percent) had established dam-building colonies. The 31 successful sites average 0.46 acres 

of surface water. Fifteen well-established sites average 0.89 acre of surface water, with an 

average of five ponds per site. In 2014, 38 beaver were released to 13 sites (an average of 2.9 

per site), and eight of those sites (62 percent) saw successful establishment the first year.

Unlike many relocation projects, the Methow Beaver Project is providing considerable 

assistance at the release sites; it is likely that this is contributing to project success. Prior to 

releasing beaver, the project team constructs artificial lodges and provides an initial source of 

food (aspen—Populus tremuloides). Furthermore, many release sites contain deep pool cover

(i.e., more than 1 meter deep). 

Quantifying the long-term success of the Methow Beaver Project has been somewhat 

challenging because reintroduced beaver have occupied sites one year, only to abandon them 

and move elsewhere the next. In some instances, based on passive tagging information, beaver 

that were introduced to a site immediately went elsewhere. In three cases, when another 

group of beaver were introduced to the same site they elected to stay and build dams. The 

project illustrates the difficulty of predicting the behavior of any individual beaver or group of 

beaver, in particular when and where they will establish a colony. In general the project 

results suggest that carefully planned beaver reintroductions can increase the density of dambuilding colonies on the landscape, but the precise location where colonies will be established 

cannot always be predicted.

In the Yakima River basin in Washington, another collaborative beaver restoration effort has 

met with considerable success by adopting and modifying the Methow Valley methodology

(Babik and Meyer 2013). The Yakima Beaver Project has been managing beaver complaints in 

the Yakima Valley through a combination of education, mitigation, and relocation. From 2011

to 2014 they received 134 nuisance beaver complaints, primarily in the agricultural lowlands 

and near urban areas, and have relocated 130 beaver to Forest Service lands in the highelevation headwaters of the Yakima River. Of these relocated beaver, 81 (62 percent) have 

moved to unknown locations or died. Thirteen were monitored moving to a different area, 

with the greatest movement being more than 40 miles in 47 days. Of the remaining 49 beavers, 

two died and 47 (36 percent) were successfully established in 17 colonies within a year of

being released. The number of beaver relocated per known successful colony was 7.6, but 

subsequent field surveys of streams near the release sites have found additional recently 

established colonies, suggesting that some of the beaver that dispersed from the release sites 

successfully established colonies elsewhere. The Yakima Beaver Project enticed beaver to stay 

at the release sites by providing lodges and food and releasing them in areas with deep pools. 

The project team used the same scoring system as the Methow Beaver Project (see Figure 15) to 

identify good beaver habitat, but even with these incentives, many beaver dispersed to other 

areas. In some cases the dispersing beaver established colonies elsewhere, indicating again 

that it is difficult to predict where translocated beaver will establish a colony but also that the 

success of a project can extend well beyond the initial treatment areas.

Petro (2013) studied the survival of 38 radio-tagged beaver released into nine sites in coastal 

Oregon. After 16 weeks, the survival rate was 47 percent, with predation by mountain lions 

the greatest source of mortality and with most of the mortality occurring within 1 week of
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release. Only one released pair engaged in dam building. They built six small dams in two 

locations, but the dams were ephemeral because of high winter flows. The suitability of the 

release sites was determined by using a beaver habitat suitability model for western Oregon 

(Suzuki and McComb 1998). The beaver received no assistance at the release sites such as a 

dam, den, or food. In addition, instead of being temporarily retained at a holding facility, they 

were released individually and immediately after capture, such that individuals from intact 

colonies were released to new sites over a period of about one to four days. 

Jackson and others (unpublished report) used nine physical and biological characteristics of 

sites with naturally occurring beaver dams to identify unoccupied sites with similar 

characteristics that they thought would be good relocation sites. From May to August of 2009, 

they captured, radio-tagged, and released 37 animals at 13 sites in Oregon’s Umpqua River 

basin. When the last transmitter quit working after more than 500 days, about 26 percent of 

the beaver had survived. Some beaver moved very little from the release site, some beaver 

moved around a bit and then returned to the release site, and some travelled a considerable

distance—up to 8 miles. The animals were released without being provided a dam, den, or 

food and were released during summer low-flow conditions.

In summary, multiple projects have successfully relocated beaver across a wide range of 

habitat. At the same time, most projects have documented many instances where beaver have 

failed to establish at a target location. The reasons for establishment failure are varied and 

often the reasons are not clear. Below we describe a relocation methodology that incorporates 

many of the lessons learned from the efforts cited above as well as incorporating lessons 

learned from other efforts that we did not describe. The methodology we present is the most 

comprehensive description of how to relocate beaver of which we are aware.

Relocation Methodology

Most recent relocation efforts have benefitted from the experience of prior activities. For 

example, the Methow Beaver Project in Washington relied on knowledge accrued by Mark 

McKinstry and others in Wyoming (e.g., McKinstry and Anderson 2002), the publication of 

results and techniques by John Vore in Montana (Vore 1993), guidelines developed for stream 

habitat restoration in the state of Washington (Washington Department of Fish and Wildlife

2004), and advice from Lew Pence in Idaho, who has years of beaver relocation experience 

(Woodruff 2015).

Current relocation projects in the western United States often include the following key steps: 

1. Identify suitable habitat (often using remote sensing).

2. Assess current beaver population status and distribution.

3. Evaluate individual release locations.

4. Pursue acquisition of beavers.

5. Collect information about beavers captured (or re-captured).

6. Care for beavers temporarily and ensure that beavers are grouped as families or 

compatible units with both males and females.

7. Prioritize and prepare release locations.

8. Deliver beavers to selected sites.

9. Conduct follow-up monitoring and provide support. 
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Identifying and Prioritizing Suitable Habitat for Releasing Beaver

The Methow Beaver Project developed and employed a GIS model for evaluating the 1,800-

square-mile target watershed that emphasized stream gradient and stream discharge as the 

key features for habitat suitability. This exercise identified approximately 160 highly likely 

reaches for beaver establishment. Additionally, known beaver occupancy from multiple 

stream survey efforts was mapped and compared with predicted suitable habitat. This 

allowed model inputs to be validated and adjusted.

A habitat assessment scorecard was created that was based on all available literature, 

consultation with people experienced in beaver management, and the local knowledge of 

Methow beaver crews (Figure 15). The scorecard allows individual sites to be ranked based on 

multiple factors, including many that are listed as risk factors in the Beaver Dam Viability 

Matrix (see Chapter 10). The scorecard should be modified for individual circumstances, as it 

has been over the years for the Methow Project. Factors evaluated include the availability of 

woody food and building material, stream gradient and flow, availability of existing aquatic 

escape cover, presence of herbaceous food, stream bottom character, potential for conflict with 

existing human activities, and past beaver presence. 

Sources of Live Beaver

Often when beaver restoration is pursued, the beavers themselves come from areas where 

landowners or land managers have concerns about human/beaver conflicts. Common 

concerns include orchard damage, culvert blockage, damage from flooding, trees fallen along 

roadways, fallen trees affecting buildings or vehicles, impacts to irrigation canals, beavers 

feeding in agricultural fields (e.g., alfalfa), and loss of ornamental or landscaping trees. Where 

it is not practical to mitigate beaver damage onsite (see section 9), removal can be initiated 

through live trapping, ideally using licensed trappers or others who are familiar with trapping 

and handling beaver.

Landowner Contact

Positive landowner relations are essential to the success of beaver relocation. Respecting 

landowner wishes is critical. Communication with landowners should include an assessment

of the potential conflict situations and messages about the value of beaver in enhancing

watersheds. This communication serves as an important foundation for gaining community 

acceptance of beaver restoration as a practice. It is helpful to clarify that beavers are not 

villains that always need to be removed, but that they have much to offer, especially as 

watershed function is more heavily emphasized throughout much of the western United 

States and elsewhere.

Live Trapping—Techniques and Equipment

Each state has specific guidelines, rules, and regulations for managing, capturing, handling, 

and relocating beavers that must be followed. Coordination with local biologists and 

enforcement agents is important. 
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Although capturing beaver is not difficult and can be learned through trial and error, relevant 

knowledge and experience can significantly improve the likelihood of success. Gaining tips, 

ideas, and tricks from experienced trappers is helpful and will substantially lower the slope of 

the learning curve. Because each beaver represents a substantial contribution to habitat 

improvement, enhanced stream function, and water storage, it is prudent, ethical, and 

respectful to limit injuries and impacts associated with trapping and transport. 

Hancock-style “suitcase” beaver traps (Figure 16) are a common method of capture, but other 

box and suitcase trap configurations have been employed successfully . Snares with “deer 

stops” are also used for live capture but require special authorization and training. 

Baiting traps placed on the edge of water bodies with scent lures and food, or placing passive 

traps on trails and near centers of heavy use, is common practice. Beavers like to investigate 

uncommon smells, especially those of unfamiliar beavers. Castoreum-based lures are available 

commercially or can be easily made using castor glands and oil glands from dead beavers. 

Breaching dams is another way to draw beavers to traps, as beavers are drawn to the sound of 

running water.

Traps should be set and then checked frequently. Beaver activity usually commences late in 

the day and goes through most of the night. Near-freezing temperatures and holding beavers 

in traps for an extended time can add stress, which can possibly affect the success of reintroduction. If temperatures are high and beavers are away from water, that too could be 

stressful. Conversely, if placed to close or far into the water beaver can drown in traps. Finally

beavers can be exposed to predators while in traps. Frequent trap checks are important.

Beaver Holding Facilities—Assessment and Care

Temporarily housing beaver has the potential to substantially improve successful

reintroduction rates. Some recent beaver relocation projects have employed very simple to 

very elaborate holding facilities (Babik and Meyer 2013, Methow-Beaver-Project 2013), while 

others have not held beavers at all following capture (Hoffman and Recht 2013, Petro et al. 2015).

However, allowing time for an entire group to be united before release (this can take several 

nights of trapping) seems to be an important part of successful reintroductions. 

In some cases success has been accomplished with immediate release. However, given the 

easy mobility of beavers in watersheds and the social, gregarious nature of this animal, it is 

unlikely that individual beavers would wait for others to arrive over succeeding days in an

unfamiliar location—and that they could avoid detection and predation long enough to

become established at the new location. It is also possible that the social factors of site selection 

are a cooperative decision for a group of beavers and that the decision is made based on the 

perceived capacity of the connected group. This is an area where more studies are needed.

Techniques and Equipment

Once beavers have been successfully captured, data should be collected on their age, weight, 

sex, and condition, and whether they have been encountered before. On long-term projects, it 

is helpful to mark captured beavers in some way so that individuals can be identified in the 

future. Marking with techniques that allow for ongoing movement monitoring is challenging. 
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Standard VHF or satellite telemetry has yielded limited results. PIT tag marking with readers 

in streams has also provided some movement data. 

Holding beavers in a temporary facility appears to contribute to the likelihood that the groups 

released will become established and create the desired watershed improvements, as long as 

the holding facility allows beavers to: 

 Be away from “the scene of the crime” for a while and disassociate with their original 

territory and the behavior that contributed to beaver/human conflicts

 Have time away from predation risk

 Become accustomed to other captured beavers and possibly form new bonds of affection 

within self-selected pairs and groups

 Have abundant food resources to improve body condition before release

 Be monitored for health and condition

Group size is determined largely by the trapping situation. A minimum of a male-female pair 

is needed. 

Intake Processing Procedures (Methow Beaver Project)

The techniques described below are those used by the Methow Beaver Project to process and 

handle beavers at the project’s beaver holding facility. Not every project will have such an 

ideal holding facility. Adjustments can be made based on available resources.

Animal Safety

Some basic practices can go a long way in protecting the health of the beavers, which is 

important. For example, working quietly and calmly can reduce stress to the animal, and 

keeping beavers properly restrained helps protect them—they may need protection from each 

other. It is important to properly sterilize your tools and injection sites. Also, if an animal 

appears to be suffering from great stress, it is appropriate to postpone the intake until later. 

Beaver Handling Precautions

Like most wild animals, beavers do not like to be handled and could bite if threatened. Also 

beavers can carry a variety of diseases. Caution is warranted when handling beavers to keep 

human contact as safe as possible. Be aware of the potential to be bitten during all transport 

and handling. A restraint bag is a good tool to keep beavers and humans safe during 

handling, tagging, and examinations. If you are bitten while working with beavers, clean the 

wound carefully and immediately notify your supervisor. Additional wound management 

may be necessary. 

 Wear exam gloves during all beaver evaluations, PIT tagging, ear tagging, and sexing.

 When tagging, prep skin on tails and ears with alcohol to reduce bacterial infection.
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 Always wear personal protective equipment (PPE) (i.e., waders) in raceways. 

 Limit the exposure of wounds on hands and arms to water in the raceways.

 Don’t eat, drink, smoke, or touch your eyes, nose, or mouth after handling beavers, their 

traps, or working in their environment until you have thoroughly washed your hands.

 If you become ill (fever, aches, swollen glands) during or after the project, report to your 

supervisor, see your physician, and inform them that you have been working with beavers 

and that bacterial infection could be the cause of your discomfort.

 If a beaver appears injured or sick, it should be placed by itself and watched carefully. Do 

not tag or sex any beaver unless it seems well. Beavers that seem unwell should not be 

used in a reintroduction project. Instead, consider (1) attempting to support the beaver’s

recovery in an isolated raceway for a few days, or (2) euthanizing the animal for humane 

reasons and to protect captive and wild beavers.

 Avoid dissection or necropsy. Necropsies need to be conducted by qualified veterinarians 

at appropriate facilities. 

 Regularly disinfect vehicles, traps, and gear—especially after handing sick beavers. Rinse 

traps, boots, tools, and food bowls with Virkon TM every week. This is a disinfection best 

management practice.

 Dry and expose raceways and houses to sunlight between occupancy.

 Work with state wildlife veterinarians to identify potential beaver disease issues. This 

includes shipping recently deceased beavers or tissues.

Assigning a Unique Identification Number

The first step in processing captured beaver is to assign a unique identification number (ID) to 

each individual. The Methow Beaver Project also inserts PIT tags into all captured beaver, so 

the first step is to determine whether the animal is a recapture by carefully scanning its tail 

with a PIT tag reader. This can usually be done while the beaver is still in the trap, when it 

arrives at the holding facility. 

The beaver ID is a combination of several items together. First is the two-digit year of capture 

(i.e., “13” for beavers captured in 2013). The second is the four-digit capture location. All 

beavers captured at a particular location will have the same location ID. For example, beavers 

captured at Pearrygin Lake have the code “PEAR.” If you are trapping at a new location, try to 

pick a four-digit ID that will make sense in the future. Often this is the landowner’s name 

abbreviated. The last part of the ID is the sequential number of capture, which increases by 

one every time a capture occurs. For example, a beaver captured at Pearrygin Lake in 2013 

following beaver number 212 would be 13PEAR213. 
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Special Notes on Recaptured Beavers

Recapturing beavers is not uncommon. The Methow Beaver Project recaptures several beavers 

each year, often many kilometres from their previous capture site. If a beaver has a PIT tag or 

ear tags, it is a recapture. The PIT tag number can be used to identify the beaver with the help 

of the PIT tag spreadsheet, computer records, or a printed copy of capture records (in the 

intake log). Once a beaver has been assigned an ID, that number stays with the beaver for life. 

The Methow Beaver Project typically keeps the intake forms from previous years on file in its 

office to reduce clutter in the field and protect the forms. For this reason, a new processing 

form should be filled out for a recapture. This also allows anything that may have changed, 

such as weight or tail damage, to be noted. The back of the intake form has a table to keep 

track of recaptures and observations of PIT tags by the instream fish PIT tag arrays. Any new 

capture information should be added to this table on the old form in the office. The paperwork 

should ultimately be stapled and filed together. 

Weighing Beavers

After an ID has been assigned, the beaver is weighed. The beaver should be kept in the trap as 

it is hung on the scale at the holding facility. Keep hands off the trap and weigh it several 

times, until a consistent number is reached. Subtract the trap weight and record the number. 

Snared beavers will have to be weighed by the difference in an appropriate enclosed 

container, probably the transport cage. 

Collecting Beaver Hair Samples

The Methow Beaver Project takes a hair sample from every beaver captured. This usually is 

done at the same time as ear tagging. Hair samples originally were collected to verify sex 

using mitochondrial DNA, but now the sample is taken because it is useful for future studies. 

The hair sample should be taken in such a way as to prevent cross contamination with human 

DNA or any other contaminants. While the beaver is in the Hancock trap, grasp a lock of hair 

with pliers and quickly tug it out. You want to get both guard hair AND underfur, to ensure 

that you collect hair follicles with the sample. Place the hair sample into a small manila (coin) 

envelope with the pliers. Do not mash the hair around with the pliers or stick your fingers into 

the envelope. Staple the envelope and write the beaver ID and date on the envelope. Between 

samples wipe the pliers thoroughly with a 95 percent ethanol solution to avoid cross 

contamination. The Methow Beaver Project stores hair samples in a clearly labeled Ziploc bag 

in a freezer until they are delivered to the U.S. Forest Service Wildlife Genetics Laboratory in 

Missoula, Montana. Many western beaver project DNA samples are being collected and 

catalogued there for future study. 

Ear Tags for Beavers

Ear tags (the Methow Beaver Project employs Floy tags) are used to quickly and easily identify 

captive beavers in the holding facility (Figure 16). They are not designed as a permanent 

marker because they do fall out naturally and get pulled out by beavers. They are color coded 

to correspond with the beaver ID capture number. 
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Figure 16: Floy tag being attached to a beaver held in a Hancock “suitcase” style trap. Photo credit: 

Methow Beaver Project.

Beaver Bags

Once the beaver has been weighed and ear tagged and a hair sample has been collected, 

everything else is done from the posterior of the beaver, with the animal restrained in a 

“beaver bag.” If you cannot obtain a beaver bag, you can sew a large bag out of a 45°-45°-90°

triangle of Cordura cloth. Sew the bag so that it remains open on one end adjacent to the 90°

corner with a small breathing hole in the opposite 45° corner. 

To get the beaver into the bag, place the beaver in its trap into a dry raceway to prevent escape

during transfer. Prepare all materials you will need to finish processing before transferring 

beaver to the bag. Open the Hancock trap and place the beaver bag over the open end of the 

trap. Lower the trap to its side and lay the bag out so the beaver can crawl into it. Laying the 

trap folded-frame-side down is awkward but allows the beaver to “step up” out of the trap; 

this can be useful, especially with larger animals. Extend the bag so that the beaver can see the 

breathing hole—“the light at the end of the tunnel.” Minimize any rustling of the bag’s 

Cordura material because this is a frightening sound to many beavers. As the beaver enters 

the bag, use your hands outside the bag to guide the animal into the end and prevent it from 

turning around. The beaver will squeeze down into the end. An assistant can hold the beaver 

in the bag while you work (Figure 17). 
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Figure 17: Workers transferring a beaver from the Hancock trap to a beaver bag. Photo credit: 

Methow Beaver Project.

Photographing Beaver Tails

Move the bag away from the tail and take a digital photo of the dorsal side of the tail. Record 

the picture number on the intake sheet. This may be useful data and help with future 

identification (Figure 18).

Figure 18: Photograph of a beaver tail, showing distinctive markings that are useful in identification.

Photo credit: Methow Beaver Project.
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PIT Tagging Beaver

PIT stands for Passive Integrated Transponder. The Methow Beaver Project injects PIT tags 

internally under the skin on the dorsal side of beaver tails. Although other projects tag 

elsewhere on beaver bodies, the Methow Beaver Project chose the tail to increase the chances 

that the PIT tag will be read by in-stream readers. 

About the size of a grain of rice, the PIT tag consists of inert wire, a chip, and a capacitor 

encased in glass. When a scanner is passed over the site where the PIT tag was injected, the 

radio frequency of the scanner will excite the PIT tag, which in turn will reflect the radio 

waves back to the scanner. In this way, the scanner can detect the unique alphanumeric code 

of the PIT tag. The main benefit of using PIT tags for marking beavers is that the tag is 

permanent (although some loss of PIT tags can occur). Additionally, detection arrays are 

located in waterways throughout the Columbia Basin, and all data are shared in the PTAGIS 

database online, from all agencies that maintain readers. This allows an organization or 

agency to search for PIT tags from its beavers anywhere in the Columbia Basin. It is critical 

that the tags be placed carefully, and that the number be recorded accurately. 

The PIT tag procedure is not necessarily difficult but it can be challenging to master. Use 

sharps safety, and consider practicing ahead of time on an orange. However, be aware that a 

beaver tail is quite tough (especially if the beaver is large) and that nothing will quite replicate 

the controlled force required to properly inject a PIT tag into a beaver tail (Figure 19). 

Figure 19: PIT tagging a beaver. Photo credit: Methow Beaver Project.
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Beaver Sexing

Sexing beavers is a key part of successful beaver restoration. Accurately sexing beavers helps 

with the following:

 Reducing peer-induced conflicts and death in captivity

 Raising the chances that breeding colonies will become established

 Predicting whether beavers will remain at a trapping location

 Inferring the demographics of beavers in the watershed

Sexing of lactating or reproductively receptive females can be done by simply checking for 

enlarged teats, but it is recommended that the sex be confirmed by examining anal gland 

secretions as well.

Sexing beavers is done while the beavers are restrained in the beaver bag, by manipulating the 

cloacal area and examining anal gland secretions (Figure 20). Schulte and others (1995) 

originally published this technique, which Dr. Lixing Sun demonstrated at the Methow Beaver 

Project facility in 2011. A beaver’s two anal glands are located inside the cloaca on the left and 

right, slightly anterior of the vent. They need to be manually pressed out of the vent and 

“milked” gently to yield secretions for examination. This is a tricky, slippery, and somewhat 

messy process—one that gets easier with practice.

Figure 20: Sexing beaver. Squeezing a beaver for oil gland secretions (male). Photo credit: Methow 

Beaver Project.
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You and your assistant should wear gloves for this procedure. Have your assistant cradle and 

restrain the beaver on its back, in the bag. Beavers do not like to be on their back and will 

thrash around if you let them. Cradling, as with an infant, can be effective. You may be able to 

kneel on the ground and position the beaver on its back with its tail away from you and its 

body resting on your thighs. The cradling method is by far the safest for most animals.

Once you have clear, stable, and unimpeded access to the cloaca, press your fingers GENTLY 

along the exterior of the vent, just anterior to and to the side of the vent. You should feel a 

lump. Pressing too far forward may cause castor oil—a thin, brown strong-smelling liquid—to 

be expressed. (If this accidentally occurs, you may wish to save it on cotton balls to use as a 

trapping lure). In addition, force applied in the wrong area—i.e., too far forward or too 

centrally—may cause the beaver to excrete feces or gas. Obviously this procedure should be 

done with your face a reasonable distance from the cloaca, with your mouth shut. You may 

also want to wear safety glasses.

When you feel one of the anal glands (either one is fine) you can direct it to emerge from the 

cloaca for manipulation. The gland looks like a swollen bulb with a pointed tip. It usually is 

quite slippery and has a few hairs at the tip. Continue to use one hand to maintain the same 

steady, gentle pressure you have used so far. Use your other hand to massage the gland to get 

the secretion from the tip. Steady, firm, and gentle pressure may work, or perhaps a milking 

motion. You will need to vary your technique to find what works best for you, and some 

animals will be easier to work with than others. Be patient and gentle; the animal under your 

care needs to be protected. It may happen that the anal gland withdraws and you will need to 

start over multiple times. Once some of the secretion has been emitted, wipe it onto a clean 

finger on your glove for inspection and compare to the chart in Table 8. 

Table 8: Indicators for Determining the Sex of a Beaver (from Lixing Sun, unpublished)

Male Female

Color Yellowish brown Whitish

Viscosity Thicker, Thinner, 

Odor Smells like petroleum (motor) 

oil

Smells like funky cheese

Use a combination of the indicators in Table 8 to make your determination as to the sex of the 

animal. Relying on just one indicator increases the chance of a mistake. Remember that these 

are general guidelines, and that individual animals can differ, although the color and odor are 

quite distinct and probably the best indicators. 
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Figure 21: Differentiation of oil gland secretions between the sexes. Photographs courtesy of Dr. 

Lixing Sun.

The sexing process may need to be repeated for a good sample to be obtained. Have your 

assistant evaluate the sample as well. The two of you should make independent decisions 

about the sex of the animal before comparing answers. It is better to admit that you cannot tell 

than it is to make unsure decisions. Try again, later if necessary. This technique, when done 

correctly, can give you an unmistakable sex identification (see Figure 21). 

Releasing Beaver at the Holding Facility

Putting the beaver into a detention area at the holding facility is the next step. First though, 

double check your intake sheet, because now is the time to catch omissions and errors, not 

after the release. The person already holding the beaver can bring the animal to the water and 

let it go, or hand it off carefully to someone else. Place the beaver bag into the water and pull it 

off the animal carefully. If necessary grasp the beaver by the base of the tail to pull it out of the 

bag. Do not drop the beaver from any height into the water. Always place the animal gently. 

When the Methow Beaver Project builds beaver groups in the holding facility for release, 

every situation is a bit different. Which beaver to release with which is important, as is 

monitoring the beavers immediately after release. Here are some general guidelines for 

successful beaver “matchmaking”: 
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 Consider keeping family groups intact. This usually is a good way to go, but family 

groups still should be observed. 

 Keep an eye on the beavers’ initial meetings and subsequent interactions until you are 

confident that they are friendly with each other. 

 Position yourself in the water where you can act quickly to physically separate 

beavers—safely—if necessary. 

 Release beavers into the water, so that any victims of aggression can flee quickly. 

 Give stressed beavers time to calm down; this may be necessary before their true 

reactions can be observed. 

 Protect kits from aggression, including from their parents. Kits are especially 

vulnerable to attack. 

 Remove the aggressor, not the victim. 

 Use caution when placing unrelated males together. 

 Have multiple houses available for the first night or two, so that if a beaver is rejected 

from a lodge it has another place to sleep. 

 Observe whether beavers that arrived at the holding facility at different times are 

lodging together. 

 Take good notes on unusual interactions. 

 Make sure you know who is who before releasing. 

Feeding Beavers While They Are Being Housed

Because captured beavers likely have been without food (and water) for some time, the 

Methow Beaver Project provides food right away. Food for beavers is delivered daily, at the 

end of the day (i.e., the beginning of the day for beavers). The Methow Beaver Project uses 

Mazuri Rodent Pellets because this product is high in protein and nutrients, is easy to acquire 

at the local feed store, and is one of the best foods beaver can receive (according to 

professional beaver keepers at Northwest Trek in Puyallup, Washington). The Methow Beaver 

Project also feeds beaver small amounts of apple and carrot. Apples are high in glucose 

therefore too sugary to serve as a main food for beavers, but supplementing with apples is a 

good way to get beaver to reach into the food bowl where the pellets are. Beaver should be 

given as many aspen and willow branches as they want. Fresh-cut green alfalfa is a good 

herbaceous supplement. 

Ravens and crows like the rodent pellets (and other food), so late evening delivery helps 

ensure that it is the beavers that get the food. Ideally, food amounts are such that most of the 
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food is gone by morning (this can take some adjustment) which avoids waste. It is essential 

that any wet food be cleaned from the bowl regularly.

Condition Notes for Each Beaver

Condition notes are a good way to keep track of the health, behavior, and location of each 

beaver. Condition notes should be made in a binder that stays at the holding facility at all 

times. Notes should describe diet (i.e., whether, when, and what the beavers are eating), 

behavior, and any injuries. 

Keeping track of each beaver’s health is critical. Individual beavers tend to behave differently 

from each other, so it’s important to get to know each of them so that you can recognize when 

they aren’t acting normally. Condition notes are especially helpful for weekend feedings, 

when you are observing. Communicating with your crew any concerns you may have about a 

beaver’s health is extremely important. 

The binder should be used to make good notes when you are moving beavers from raceway to 

raceway. To make sure you are moving the correct beaver, double check the ear tags and pit

tag. The binder also is a place to record how well individual beavers are getting along (e.g., are 

they sleeping in the same house?). This information is important in figuring out whether 

specific beavers are going to do well together when they are released. 

The Beaver Whiteboard 

The Methow Beaver Project uses a whiteboard to keep track of which beavers are in each 

raceway. The whiteboard shows the four raceways and each beaver’s ID, sex, and ear tag 

color. The whiteboard is helpful as long as it is kept up to date.

Beaver Release Site Preparation

Predation has been documented as a key impact on reintroduction success (McKinstry and 

Anderson 2002, Petro 2013). Finding ways to reduce exposure to predation losses is a 

reasonable objective for many restoration projects aiming to improve their results. 

The Methow Beaver Project has attempted to provide an initial period of security and calming 

for beavers immediately after they are delivered to sites by constructing temporary housing

from downed material adjacent to the release stream (e.g., see Vore 1993)(Figure 22). The 

concept in the Methow has been to provide a dark, quiet space covered with sticks and logs

about the size and volume of an overturned bathtub, next to the water, and in contact with the 

soil. Additionally, it can create a sense of familiarity if a deep layer of wood chips and sticks,

bedding from the holding facility, is placed within the hollow area, so that the space has the

odor of the beaver’s recent home, along with a small amount of the commercial food the 

beavers have been eating recently (large amounts may attract unwanted animals). These types 

of site preparations may encourage the beavers to give their release site a second look.
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Figure 22: Construction of an artificial beaver lodge in the Methow Valley, Washington. The lodge 

opening faces the water and is about 10 feet away from the water’s edge.

Another method the Methow Beaver Project has explored is to build an “awning” of sticks 

over the water connected to the structure that provides beavers overhead cover while in the 

water adjacent to the artificial lodge.

A key habitat feature at release sites is the availability of water deeper than 1 meter. Beavers 

need this for security and to eliminate body waste. Enhancing pools could substantially 

improve the likelihood that the released beaver will establish a colony. Where feasible, using 

beaver dam analogues (see Section 7) to create pools where none previously existed could 

substantially enhance the attractiveness of release sites and thus increase the number of 

reaches where beaver restoration can be considered.

Transportation and Release of Beaver

There is much to learn about enhancing establishment success by modifying release methods. 

Some literature recommends releasing beavers in the fall, when site construction is urgent 

(Vore 1993, Cramer 2012); however, the Methow Beaver Project, the Yakima Beaver Project 

(Meyer and Babik personal communication), the Skykomish Beaver Restoration Project 

(Schilling and Dittbrenner personal communication), the Grand Canyon Trust Beaver project 

(Christensen personal communication), Wildlife 2000 (Tippie personal communication), the 

Colville Beaver Project (Desautel personal communication), and others have experienced 

successful establishment in all months of the year during which releases have occurred. All 

have also experienced abandonment during the same months. This suggests that other factors 
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are more important to eventual success than the timing of the day, season, distance travelled, 

weather on the release day, food provided the day before release, etc.

Of greater significance may be the controllable site factors such as protection from substantial 

livestock overgrazing and trampling, proximity to roads and human infrastructure, beaver 

removal by recreational trappers, and unwelcome conflicts with adjacent landowners. 

Exposure to stochastic events such as fire, flood, and predation may also influence the success 

of beaver relocation efforts (Figure 23, transporting a beaver).

Delivery in metal transportation cages (Figure 23), wooden boxes, burlap sacks, and pet 

kennels (Figure 24-left photo)—by vehicle, game cart, backpack, horseback, ATV, and even 

crates thrown from aircraft (Heter 1950)—have proved successful delivery methods for 

beavers.

Figure 23: Transporting a pair of beavers to a new release site in the upper Methow River watershed, 

Washington. 2009. Photo credit: Methow Beaver Project.

The bottom-line take-home message from the last 80 years of beaver relocation efforts is that 

beavers are flexible, productive, tolerant animals that can adapt to new situations and 

locations and respond to a variety of situations to set up a colony and thrive—as long as basic 

woody building material and food, herbaceous food, and constant clean water are available 
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and population limitation pressures of disease, human interactions, and predation are not 

extreme.

Follow-up Beaver Monitoring and Support

Visiting the release sites frequently and providing appropriate follow-up support can 

encourage beavers to remain at the site, but this, too, is an area for further investigation. It is 

very difficult for humans to evaluate or monitor the exposure of release groups to predation 

pressure at a particular site. For example, although augmenting the existing sources of 

building material and food can be beneficial, there is also the risk that doing so will attract

unwanted animals or draw beavers to places where they are more exposed to predation. 

If you do decide to provide follow-up support, aspen or another local favored woody food is 

least likely to attract bears and can be used both as food and for construction of lodges and 

dams (Figure 24). It is easy to tell at the next visit whether the supplementary material has 

been moved or chewed, which would indicate ongoing beaver activity. If there is no indication 

of activity, the site can be supplemented with additional beavers.

Figure 24: (left) Releasing beaver, and (right) bringing a long-term food supply for relocated beaver in 

the BLM Green River Ranger District, Wyoming. Photographs courtesy of Kevin Spence.
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Risks Associated with Beaver Relocation Projects

Project Failure

Most beaver relocation projects have establishment success rates that generally do not exceed 

50% (McKinstry and Anderson 2002, Babik and Meyer 2013, Hoffman and Recht 2013, Petro 2013, 

Methow-Beaver-Project 2014) which means that many release attempts will not be successful

and that repeated attempts may be needed for beaver to colonize a site. This is normal. 

Additional cautions include the fact that beavers are very mobile. They can move offsite and 

completely disappear, or they may show up and build dams where they are not wanted. 

Identifying the precise factors that cause beavers to “stick” continues to be difficult. Projects 

that have had success emphasize the value of persistence and patience.

Additional Risks: Parasites and Disease

Like other wild animals, beavers as a group carry parasite and disease loads that are part of 

their ecology. Some aspects of beaver parasites and diseases have been studied, but there is

much to learn about how relocation efforts influence these factors for beaver populations.

Tularemia, yersinia, rabies, and leptospirosis are some of the diseases noted in wild beaver 

populations. In 8 years of sampling and monitoring, the Methow Beaver Project has 

encountered two cases of tularemia and one case of yersinia infection in captured beavers (K. 

Woodruff, personal observation). The subject beavers died in captivity and were necropsied at 

the Washington Animal Disease Diagnostic Laboratory; subsequent testing was conducted at 

the National Wildlife Health Laboratory. In discussions with Washington State health officials, 

they acknowledged that these diseases are naturally present in most wild animal populations, 

not just beaver (K. Woodruff personal communication). 

Giardiasis is a chronic, intestinal protozoan infection seen worldwide in most domestic and 

wild mammals, many birds, and people. Although most people associate Giardia lamblia

intestinal infection with beavers, the protozoa is commonly found in most waterways in North 

America and occurs in a percentage of most wild and domestic animals and humans across 

the globe.

Beaver can carry the rabies virus, and, although rare, attacks on humans by rabid beaver do 

occur. Beavers acting aggressively or erratically should be avoided.

Wild beaver may also carry ectoparasites, such as the beaver beetle (Platypsullus castoris), the 

North American beaver beetle (Leptinillus validus), and several species of beaver mites 

belonging to the genus Schizocarpus. None of these ectoparasites presents a risk to humans or 

beavers.

In summary, precautions against infection are necessary for everyone who handles beavers. 

Any beaver relocation project should implement safe handling and sterilization policies to 

protect crew members and limit the potential spread of disease.
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Chapter 6—Beaver Dam Analogues (BDAs)

Michael M. Pollock, Nick Weber and Gregory Lewallen

Beaver dam analogues (BDAs) are channel-spanning structures that mimic or reinforce natural 

beaver dams (Figure 25). As such, they are semi-porous to water, sediment, fish and other 

water-borne materials. Like natural beaver dams, BDAs are biodegradable, temporary features 

on the landscape with functions that change in response to the effects of flowing water, 

sediment, and beaver activity (Pollock 2012). Also like natural beaver dams, BDAs function 

best when constructed in sequence, such that the structures work in concert with each other. 

Beaver dam analogues are constructed with material that is similar to what beaver use to build 

their dams. Depending on what type of BDA is constructed, this may include sediment 

ranging in size from cobbles, gravel, sand, silt and clay, vegetation such as the stalks of 

emergent vegetation, the branches and stems of decidous trees and shrubs (usually willow or 

cottonwood) and wood posts made from the boles of conifers (Figure 26). A complete 

construction sequence for a BDA would be to first install a line of posts using a hydraulic or 

pneumatic post pounder (Figure 27), followed by weaving branches in between the posts. An 

upstream face is then constructed first using cobble and other large material placed at the 

upstream base to prevent underscour, followed by successive layers of vegetation and finergrained material until the structure has achieved the desired level of flow permeability and 

upstream pool depth. 

Background

Beaver dam analogues are the latest iteration in a long history of constructing channelspanning structures for the purposes of restoring stream habitat. Past efforts include 

construction of wire cages filled with rocks, rock dams, rock dams with mortar, boulder weirs, 

and channel-spanning logs and log steps (Slaney and Zaldokas 1997, Flosi et al. 2010, Cramer 

2012). Key to the successful application of any of these techniques is understanding how they 

affect the transport of sediment and water, and how such effects vary depending on where 

they are placed within a watershed. Thus, understanding the hydrogeomorphologic context 

within which such structures are placed will have a tremendous effect on project success. In 

the case of BDAs, success will be determined largely by the selection of a suitable location for 

the structure, and less so on the relatively simple construction techniques. Chapter 5 describes 

the planning framework for identifying suitable locations within a watershed. 

The addition of BDAs to a fluvial ecosystem with beaver should increase both the abundance 

and life span of natural dams, which in turn should promote reconnection of floodplain 

surfaces and an overall increase in both instream and riparian habitat heterogeneity and 

quality. Such longer lived, less transient dams should become building blocks for resilient and 

dynamic beaver dam complexes that support thriving colonies of beaver.

Although resilience and dynamism may seem at odds with each other, it is natural for activity 

in beaver dam complexes to ebb and flow (Naiman et al. 1988b, Pastor et al. 1993, Burchsted et al. 
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2010). Individual dams within a dam complex may be washed out or abandoned, but the 

importance of individual dams is not as critical as the combination of multiple dams within a 

broader dam complex. Individual dams can serve different functional purposes or be at 

different stages in their trajectories. The significance of the failure of an individual dam in a 

dam complex is much less than that of an isolated beaver dam. The resilience of a dam 

complex lies in its ability to maintain a healthy and stable system state (i.e., population) 

despite disturbances or external forcings. If other suitable locations are available, a colony may 

also be able to retain resiliency by shifting to a new location and abandoning a dam complex 

when its functionality decreases (Naiman et al. 1988b, Burchsted et al. 2010). This leads to a 

dynamic, shifting habitat mosaic in time and space (Tockner and Stanford 2002) that should 

promote habitat complexity and resilience for beaver and species that benefit from the beaver 

dam complexes.

Figure 25: Examples of beaver dam analogues in Oregon and California.
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Figure 26: Diagram of a starter dam, showing design detail and the necessary material needed for 

construction. (top) side view (bottom) plan view.
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Figure 27: Hydraulic post pounder options. Options include, clockwise, starting from upper left: 

(a) a hand-held pounder attached to hydraulic power pack, (b) a post pounder attached to 

bulldozers, (c) a handheld pneumatic post pounder attached to an excavator and (d) a modified 

excavator with a vibrating pad. Options (a) and (b) take approximately 5 to 10 minutes per post, 

depending on substrate, and it can be difficult to get to the desired depth. Option (d) takes less than 

1 minute per post and can drive posts as deep as needed. All pounders have a metal cylindrical cap 

that holds the post in place while pounding. Each option has pros and cons to consider, including 

cost, maximum depth the posts can be pounded, substrate type, operator strength and expertise, and 

the amount of likely riparian and instream disturbance. Photo credits: (a) Nick Weber, Ecological 

Research, (b) Mark Cookson, USFWS, (c) Peter Thamer, Siskiyou County Resource Conservation 

District, and (d) Julie Ashmore, Okanogan Highlands Alliance.
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Typical Successional Trajectories and Outcomes for BDAs

Because BDAs are designed to mimic natural beaver dams, some key considerations need to 

be incorporated into their design. Like pools caused by natural beaver, pools upstream of 

BDAs go through a sequence of changing habitat types, with the rate of change and 

successional trajectory depending largely on stochastic processes, such as flooding, sediment 

transport, and beaver activity, as well as the hydrogeomorphic setting. 

In general, like natural beaver dams, BDAs that remain intact form a pool upstream that fills

with sediment over time. As the sediment accumulates, it is colonized by emergent and 

riparian vegetation and transitions from an open pool to an emergent wetland and eventually 

to a wet meadow that may or may not contain a definable stream channel. At each step in a 

successional trajectory, both natural beaver dams and BDAs can fail, altering the successional 

trajectory and creating different successional trajectories depending on the failure mechanism. 

Failed dams can also be repaired, creating additional successional trajectories. Thus there are 

multiple successional trajectories that BDAs can take, which are not predictable in a 

deterministic sense because of the stochastic nature of the mechanisms that can trigger 

alternative pathways. 

Because BDAs are intended to mimic beaver dams, they require ongoing maintenance and 

repair, similar to beaver dams. The amount and type of maintenance needed depends on 

project objectives. Typical maintenance includes extending the length of the structure as a 

result of end cutting, replacing sections that have been damaged (often from underscour), and 

raising the height of a structure, typically by constructing a new BDA on top of the sediment 

wedge that has accumulated upstream of an existing BDA (Figure 28).

By providing some short-term (i.e., less than 10-year) structural complexity in stream systems 

that generally lack structure, BDAs should set in motion natural processes by which the 

stream restores its natural dynamics. This is often the expected outcome of projects that use 

BDAs. BDAs should facilitate fluvial geomorphic changes that include sediment retention, 

streambed aggradation, increased stream sinuosity, pool formation, increased stream length, 

reduced stream slope, reduced bed shear stress, and a shift in the bed composition from 

coarser to finer sediment (Pollock et al. 2007, Demmer and Beschta 2008). Similar to beaver dams, 

BDAs should also raise water tables in the alluvial aquifer, thus helping to greatly expand the 

amount of riparian forest and reduce stream temperatures (Lowry 1993, Westbrook et al. 2006, 

Pollock et al. 2007; Weber et al. 2017). Previous research has shown that these are reasonable 

outcomes to expect from the presence of stable beaver dams, particularly in streams with high 

sediment loads (Scheffer 1938, Pollock et al. 2003, McCullough et al. 2005, Westbrook et al. 2011).
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Figure 28: Side view of beaver dam analogues designed to aggrade a bed within an incision trench. (top) 

Year one placement. The downstream BDA backs up water to the upstream BDA, forming a water 

“pillow” that helps prevent overtopping scour below the upstream structure. Willow branches can be 

placed parallel to the stream flow on the downstream side of a BDA to help reduce scour. The post should 

be placed deep enough in the ground to prevent structure failure as a result of downstream scour, 

although multiple posts woven together with willows can hold some scoured posts in place. (bottom) 

After sediment accumulates and aggradation occurs upstream of the BDAs, another round of BDAs is 

placed upstream of the existing BDAs, on the aggraded bed. Placement should be upstream such that the 

downstream sediment scoured is deposited against the BDAs installed in Year One; this helps to reinforce 

and strengthen the BDAs. The process can be repeated until the stream bed has aggraded sufficiently to 

reconnect it to its former floodplain.
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Uses for BDAs

Beaver dam analogues have several advantages over natural beaver dams. For example, 

because they are constructed using posts pounded into the stream bed, they are less 

susceptible to failure from overtopping flow than are natural beaver dams (overtopping flow

is a common failure mechanism for natural dams). Thus they can be placed in incised streams 

and other locations where the stream power per unit width is higher than what natural beaver 

dams would be able to tolerate. Another advantage of BDAs is that they can be placed at a 

specific location and designed to increase the likelihood of a specific outcome. Structure width 

and height can be controlled, and adjustments can be made as needed to facilitate restoration 

objectives. 

BDAs can be used to do the following:

 Create pool habitat (upstream and downstream)

 Improve floodplain connectivity

 Expand riparian vegetation

 Increase stream sinuosity

 Create multi-threaded channels

 Nourish streams with sediment

 Reduce bank erosion

 Establish beaver colonies

 Provide protection for relocated beaver

BDAs may be especially useful in incised streams where the steep banks confine the stream, 

thus concentrating stream power during floods. When placed in narrow, incised reaches, 

BDAs are often sufficient to reduce stream velocities, increase sediment deposition, and 

initiate aggradation. They can also be designed to direct concentrated flow to erode resistant

banks, widen the incised channel, and enhance the sediment supply to downstream reaches 

(Pollock et al. 2014).

Similar to the multiple dams found in beaver colonies, placement of multiple BDAs is critical

(Figure 29). Multiple placements will increase the overall effectiveness of the system and 

decrease the likelihood of failure during a large flood. With multiple structures, if one fails, the 

remaining BDAs still dissipate stream energy. As with natural beaver dams, when a BDA fails, 

it often produces more heterogeneous habitat (Denmer and Beschta 2008, Pollock et al. 2014). 

Types of BDAs

BDAs are intended to mimic the functions of natural beaver dams. There are several ways of 

constructing beaver dam analogues: (1) constructing starter dams using vertical posts with 

willow woven between the posts (wicker weave) and fill material (such as cobble, vegetation 

and mud) placed upstream to create a water-retaining structure, and (2) installing just post

lines with wicker weaves, which are highly permeable and may or may not initially retain 
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water, depending on stream discharge; and (3) simply reinforcing existing natural beaver 

dams with vertical posts, these common designs are discussed below.

Figure 29: Example of a sequence of beaver dam analogues on Bridge Creek, in Oregon. The primary 

dam is a reinforced existing dam originally built by beaver, while the secondary dams are post lines 

with wicker weaves that self-sealed with sediment and organic material. The primary dam has 

remained stable for more than 5 years and has created extensive flooded wetlands on river right. The 

secondary dams create pool habitat, dissipate energy, capture return flow, and raise water levels, which 

reduce the potential for headcutting on return flow side channels, while also increasing the floodplain 

inundation period. (Photograph and graphics by N. Weber).
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Starter Dams 

Starter dams utilize all the elements of BDA design, and are designed to immediately pool 

water upstream upon completion. They are constructed of vertical wooden posts that are 

pounded into the stream bed using a hydraulic post pounder (Figure 26) and typically spaced 

about half a meter apart. The posts then are interwoven with fresh branches or stems, usually 

willow (Figure 25). This creates a highly permeable dam that often does not restrain flow 

sufficiently to form a pool, at least in the short-term. When an upstream pool is immediately 

desired (e.g., if beaver are going to be released at the site, or there are beaver in the area and 

you are trying to entice them to establish a colony), permeability can be reduced by placing 

cobble, sand, silt, and vegetation on the upstream side of the starter dam, sufficient to form a 

pool of the desired depth (usually 1 meter or more). 

Starter dams are generally not as thick as natural beaver dams, particularly on the 

downstream side, and thus they are more prone to forming downstream scour pools that can 

lead to underflow failure (Figure 30). To minimize the potential for underscour failure, posts 

should be pounded into the substrate as deeply as possible, and sufficient material placed on 

the upstream side of the post line to prevent the upstream bed from mobilizing (Figure 26). On 

the downstream side, branches can be placed at an angle, perpendicular to the stream flow 

(similar to how beaver place branches), which also helps to minimize downstream scour from 

overtopping. For a given stream size, highly mobile beds (e.g., those containing limited 

amounts of cohesive, fine-grained material) will be more prone to underscour and require 

more material to prevent underscour from occurring (Figure 30). 

Scour failure can also be reduced by constructing structures such that they are connected to 

wide floodplains, at least during high flows. A well-constructed beaver dam will disperse flow 

evenly across its width, sufficient to reduce stream power per unit width so that flow is not 

concentrated and scour is minimized. This is a dam construction feature at which beaver excel, 

even compared to humans, and it illustrates why it is important to consider beaver as 

collaborators in restoration efforts. If beaver can be enticed to come to, or remain at, a project 

site, they will do a much better job than people will of maintaining structures, such that flow is 

more evenly dispersed across the entire width of the dam. Even if beaver are not 

(immediately) present, building structures that disperse flow across the floodplain helps to 

keep the structures from failing by creating multiple smaller “side” channels that lack the 

erosive power of a single larger channel. 

Floodplain connectivity is also important in ensuring that fish can pass beaver dams. 

Observations suggest that most fish cross beaver dams by swimming through or over the dam 

where water is flowing, or by swimming around the dam using side channels. Fish rarely pass 

over a beaver dam by jumping over in a single leap. The use of side channels and dam 

interstices explains how fish are able to regularly pass beaver dams that may rise as much as 6 

feet above the stream bed and may be 6 to 12 feet wide at the base (Figure 31).

Starter dams can fail when flow removes erodible bank material such that there is an “end 

cut” around the dam (Figure 30). The potential for end-cut erosion can be reduced by 
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extending the structure by wrapping the upstream banks using posts and wicker weave 

(Figure 29). These bank wraps are typically higher than the main portion of the structure so 

that flow remains in the main channel or is dispersed across floodplain side channels, without 

being concentrated on erodible bank materials.

Post Lines with Wicker Weaves 

Post lines with wicker weaves (PLWW) are constructed similar to starter dams but are left 

unsealed so that they are quite permeable to flow, at least initially (Figure 25). Ideally, PLWWs

naturally become less permeable over time as sediment and organic material transported from 

upstream sources accumulates, or because beaver occupy and maintain the structure. The 

advantage of PLWWs is that they require much less effort to build than starter dams do, so 

many more of them can be built for the same cost. They are particularly useful in streams 

where fine sediment loads are high (e.g., incised streams with cohesive fine-grained banks) 

and there is a reasonable expectation that they will self-seal as upstream sediment and organic 

material accumulate. 

Both starter dams and PLWWs work well when enough of them are placed near each other 

that the ponding from a downstream structure provides a “water pillow” below the upstream 

structure; this reduces the potential for scour and subsequent structural failure (Figure 27).

Placing several structures near each other thus provides stability, similar to how multiple 

beaver dams in a colony function together. If one structure fails, other structures may still hold 

and, overall, important ecosystem functions within the treated reach can be maintained.

Reinforced Existing Dams

The simplest type of BDA is to reinforce an existing beaver dam if it is in a desirable location. 

Existing beaverdams are reinforced by pounding posts vertically into the dam on the 

downstream side, 1/2 meter to 1 meter apart, and inserting them into the steambed as deeply 

as possible— preferably 1 meter deep or more, although shallower depths can still be quite 

effective.

Reinforced existing dams are usually more stable structures than BDAs that are primarily 

constructed by humans. This is because beaver generally use more material during dam 

construction than humans and beaver also create wider dams that are less prone to 

underscour. Also, if beaver are present, they will maintain reinforced dams, further ensuring 

stability. Common causes of failure of reinforced existing dams are side scour of erodible 

banks and failure from underscour or overtopping erosion. 

Not all existing dams should be reinforced. The decision to reinforce an existing natural dam 

usually is made when it is likely that the dam will fail sooner than desired, given the project 

objectives, or when the consequences of failure—even if unlikely—would be undesirable. For 

example, an existing beaver dam upstream of a culvert might be reinforced so that it won’t 

blow out and block the culvert with debris.

Like natural beaver dams, starter dams can fail during high flows, and they need to be 

inspected, maintained, and repaired if necessary. If beaver are present, they may do much of 

the repair work. It takes a certain amount of judgment to know whether and when to repair a 
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damaged structure. Damaged structures may still function, or they may have already achieved 

their desired purpose, or they may no longer be needed because their function has been 

subsumed by another structure. Natural dams fail but still function to increase habitat 

complexity, and this is also the case for failed BDAs. 

When placed within incision trenches, BDAs often end cut because stream power cannot be 

sufficiently dispersed. In these situations, it is reasonable to expect to repair such structures 

annually by extending them across the end-cut channel, either until sufficient aggradation has 

occurred upstream that flows are dispersed across a reconnected floodplain or until the 

incision width is sufficient to create a stable dam in the inset floodplain.
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Figure 30: Examples of beaver dam analogue failure mechanisms: (top) overtopping downstream 

scour followed by underscour; posts that are not pounded deeply enough into the bed deep can be 

undermined by overtopping downstream scour, and (bottom) lateral scour of an erodible bank 

results in an end cut.
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Figure 31: At nearly 2 meters height, this natural beaver dam on Bridge Creek, Oregon, substantially 

exceeded most fish passage guidelines for instream structures, which generally call for a maximum 

“jump” elevation of 15-20 cm between the upstream and downstream water elevations of a structure. 

Nonetheless, adults and juveniles of steelhead trout were able to pass the structure, as documented by 

PIT tag data, and there is a well-distributed population of steelhead upstream of this dam and the 

dozens of other dams further downstream. (Julie Maenhout is in foreground, photographer, unknown).

Effects of BDAs

The primary effect of BDAs is to reduce stream power per unit width by dispersing flow over 

a wider cross-section and through localized lowering of the slope; this greatly increases stream 

width and creates a hydraulically complex channel-spanning structure that causes turbulence, 

thus dissipating energy. As with natural beaver dams, the resulting benefits can be many and 

varied:

 Trapping of sediment

 Aggradation of incised channels

 Floodplain connectivity and creation

 Elevation of the water table

 Groundwater recharge

 Increased surface area for riparian colonization

 Increased aquatic habitat diversity
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 Increased avian habitat

 Increased wetland area

 Localized water temperature buffering

Some of the effects of BDAs can be more pronounced than those of natural beaver dams. For 

example, because BDAs are reinforced with posts, they tend to fail by end-cutting rather than 

overtopping erosion (Demmer and Beschta 2008). This means that, if they are strategically 

placed and designed, they have the potential to increase erosion in specific areas by

concentrating flow toward erodible banks. This may be desirable in channels in the initial 

stages of incision, where there is little or no development of an inset floodplain. Placing BDAs

to direct and concentrate flows in specific areas can help erode resistant banks and widen the 

active channel. Development of an inset floodplain, or widening the active channel, increases 

the amount of potential riparian habitat, lowers the unit stream power, and reduces active 

incision. Additional BDAs placed in the inset floodplain can cause the streambed to begin to 

aggrade, thus providing more suitable habitat for beaver.

Because BDAs tend not to be as wide as natural beaver dams, they also tend to create deep 

scour pools downstream of the structure. If posts can be inserted into the bed deeply enough 

that they are not undermined, these scour pools can be maintained and will provide deep 

pools with complex cover that are preferred by many fish species, particularly salmon and 

steelhead. In addition, the scouring action sorts and deposits sediment further downstream, 

potentially creating gravel deposits of sufficient size and calibre to support spawning. This 

may be particularly important in streams where the bed is armored with coarse substrate and 

there is limited bed mobility or sediment sorting.

Risks in Using BDAs 

Risks in using BDAs for stream restoration are limited. BDAs are inexpensive, so even if the 

structure is ineffective, or is washed out in a subsequent flood, the economic impact is low, 

especially when constrasted with other more intensive forms of stream restoration, such as full 

channel realignment. Also, because BDAs are small in size and use material similar to that in 

natural beaver dams, if the BDA fails there is less risk to downstream habitat or infrastructure 

than there is with other types of restoration projects, such as large wood placement. 

There is some risk that a series of ponds created by BDAs could increase stream temperatures 

enough to degrade habitat for fish, or that a series of structures could block the movement of 

fish enough to have a negative population-level effect. However, these risks need to be 

weighed against the likely benefits of BDAs in terms of the ecosystem functions targeted by 

the restoration project. For example, a beaver pond may have high temperatures in the 

summer and thus avoided by salmon and steelhead, but in the winter it provides critical 

juvenile overwintering habitat and holding pools for migrating adults. 

In incised streams, BDAs can initiate the process of restoration, but ultimate success often 

hinges on active colonization by both vegetation and beaver. Although artificial structures can 

cause rapid aggradation, vegetation is still needed to increase bank strength and surfaces and 

to provide shade, and beaver are needed to maintain and expand the BDAs. It also is 
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necessary to identify and eliminate the stressors that caused the initial incision to occur (e.g.,

livestock grazing in the riparian zone or extirpation of beaver) (Pollock et al., 2014).

Finally, as with natural beaver dams, BDAs are meant to be temporary features on the 

landscape and may breach or fail completely during high-flow events and contribute to flood 

peaks. On the other hand, using posts to reinforce existing beaver dams can reduce the 

potential for failure of dams in vulnerable sites, where failure could have severe consequences 

to downstream infrastructure. Also, the risk of downstream flooding is reduced when 

multiple BDAs are constructed in series. 

Both BDAs and natural beaver dams will increase the amount of surface water at a site in the 

form of pools, ponds, overbank flows, and side channels. This increase in surface water may 

flood areas that rarely flooded in the recent past. However, flooding of infrastructure, 

agricultural fields, or private property in low-gradient areas, floodplains, or on adjacent 

properties may not be a desirable outcome of the restoration action. In addition, riparian 

restoration and management can increase the hydraulic roughness of the stream bank and 

floodplain, thereby raising floodwater elevations (Kauffman et al., 1997). 

Careful placement and monitoring of BDAs will reduce the risk of inadvertent flooding and 

other beaver/human conflicts. In areas where inadvertent flooding is likely, restoration 

projects should be designed for continuity of flow and sediment. Such projects will necessarily 

provide less value to river ecosystems, but they will decrease the potential for damage to 

infrastructure that that is located on floodplains or in channels.

*************
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Chapter 7—Urban Beaver Population 

Management

Gregory Lewallen, Heidi Perryman, Kaegan Scully-Engelmeyer, Ellen Wohl

In this chapter, we discuss strategies and techniques applicable to managing beaver in urban 

settings and how beaver might be used as a restoration tool in such environments. These 

approaches have been utilized on various scales, from entire watershed management plans 

down to site-specific restoration projects. We use “urban setting” in this context as any aquatic 

habitat capable of supporting beaver in or around a city (i.e., city centers, suburban, and 

suburban fringe) where the primary source of conflict with a beaver-based watershed 

management strategy will be direct and indirect impacts on the built environment.

Introduction

The United States is becoming increasingly urban (Cohen, 2015), with nearly 81% of the 

population living in urban or suburban settings in 2010, up from 74% in 1980 (US Census,

2010). A variety of urban wildlife also inhabit these settings, which means that human 

interactions with wildlife are inevitable, and beaver are no exception (Soulsbury & White,

2015). In 2015, urban beaver incidents occurred in 39 states across the country (reported by 

Martinezbeavers.org; figure 32) This estimate is conservative given that many human-beaver 

conflicts go unreported. 

Figure 32: Urban beaver incidents reported across the United States
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As human-beaver conflicts increase, fish and wildlife biologists, restoration practitioners and 

land managers are considering alternatives to the historical approach of lethal removal. 

Increases in both human and beaver populations, positive shifts in public perception toward 

wildlife (Needham & Morzillo, 2011; Morzillo & Needham, 2015), and recognition of the

aquatic habitat benefits provided by beaver are helping this redirection toward non-lethal 

management (Pollock et al., 2012; Polvi & Wohl, 2013; Wohl, 2013). 

Because urban river and stream systems are often heavily degraded, modified, and 

contaminated (Nowell, 2001; Elmore & Kaushal, 2008; Roy et al., 2009), urban stream

restoration projects are typically expensive and do not always result in a significant increase of 

ecological benefits (Bernhard et al., 2005; Kenny et al., 2012; Bernhardt & Palmer, 2011; Stranko 

et al., 2012). However, partnering with beaver in urban stream restoration has the potential to 

be cost-effective, ecologically compatible, and successful because beaver are constantly 

responding to changes in their environment which is simply not feasible for most 

municipalities. 

Problematic behaviors often preclude beaver from consideration as a potential asset in urban 

settings. However, their ability to adapt to diverse habitat types make them a valuable species 

to consider in urban stream restoration. While there is broad recognition that beaver can block 

undersized culverts, flood roads, or harm landscaping, the ecological advantages are less 

apparent. A review of the literature confirms hydrological, ecological and sociological reasons 

to consider incorporation of beaver into an urban landscape. Modern tools for beaver 

management provide for this opportunity while concurrently maintaining public safety, 

infrastructure and landscaping (Callahan, 2005; Boyle, 2009; Tippie, 2010; Wheaton, 2013; 

Taylor, 2014; Portugal et al., 2015; Fitch, 2016; Lunquist & Dolman, 2016). 

Certain situations and habitat conditions, however, are not conducive for beaver 

establishment. Salisbury and White (2015) conclude that there will always be a need to 

manage wildlife populations in urban settings to reduce human-wildlife conflicts and to 

provide the missing natural forms of population regulation, such as predation. Careful 

consideration is warranted for balancing the benefits of accommodating wildlife with the need 

for minimizing the consequences for both people and animals. When the benefits provided by 

urban beaver outweigh the costs to a community, then beaver-based stream management 

options should be explored. An example from Martinez, California (see page 22) illustrates the 

myriad of community benefits derived from just a single beaver colony. However, relocating 

beaver to wilder places (see Chapter 5: Relocating Beaver) might be the preferred alternative for 

both beaver and people, as demonstrated by Wildlife 2000 in Colorado.

This chapter discusses the benefits and challenges of urban beaver, and illustrates successful 

case examples of mutually beneficial co-existence. Rather than simply managing beavers in 

urban environments, it may make more ecological and economic sense to integrate their 

presence as a form of natural habitat restoration.
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Benefits of Beavers in Urban Settings

Beaver dams in urban settings can provide benefits similar to those in rural areas, including: 

storing surface and groundwater, regulating flow, improving stream complexity, modifying 

nutrient cycling, storing sediment, and increasing biodiversity, while also restoring stream 

resilience (Naiman et al., 1986; Naiman et al., 1988; Baker, 1995, 2005; Butler & Malanson, 1995; 

Wright et al., 2002; Cunningham et al., 2006; Westbrook et al., 2006; Martell et al., 2006; 

Muskopf, 2007; Pollock et al., 2007; Hood & Bayley, 2008; Burchsted, 2010; Beechie, 2013; Smith 

& Mather, 2013; Lazar et al., 2015; Pollock et al., 2015; Law et al., 2016). Beaver modification of 

confined urban streams generally result in either single dam-pond pairs or a linear series of 

dams and ponds interconnected by sections of running water. This “step-pool” stream profile 

increases biodiversity and stream complexity because of increased hydraulic diversity, which 

is often desired in urban streams. For example, Law and others (2016) compared rural, 

confined streams of eastern Scotland modified by beaver (Castor fiber) to unmodified reaches. 

Their results indicate that at the catchment scale, beaver modifications increased physical 

heterogeneity, attenuation of peak flows, and significant reductions of both phosphorus and 

nitrogen (49% and 43% respectively). Furthermore, the changes in invertebrate richness at the 

landscape scale increased by an estimated 28% in the presence of beaver.

Biotic and Abiotic Benefits

Beavers are considered “ecosystem engineers” because of their ability to create diverse 

habitats for themselves and other organisms. The spatial heterogeneity of sediment and 

moisture content within a beaver meadow creates habitat for a much broader array of plant 

species than are found in adjacent uplands or in portions of a river without beaver activity 

(Wright et al., 2002). These diverse plant species in turn support a much greater abundance 

and diversity of animals that spend most or all of their lives within the river corridor (e.g., 

fish, frogs, turtles) and animals that use the river corridor during specific times of the year or 

specific periods of their life cycle (e.g., migratory birds, reptiles, mammals). Most organisms

studied in the context of beaver-modified habitat– including plants, bacteria, aquatic insects, 

butterflies, amphibians, and fish –have greater abundance and diversity than adjacent uplands 

or portions of the river corridor without beaver activity (Rolauffs et al., 2001; Pollock et al., 

2003; Bartel et al., 2010; Hood & Larson, 2014; Hossack et al., 2015). Species biodiversity and 

abundance in urban settings translates to enhanced recreational opportunities such as fishing, 

bird watching, and photography. Greater biodiversity also typically equates to greater ability 

of plant and animal communities to recover following a natural (e.g., flood, drought) or 

human-induced (e.g., chemical spill) disturbance to the river corridor (Tilman, 1996; Doak et 

al., 1998).

Water -- Beavers are recognized as ecosystem engineers primarily because of the effects of 

their dams on the movement of water along river corridors. By obstructing flow, a beaver dam 

creates a pond, which is the most obvious effect; however, dams also promote overbank flow 

during high discharge. Some of this overbank flow may concentrate in depressions on the 

floodplain, particularly where beavers have excavated a network of small canals. 

Concentration of water within a portion of the floodplain increases the erosive energy of the 

water and can form a network of secondary channels that branch from and eventually rejoin 

the main channel (John & Klein, 2004; Polvi & Wohl, 2012, 2013). Some of the overbank flow 
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facilitated by beaver dams can also infiltrate into the floodplain, which helps maintain a 

higher water table (Westbrook et al., 2006) that favors riparian and wetland plants, such as 

willows, alder, river birch, and cottonwood. 

Beaver ponds increase pressure gradients along the streambed which force water into the 

channel bed (Lautz et al., 2006; Janzen & Westbrook, 2011). Water enters the hyporheic zone,

the area immediately below the surface of a channel, through the bed and generally flows 

downstream and across valley bottoms. Water reemerges into the stream through upwelling,

or into the floodplain as seeps and springs. Hyporheic exchange reduces the sediment 

suspended in the water, moderates water temperature fluctuations, and typically removes 

dissolved and particulate nitrogen, phosphorus, and carbon (Tonina & Buffington, 2009).

Alterations in surface and subsurface pathways of water as a result of beaver dams have the 

net effect of reducing the magnitude of moderate flood events by storing water in ponds and 

floodplains, which is then released more gradually following the flood peak (Puttock et al., 

2016). Whether the flood results from a single rainstorm or represents annual snowmelt over a 

period of weeks, beaver meadows attenuate the downstream fluxes of water, sediment, and 

organic material so that flood peaks are not as high and base flow is not as low.

Decades of research regarding microclimates under forest canopies have been augmented by 

additional research on riparian zones. According to Moore and others (2005) “compared to 

open environments, the canopy reduces solar radiation, precipitation, and wind speed near 

ground level and increases longwave radiation received at the surface. These changes in turn 

influence the thermal and moisture environments under forest canopies.” By increasing the 

amount of ponded water, saturated soil, and dense vegetation, beaver can increase both 

evaporation and evapotranspiration (Woo and Waddington, 1990). This can create a 

microclimate of cooler, moister air along the stream corridor that can provide noticeable relief 

from summer heat within ‘urban heat islands’ and provide a warmer environment during cool 

winter months. This moderating effect is particularly important in urban areas because the 

urban heat island effect often has detrimental impacts to aquatic systems. Somers and others 

(2013) found that “streams draining urban heat islands tend to be hotter than rural and 

forested streams at baseflow because of warmer urban air and ground temperatures, paved 

surfaces, and decreased riparian canopy. Urban infrastructure efficiently routes runoff over

hot impervious surfaces and through storm drains directly into streams and can lead to rapid, 

dramatic increases in temperature. Thermal regimes affect habitat quality and biogeochemical 

processes, and changes can be lethal if temperatures exceed upper tolerance limits of aquatic 

fauna.” Thus the introduction of beaver into urban streams may help moderate the negative 

urban heat island effects.

Peer-reviewed literature on the impact beavers have on the hydrology of urban catchments is 

limited. However, recent research from an intensively managed grassland stream located in 

Devon, England, may offer similarities to confined and modified urban and suburban 

catchments. Puttock and others (2016) found that a reintroduced pair of beavers (Castor fiber) 

created a series of 13 dams on a straightened, channelized, and hydrologically isolated stream. 

Pond creation increased the surface water storage capacity by an estimated 1000 m3. In 

addition, the beaver activity significantly altered surface flow regimes; comparisons of data 

collected over a 15 month period both upstream and downstream of the beaver effected area 
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showed an average reduction in peak flows of 30%, an increase in peak rainfall to peak flow 

lag times of 29%, with 22% more water entering the beaver modified area than exiting the site. 

The greater retention of water on-site may result from increases in evaporation, 

evapotranspiration, transmission, or infiltration into the subsurface. 

Sediment, nutrients, and contaminants -- Sediment includes mineral and organic 

particulate matter that moves downstream via river transport. The ability of flow to carry 

sediment largely depends on velocity, so slower currents associated with beaver ponds and 

overbank flows allow sediment to be deposited, which reduces the suspended sediment in the 

river water and helps create and maintain fertile floodplain soils. Although suspended 

sediment is an integral component of stream systems and a normal feature of flood waters, it 

is also considered one of the most widespread “pollutants” in the United States (Waters, 1995). 

This is largely because human activities such as construction and agriculture have 

dramatically increased the amount of fine sediment entering rivers while concurrently 

reducing floodplain connectivity where fine sediments would naturally deposit (Hooke, 2000). 

High concentrations of suspended sediment reduces photosynthesis for aquatic plants and, at 

very high concentrations, can clog the gills of fish and salamanders, and abrade bottomdwelling stream insects (Van Nieuwenhuyse & LaPerriere, 1986; Reynolds et al., 1989; Chiu et 

al., 2013). When excess fine sediment is deposited on the streambed, it can smother spawning 

gravels for fish, as well as bottom-dwelling organisms (Wagener and LaPerriere, 1985; Ryan, 

1991). Fine sediment can also block municipal water intakes, reducing the efficiency of these 

structures. Where suspended sediment enters water intakes, it must be physically removed 

from the water through filtering. At the same time, fluvially-derived fine sediment is an 

essential component of floodplains and forms the basis for the rich farmland soils found on 

most valley floors. It also helps to structure the beds of rivers, provides stability to banks, and 

creates microsites for the establishment of riparian plants (Cluer & Thorne 2014). Thus, where 

suspended sediment is considered a pollutant, there is an opportunity to turn it into a resource 

through careful management and reconnection of floodplain systems.

Many compounds adsorb, or physically attach, to silt and clay particles. Compounds such as

nutrients and organic matter are necessary to living organisms but can be detrimental in high 

concentrations, such as nitrogen and phosphorus. High concentrations of nitrogen and 

phosphorus can create numerous negative effects, including eutrophication and hazards to 

human health. Eutrophication occurs when populations of blue-green algae increase 

dramatically in response to excess nutrients. When the algae die, the processes by which they 

decay reduces dissolved oxygen concentrations in the water, which can kill invertebrates and 

fish. When drinking water with excess nitrogen is consumed by humans, it can result in bluebaby syndrome, a potentially fatal condition associated with low oxygen levels in the blood 

and, over longer periods of ingestion, can result in non-Hodgkin’s lymphoma, the most 

prevalent form of cancer in the United States (U.S. Geological Survey, 1999; Nolan and Stoner, 

2000). Excess nitrogen in groundwater is of particular concern in farming communities. For 

example, researchers found that nearly 10 percent of the 2.6 million people living in the Tulare 

Lake Basin and Salinas Valley in California might be drinking nitrate-contaminated water 

(Holbrook, 2012). Organic carbon also commonly moves with fine sediment. Although 

dissolved organic carbon is not harmful to humans, it can create unpleasant tastes and odors 

in drinking water, so that the water is typically treated with chlorine. However, chlorine reacts 

with dissolved organic carbon to produce disinfection by-products known as trihalomethanes, 
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which are known carcinogens (Steingraber, 1998). Hence, expansion of beaver populations in 

urban areas where there is an opportunity for floodplain reconnection, may provide a ‘sink’ 

for nutrient-rich sediments. 

Extremely toxic materials also physically attach to silt and clay particles. Mercury, heavy 

metals including zinc, cadmium, lead, and a variety of synthetic compounds including PCBs, 

DDT residues, other pesticides, and volatile organic compounds, such as additives in gasoline 

and varnishes, all move with fine sediment (Wohl, 2015a). All of these materials, which are 

teratogens (cause developmental changes and abnormalities), mutagens (cause chromosomal 

changes), and carcinogens (cause cancer), are commonly detected in runoff from urban areas 

(Lopes and Bender, 1998; Nowell et al., 1999; Rice, 1999; Squillace et al., 1999; Nowell, 2001). 

Where sediment deposition is focused within a specific river segment such as a beaver 

meadow, downstream dispersal of toxic materials can be reduced. Deposition of fine sediment 

in beaver meadows thus has a variety of secondary benefits in the form of improved water 

quality as a result of removing sediment, nitrogen, phosphorus, and carbon, as well as a 

variety of toxic contaminants, from downstream water, which is especially important in urban 

areas where water quality is often degraded (Correll et al., 2000; Wohl, 2013; Johnston, 2014;

Lazar et al., 2015).

While there is very limited research on the long-term effects of toxic material accumulation in 

urban beaver ponds, there has been extensive research on urban bioretention systems and rain 

gardens. For example, Hong et al. (2006) found that approximately 90% of naphthalene, 

toluene, oil, and particulate-associated naphthalene was biodegraded within approximately 8

days following accumulation. This approximation was based on reduced contaminant 

concentrations combined with increased microbial populations. Until there is additional 

research on urban beaver ponds, the stormwater and bioretention literature provides a 

reasonable surrogate for risk analysis.

Education and Outreach Benefits

Because beaver are becoming increasingly common in suburban areas, they are being 

incorporated as learning and teaching tools for both children and adults (see Martinez, 

California example in Chapter 11: Beaver Restoration Case Studies). As a charismatic species 

(Muller-Swarze, 2011; Wolff & Sherman, 2008), beaver play a distinctive role in engaging the

public with the natural environment and also demonstrating species interdependence. Urban 

beaver provide first-hand lessons about habitat, biodiversity, territory and trophic cascades. 

Children can see with their own eyes how the population of birds, frogs, turtles and other 

wildlife respond to construction of a beaver dam. On field trips to a beaver dam, they can 

become mini-detectives looking for tracks, chew marks or scat. They can even observe the 

distinguishing characteristics between otter, beaver and muskrat. Since urban beaver have 

been known to habituate to traffic, crowds, and city noises, they are often less difficult to 

directly observe, which further engages the public (see Martinez, California case study).

Even when beaver are not visible, their dams, lodges and characteristic chewing leave telltale 

clues about nocturnal activities – inviting greater curiosity. Teachers can easily incorporate 

these lessons into curricula for any age, teaching younger children about habitat and survival, 

and older children about overlapping biodiversity or ecosystem services. An example is a 
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middle school unit of study termed “A Look at the Industrious Beaver: Nature’s Engineers” 

(http://evavarga.net/2016/07/10/beaver-natures-engineers/).

Other examples include school a curriculum development in Stafford, Connecticut, which 

taught beaver ecology through water sampling and observing forest biodiversity at a nearby 

beaver dam, the beaver biodiversity project by Teens4Oceans.org, and the northern California 

town of Martinez, which celebrates its urban beaver population every year with an annual 

festival (see the Martinez, California, case study). 

More than a hundred years ago, Enos Mills (1913) described the learning opportunities for

children, noting:

Beaver work may do for children what schools, sermons, companions and even home sometimes 

fail to do, - develop the power to think. No boy or girl can become intimately acquainted with 

the ways and works of these primitive folk without having the eyes of observation opened, and 

acquiring a permanent interest in the wide world in which we live.

(Enos Mills, 1913, In Beaver World)

Social Benefits

Numerous studies have shown the psychological and physical benefits of urban wildlife to 

local residents (Maller et al., 2006; Tzoulas et al., 2007; McClutcheon, 2016). They include stress

reduction, greater feelings of well-being, increased community cohesion, and even crime 

reduction (Weinstein et al., 2015). Some researchers argue that wildlife’s significance in urban 

planning should be regarded with as much weight in composing a healthy community as 

open space or air quality (Bjerke & Østdahl, 2004). Surprisingly, this appears to hold true even 

when public opinion recognizes that wildlife can cause unwanted or destructive effects 

(Dandy et al., 2011). People consistently report feeling enriched by living with nature. 

Beaver Challenges in Urban Settings

When beaver and humans come into contact, whether in an urban, rural, or wildland context, 

there are challenges of “cohabitation” including flooding, chewing of vegetation, and digging. 

In urban settings, the negative effects from beaver modifications are often amplified due the 

proximity of heavily modified public and private infrastructure. Urban waterways provide 

ample opportunities for beaver damage including flooded roads, property, trails or ball fields,

catastrophic floods due to dam failures, denning in manholes, blocking culverts, plugging 

storm drains, and chewing landscaping. Cities commonly report that beaver damage costs

tens to hundreds of thousands of dollars to repair. Hence, it is understandable that cities may 

resort to trapping as their only perceived cost-saving solution. 

Flooding 

Beaver dam induced flooding in an urban setting typically results from partial or channel 

spanning dams, which create an upstream pond, or force flows laterally onto adjacent 

surfaces. Because urban streams are often artificially narrowed channels and constrained 
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waterways, beaver dams can quickly cause bank overtopping, leading to inundated trees, 

property, public roadways and trails. Additionally, an increased density of roadways, 

railways, and other infrastructure result in numerous culverts and bridges to maintain flow. 

Culverts can be particularly problematic because they vary in size and shape (e.g. round, 

square, pipe arch), which make some more susceptible than others to plugging by beaver 

(Jensen and Curtis 1999). A plugged culvert can cause roadways to rapidly overtop, leading to 

washouts. Cities often counter with heavy equipment to clear and remove obstructions. 

When beavers plug culverts or impound water behind dams, there is often a resultant rise in 

the local water table. There are also fears that adjacent roadways may be susceptible to

damage not only from overland flows, but also from the continual saturation of the roadbed

where this was not considered in the road design and construction (see Portugal et al., 2015). 

With increased and prolonged saturation, the thinking is that the underlying road substrate 

may become plastic, or even fluid, compromising the structural integrity of the roadway (see 

Portugal et al., 2015; Gerich, 2004). Callahan (2003) reports that in the northeast US a 

significant majority of beaver complaints concern blocked culverts and state that “for a 

relatively small amount of work, beaver can create a large pond by plugging a culvert.” Indeed, 

beaver seem drawn to undersized culverts because they provide an excellent opportunity to 

create a dam with minimal effort. In areas where beaver repeatedly plug culverts, it is 

advisable to evaluate the culvert capacity to determine if it is undersized.

Chewing

While localized flooding and blocking of culverts can cause damage, an analysis of 

depredation permits for California from 2013 -- 2014 showed that the most commonly 

reported problem was not flooding, but rather chewing (see www.martinezbeavers.org for 

more information). Around 36% of depredation permits issued were for damage to crops, 

trees, landscaping, or vineyards. Newly planted vegetation at mitigation and other restoration 

sites offer beaver an easily accessible and desirable food resource. This may be especially true 

in urban habitats where there is a lack of riparian vegetation or ‘open-spaces’. In highly 

altered systems with little riparian vegetation, beaver herbivory has the potential to interfere 

with meeting initial riparian vegetation cover requirements necessary to receive mitigation 

credits (See section 404(b)(1) of the Clean Water Act). The saplings planted in abundance at 

many restoration and mitigation sites are an attractive size for beaver chewing, especially in 

areas where there is no other preferred vegetation (see Aldous, 1938). Until the native riparian 

vegetation has had time to mature, it may be at higher risk of mortality from herbivory by 

beaver and management actions to protect the site for the first few years may be necessary.

Urban Beaver Management Strategies

Beaver management plans help guide efforts on many levels, from statewide guidelines, to 

environmental groups, to jurisdictional agency plans (ODFW, 2009; OLSD, 2014, APNM, 

2010). However, site-specific goals, strategies, and objectives necessarily vary to reflect the 

unique characteristics of each site. Goals for each site will vary depending on stakeholder 

needs and concerns and site characteristics, which is particularly challenging in urban settings. 

Thoroughly evaluating appropriate options for the site, including tolerance to beaver 
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presence, beaver exclusion from selected plants or areas, infrastructure protection, pond 

leveling, beaver removal, or some combination of these strategies, along with a clear 

evaluation of the consequences and benefits of each option, requires time and patient 

involvement of all interested parties. A more detailed account of the planning and 

implementation framework around identifying goals, developing strategies and objectives, 

and choosing tactics for beaver restoration/mitigation efforts can be found in Chapter 4,

Section: Goals, Strategies, and Objectives. Regardless of the beaver-related issue, 

understanding the social dynamics and perceptions of beaver activity is an essential step to 

developing an appropriate management plan (Hood, 2015); this aspect is important in all 

beaver projects, but especially emphasized in urban scenarios where human–beaver 

interactions are more probable.

Human dimensions of urban beaver management

In places where both human and beaver population densities are high, human-wildlife 

conflicts increase (Siemer et al., 2013). Addressing the physical issues created by the conflict is 

an essential part of the solution, but public perceptions about the conflict and the cultural, 

social, economic, and political aspects must also be addressed and incorporated into 

management decisions (Madden, 2004). Comprehensive understanding of local perceptions 

regarding beaver and beaver management is necessary to identify key points of contention 

and to aid in solution development (Goedeke & Herda-Rapp, 2005). The local perception of 

beaver presence is paramount in urban beaver alternative analysis. 

Due to the greater number of stakeholders in urban areas, additional effort is required to 

ensure that concerns are understood and addressed when developing management objectives. 

The contrasted scenarios in our case studies in Martinez, California and Tualatin, Oregon

demonstrate how beavers can elicit different responses from public agencies, private citizens, 

and community groups over similar issues, and how pathways to success also vary. In 

Martinez, citizen groups lobbied the city to adopt a “living with beaver” approach in response 

to beaver colonization in the city center; whereas in Tualatin, the water resource management 

agency and parks department have been promoting acceptance of beaver in their Greenway 

Park.

As with rural and wildland beaver restoration projects (see Chapter 4: Watershed Planning for 

Beaver Restoration Projects), convening all interested stakeholders early in the process is 

essential. Regardless if it is one small site, or a city-wide, non-lethal beaver management effort, 

managing expectations of landowners and land managers helps to achieve both the broader 

project goals (e.g. maintain viable dispersing populations of dam-building beaver colonies) 

and more measurable project objectives (e.g. floodplain reconnection). 

In Oregon, Needham & Marzillo (2011) found that most private landowners in the state did 

not think lethal removal of beaver from the landscape was an acceptable management 

technique. However, both non-structural (e.g. informational pamphlets on how to coexist with 

beaver, expert home visits) and structural management (e.g. fencing, flow control devices) to 

help mitigate the negative impacts from beaver colonization were considered appropriate. The 

authors also found that landowners who had previously experienced negative impacts from 
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beaver were less likely to use non-lethal management techniques. Early stakeholder

engagement can help to avoid future conflicts. 

Evolution of Current Management Strategies 

The history and efficacy of past beaver management strategies is an essential step in 

developing and implementing successful management plans (Taylor 2009). Historically, lethal 

trapping was a common means to manage disruptive beaver activity, and is still considered a 

valid tool; however, effective, non-lethal tools have become increasingly preferred by the 

public (Needham & Marzillo, 2011; Taylor 2014). As the ecological contributions of beaver to 

their environment is more fully understood, many management plans have evolved 

accordingly. 

Growing global urbanization has increased the demand for ecosystem services to help off-set

environmental impacts (Elmqvist et al., 2015). Ecosystem services provided by beavers 

through their dam building activities is increasingly recognized by land managers (Hood 

2011). As a result, mitigating the negative impacts of beavers in order to allow continuation of

these services is gaining traction, and beaver management plans are beginning to reflect this 

trajectory (Oregon Dept. of Fish and Wildlife & Washington Dept. of Fish and Wildlife

Guidance on Beavers; Oak Lodge Sanitary District “Living with the American Beaver,” 2014;

Wisconsin State Beaver Management Plan, 2015; Utah State Beaver Management Plan;

Pennsylvania State Beaver Management Plan; Nevada State Beaver Management Plan; City of 

Portland (Multnomah County Drainage District Beaver Management Plan, (still in 

developement)).

Adaptive Management

Beavers in the urban environment are usually managed in response to infrastructure or 

private property impacts (Baker & Hill, 2003; Lacitis, 2009; Sullivan, 2012). As beaver 

management shifts towards non-lethal mitigation techniques, more emphasis is placed on 

developing adaptive management strategies to satisfy multi-stakeholder concerns. Successful 

plans are cooperative in nature and integrate public communication as a key aspect of the 

science-based decision-making process (Hood, 2015). In adaptive management, stakeholder 

concerns and objectives are identified, management alternatives and predictive models are 

outlined, and a baseline monitoring framework is established that adequately characterizes 

initial concerns (Williams, 2012). Thresholds are then set that trigger management responses 

and adjustments if exceeded (Nie & Schultz, 2011); this allows practitioners to monitor project 

outcomes and thus ensure that concerns are being addressed through time (Portugal et al.,

2015). Stakeholder concerns and thresholds vary widely depending on a host of factors 

including, but not limited to, regional ecology, regulatory guidelines, and land use objectives. 

The adaptive decision-making process provides a reliable and effective approach to urban 

beaver management that can be applied across a wide variety of scenarios. The United States 

Department of the Interior released an Applications Guide to Adaptive Management in 2012; 

the report provides extensive detail into development of strategies.
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At least four states have active statewide beaver management plans (Nevada, Wisconsin, 

Pennsylvania, and Utah) along with a citywide adaptive beaver management plan (Park City, 

Utah) (Wheaton, 2013). The goal of the Park City plan was to balance both the ecological needs 

of beaver and benefits to Park City residents, while protecting public and private property and 

resources. To achieve this balance, first the Beaver Restoration Assessment Tool (McFarlane et 

al. 2014, 2017) was applied to the drainage network of Park City to estimate where beaver 

were likely to build dams. Assessments of existing or past beaver occupation, and the 

classification of the different river segments located within the city limits, was then carried 

out. Finally, an adaptive management plan was developed and initiated to assess beaver 

activity at various scales (city wide, classified reaches, and individual beaver dams) so the 

appropriate management techniques could be applied to achieve the overall goal (Wheaton 

2013). 

Scale Considerations

The adaptive management strategies outlined above are not scale-dependent. Managers are

often constrained by jurisdictional boundaries and thus need only commit resources to 

analysis and monitoring within their boundaries. However, individual beavers or colonies are 

one part of a larger, landscape level population of beavers that transcend jurisdictions. Beaver 

are mobile and can travel long distances (Windels, 2014). Assessing and evaluating 

management strategies over the broadest area possible will provide a description of potential 

conflicts where beavers might disperse. 

Non-lethal management of beaver at the reach scale, or at a specific restoration or conservation 

site, will follow the same strategies underpinned by the adaptive management process. One 

advantage of managing beaver at smaller scales (i.e. city-wide, or smaller sites within a city), is 

the ability to assess and make management decisions at every individual beaver dam 

(abandoned and active) or area of concern (e.g. culvert) within the project area. For example, 

beaver may be damming a reach of stream with adjacent sensitive infrastructure. Instead of 

immediately removing the dam, managers can assess the effect of the dam and make decisions 

based on pre-established thresholds (see Wheaton 2013). Dam presence does not necessarily 

equate with negative impacts. If the dam increases in size, or more dams are added to the site,

a management action may be triggered and future management decisions can be made. For an 

example of applying the adaptive management process at a small urban wetland site, see 

Portugal et al. 2015.

Issues and Treatments

In most cases, effective strategies include a combination of different management techniques, 

prioritized by their ability to meet stakeholder needs. 

Vegetation Chewing Solutions -- Current techniques used to protect vegetation from 

beaver herbivory in rural and wildland settings are also effective in urban areas. Vegetation 

protection in urban areas can actually be easier than in rural areas because of the increased 

number of landowners on relatively smaller parcels of property. Wrapping either individual 

or groups of trees in wire mesh cages can protect important vegetation from beaver damage. 

Mixing outdoor paints with sand and applying the gritty mixture to trees can also deter 
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beaver from chewing. See Chapter 9: Non-lethal Options for Mitigating the Unwanted Effects of 

Beaver for more details. 

We found only one publication on herbivory by urban North American beaver. Loeb et al. 

(2013) investigated whether trails located in Radnor Lake State Natural Area, Nashville, 

Tennessee, act as barriers to vegetation from beaver herbivory. The authors found that raised 

wood board pathways running parallel to the stream that were frequently used by humans 

seemed to significantly reduced uphill vegetation damage from beaver compared to shore

forests located downhill of the pathways. The authors speculate that the human odor from 

traffic on the pathways may have deterred beaver from accessing the vegetation on the uphill 

side of the trails. Other research confirms that predator scent, including humans and bears, 

have shown to impact beaver behavior (Engelhart & Müller-Schwarze, 1995; Rosell & Czech, 

2000; Severud et al., 2011).

Flooding Solutions -- Current techniques used to protect property and infrastructure from 

beaver dam related flooding in rural and wildland settings are appropriate in urban areas as 

well. The installation of flexible pond levelers will prevent the water elevation in beaver ponds 

from rising above a pre-established height, providing a solution to the flooding of 

infrastructure or property, while allowing the ecologically important beavers, their dam, and 

their pond to remain in place. See Chapter 9: Non-lethal Options for Mitigating the Unwanted 

Effects of Beaver for more details. 

Flooding can occur with both active and abandoned beaver dams. Possible solutions to reduce 

the risk of flooding due to abandoned dams located in urban streams is notching or dam 

reinforcement with posts. After beaver colonies have depleted food and construction 

resources, they will abandon a site and disperse to find new territory. However, the presence 

of a pond and slow water habitat, increased stream complexity, and raised local water table

can be beneficial in urban settings. Notching the dam is an effective solution to maintain water 

levels of the pond below identified threshold elevations. With the resident beavers gone, the 

notch or gap in the dam is less likely to be repaired. Reinforcing the dam with vertical posts 

may be the preferred option, especially if there is a desire to store the maximum amount of 

sediment and water; however, maintenance may be required over time if beaver do not 

reoccupy the site. Eventually, the dam may need to be completely reconstructed using a 

Beaver Dam Analogue approach.

In actively maintained dams, beaver will be cued to the sound of flowing water at a notch and 

will likely repair the notched section, often over a single night (Muller-Shwarze, 2011). If the 

installation of a pond-leveler is not possible, a little-known technique called “flagging” may

deter repair of a notched dam. Flagging involves the placement of white strips of flagging 

above a notch in a dam and presumably creates a visual, auditory, and tactile deterrent to 

beaver dam-building and repairs. The effectiveness of this technique is not well-quantified, 

though anecdotal evidence suggests it has worked in certain instances (Portugal et al., 2015). 

We encourage the readers to experiment with this unproven, but low-cost technique and to 

report back the results. 
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Culvert Solutions -- Techniques used to protect property and infrastructure from flooding 

associated with beaver plugging culverts in rural and wildland settings readily transfers to 

urban areas. Culverts can be protected from beaver through installing culvert protective 

fencing. In addition, flexible pond levelers can be used in combination with culvert fencing to 

allow some ponding upstream of the culvert. See Chapter 9: Non-lethal Options for Mitigating 

the Unwanted Effects of Beaver for more details. 

Knowledge Gaps for Urban Beaver

Given the broad literature base regarding beaver and beaver-prompted restoration and 

management, there are still many unaddressed topics. If you are aware of any formal or 

informal research and/or assessment of the following topics, please contact the editors so that 

we may include the information in future revisions. 

Digging -- Digging is a significant concern regarding beavers in cities and elsewhere such as 

agricultural areas. Beavers have the potential to burrow into stream banks or levees to create 

bank burrows, as well as dig out canals to expand their foraging area. In California, for 

example, approximately 15% of depredation permits are issued because of concerns that 

beavers will tunnel into banks or levees (see www.martinezbeavers.org for more information). 

According to the California Department of Water Resources, Urban Levee Design Criteria 

(2012) the structural integrity of levees may be reduced by burrowing animals, while no 

effective method to completely exclude burrowing animals from grass covered levees exists. 

Digging by beaver may also decrease stream bank stability and increase turbidity of urban 

waterways. We found no literature discussing problems associated with beaver digging (canal 

building, burrowing and tunneling) in urban areas or solutions related to such problems. As 

this is an area that needs to be addressed, please contact the editors if you have encountered 

any non-lethal solutions to mitigate beaver digging.

Riparian Buffer Zones -- Although we know that beaver dam-pond pairs and beaver 

meadows can alter the distribution of water in a river corridor through time, substantially 

improve water quality, and enhance habitat and biodiversity, the single largest knowledge 

gap involves the scale of these effects and potential thresholds. The creation and restoration of 

riparian buffer zones that promote biological uptake and sediment storage of nitrogen and 

phosphorus, for example, is increasingly emphasized in urban river restoration. Restoring 

riparian buffers along limited river segments is often not sufficient to remove the enormously 

increased quantities of nitrogen coming from urban lands (Bernhardt and Palmer, 2011), but it 

remains unknown how to scale the length, width, and uptake capacity of riparian buffers – or 

beaver meadows – to create a desired level of nitrogen retention. Most studies of how beaver 

dams and ponds affect downstream fluxes of water, sediment, and nutrients have focused on 

single dam-pond pairs, rather than on the extensive complex of a beaver meadow. 

Consequently, it remains unknown whether five beaver ponds widely spaced downstream, to 

use a hypothetical example, are equivalent to a single beaver meadow that includes five ponds 

in a more restricted length of river. These uncertainties are particularly important in urban 

settings, where space for beaver restoration and protection is limited. 
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Large Wood or Beaver Dams -- Many of the abiotic and biotic benefits described earlier in 

this chapter in connection with beaver dams can also occur as a result of channel spanning 

large wood accumulations. Benefits resulting from large, persistent wood jams include 

attenuation of peak flows, creation of secondary channels, storage of fine sediment, enhanced 

hyporheic exchange, greater habitat abundance and diversity, and biodiversity (Hester &

Doyle, 2008; Sawyer et al., 2011; Wohl, 2011; Collins et al., 2012; Beckman & Wohl, 2014). Large 

wood jams and beaver dams are members along a continuum of storage of large wood in 

channels (Wohl, 2013, 2015). Few studies have considered large wood and beaver dams 

comparisons, and we do not currently have guidelines for the conditions under which urban 

river restoration might most effectively target engineered (Abbe et al., 2011; Gallisdorfer et al., 

2014) or naturally occurring wood (Wohl et al., 2016) versus beaver dams as mechanisms to 

improve water quality and habitat. There are likely to be distinct benefits and hazards 

associated with each type of obstruction on urban rivers, but these have not yet been 

systematically characterized or compared between different types of obstructions.

Contaminants -- Beaver ponds can act as long-term sinks for contaminants such as nitrogen 

(Lazar et al. 2015), and retain other contaminants that attach to fine sediments deposited 

behind beaver dams. Reducing the flux of these contaminants downstream is a common goal 

of river restoration projects. However, contaminants retained in beaver ponds can become 

mobile after beavers abandon the site or dams are breached or washed out. Perhaps removal 

of contaminants stored behind beaver dams can further reduce future negative downstream 

effects. This could be accomplished through dredging of contaminated pond sediments, 

removal of emergent vegetation after the up-take of contaminants into the plant biomass, or 

the installation of floating wetland treatments to expedite the up-take of contaminants out of 

the water column. More research is needed to ensure that anthropogenic removal of 

contaminants out of beaver ponds is effective and not detrimental to the resident beavers or 

the associated plant and wildlife. 

Management Plans -- To create robust and effective urban beaver management plans for the 

diverse range of urban settings in North America, more research is needed regarding the 

overall effects beaver have in urban waterways. The United States Geological Survey (USGS) 

and Clean Water Services (CWS), a water resource management utility located in Portland, 

Oregon, is implementing a basin-wide research study on the effects of beaver dams and ponds 

on urban streams in the Tualatin River Basin. The study seeks to answer the following 

questions:

1. What is the current distribution of beaver dams in urban streams of the Tualatin River 

Basin?

2. How does the distribution of beaver dams in urban streams relate to landscape variables, 

streamflow, and other variables? Are there threats to local infrastructure, such as 

municipal water intakes, or to flooding of private or public property?

3. To what extent does the presence of a beaver dam increase water stage and depth, 

inundation area, and residence time upstream of the dam? What is the timing, duration, 

and magnitude of water movement through beaver dams to downstream reaches 

throughout the year, during storms in winter, as well as during spring recession and 

summer low flows?
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4. Does the presence of a beaver dam increase the elevation of the nearby groundwater table? 

Does the direction of groundwater flow change direction because of the beaver dam?

5. How does beaver activity affect stream temperature and other water quality conditions?

6. What is the instream geomorphic succession/elevation of an urban beaver dam?

7. How do beaver ponds affect aquatic and terrestrial biodiversity in nearby areas? Are 

certain species or ecological metrics significantly affected by beaver ponds in urban 

streams?

8. What is the succession of vegetation in and around urban beaver ponds?

9. Does large wood in the beaver dams create novel habitat for macroinvertebrates in an 

otherwise flashy urban stream with limited riffle habitats?

The study was initiated in October, 2015, and is expected to be completed by September, 2018. 

Regional differences in the effects from beaver dams on urban streams may exist. Similar 

studies performed throughout the range of the North American beaver will improve our 

understanding of their impacts on urban environments, facilitate non-lethal management, and 

contribute to our knowledge of how to incorporate beaver into urban restoration projects.

Conclusions 

Beaver and human populations continue to expand. In response, it is not unreasonable to 

expect that the waterways, creeks, ponds and ditches close to dense human habitation will 

eventually be colonized by beaver. The reflexive response to the arrival of beaver in our cities 

and towns has often been removal with little consideration for the wide variety of alternatives. 

When beavers are discovered in an urban setting, a more complete, objective consideration of

the full range of alternatives, including beaver retention, with all the possible positive benefits 

that might be gained, should be undertaken. This is not simply out of desire to increase the 

population and distribution of beaver, but it is in recognition of the vast and complex societal 

benefits provided by beaver in urban settings have not been fully valued.
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Chapter 8—Managing Habitat for Beaver

Michael M. Pollock and Gregory Lewallen

Habitat that is intrinsically suitable for beaver may not contain beaver because of active land 

management that selects for other values. Where desired, land management strategies can be 

shifted to encourage beaver colonization. There are three components to management 

strategies intended to support beaver: reducing competition from other herbivores for beaver 

food resources, increasing the abundance of beaver food resources, and reducing beaver 

predation rates, especially from humans.

Reducing Herbivore Competition

In the western United States, elk and deer are the native animals that most frequently compete 

with beaver for food resources, while cows are the most common non-native competitor for 

food. A growing literature exists on methods for keeping cows away from stream corridors so 

that riparian vegetation can recover, primarily through alternative grazing regimes (e.g., restrotation) and riparian fencing (see Figure 33). Competition from elk can also be reduced with 

robust riparian fencing, or the construction of exclosures. Starkey Experimental Forest and 

Range near La Grande, Oregon is running a long-term experiment to assess the effects of 

different grazing and fencing strategies on grazing by elk, deer, and cattle in riparian areas. 

Research in Yellowstone National Park suggests that riparian grazing pressures from elk can 

be reduced by increasing the abundance of elk predators, specifically wolves. In the presence 

of wolves, elk change their behavior, spending less time resting and grazing in riparian areas 

and more time on the move, so that their location is less predictable to wolves. There has been 

a related increase in the abundance of both woody riparian vegetation and beaver. Because 

wolves also prey on beaver it might seem counterintuitive that introducing such a predator 

would increase the beaver population, but this in fact appears to be the case.

Increasing Beaver Food Sources

Areas that lack woody riparian vegetation can be improved by planting easy-to-grow species 

that are preferred by beaver, such as willow and cottonwood. Such species can be propagated 

from planted stakes. A reliable water supply is needed for successful propagation. If beaver 

are already present, it is necessary to protect the newly planted stakes to avoid premature 

harvest. It also can be helpful to estimate the extent of flooding that is likely to be caused by 

beaver dams, so that vegetation can be planted in areas that are not likely to be immediately 

flooded. For more on methods for successfully propagating (and protecting) willow and 

cottonwood, see Hall et al. (2014).
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Reducing Beaver Predation Rates

Humans are beavers’ primary predators, but black bears, coyotes, mountain lions, grizzly 

bears, and wolves can also affect beaver populations. Trapping restrictions are the most

effective means of reducing human-induced beaver mortality. State fish and wildlife agencies 

have administrative procedures for responding to requests that areas be closed to trapping. 

Working with such agencies may be the best avenue for reducing trapping-related beaver 

mortality in specific areas, such as where beaver restoration efforts are taking place, but the 

declining value of beaver pelts has been more effective in reducing trapping-related beaver 

mortality rates. At the Federal level, land agencies such as the U.S. Forest Service and Bureau 

of Land Management adopt land management policies that include beaver management, and 

these policies often provide more protection for beaver than do policies at the state level. For 

example, the Malheur National Forest in Oregon has an ongoing commitment to integrate 

beaver into its aquatic restoration management strategies and seeks to expand beaver 

populations where possible (Malheur-National-Forest 2007).

Figure 33: Recovery sequence of an incised stream 

ecosystem over a 20-year period. In 1993, (a) the stream 

was open to annual summer grazing by cattle. After 1999, 

(b) grazing was limited to cow–calf pairs during spring 

and fall. By 2012, (c) beaver had established a persistent 

colony for several years. The size of riparian vegetation 

had substantially increased, and vegetation now extended 

across the entire width of the incision trench, because 

beaver dams had elevated the water table. Upstream of 

the dams, the channel is (for now) wide and deep. Dams 

and the density of riparian vegetation further increase 

flow resistance and reduce stream power, creating 

conditions ideal for the retention of sediment, but the 

trench width will make aggradation rates low. 

(Photographs: Carol Evans, Bureau of Land Management, 

from Pollock et al., 2014).
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Chapter 9—Non-lethal Options for Mitigating 

the Unwanted Effects of Beaver 

Michael M. Pollock and Gregory Lewallen

Beaver activities that conflict with human interests generally fall into two categories:—tree 

cutting and dam building—and potentially problematic dams can be further divided into 

dams that block culverts or irrigation canals and dams that do not. Historically, in many states

and provinces throughout North America, lethal removal of beaver has been the method of 

choice for solving such beaver/human conflicts, but more interest in non-lethal approaches

has been growing. 

Non-lethal approaches have gained popularity for a number or reasons, including the 

following:

 Non-lethal management is more effective and less costly than lethal removal (Callahan 

2005, Simon 2006, Boyles and Savitzky 2008).

 The public is becoming increasingly dissatisfied with lethal removal, in part because of 

concerns that trapping and drowning or bludgeoning beaver is not humane (IAFWA 

1997, AVMA 2000, Hadidian 2003).

 There is growing demand for live beaver, because of organizations’ and agencies’ 

renewed interest in re-introducing beaver to locations where they can provide 

environmental benefits (Apple 1985, Boyle and Owens 2007, Pollock 2012) (Olsen and 

Hubert 1994, McKinstry et al. 2001). 

Non-lethal approaches to solving the major sources of human-beaver conflict are summarized 

below.

Tree Cutting

Beaver can travel up to 328 feet (100 meters) from a water body to cut and harvest trees, but 

the probability of harvest decreases exponentially with distance from water (Rutherford 1955, 

Allen 1983, Gallant et al. 2004). Although beaver generally prefer species in the genera Populus

or Salix (cottonwood, aspen, and willow), they will harvest a wide range of trees and shrubs 

(reviewed in Boyle and Olsen 2007 and Baker and Hill 2003). Beaver also use the base of large 

trees of both palatable and unpalatable species as gnawing stations; gnawing can lead to the 

tree’s ultimate demise. As in all burrowing rodents, beaver teeth grow continuously and thus 

need to be continually worn down, which is done primarily by gnawing on wood. 
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Solution: Wire Mesh Cages

There is little in the way of peer-reviewed literature on non-lethal methods for preventing

beaver from cutting trees, but an extensive review of technical information from various 

government and private organization websites suggests that surrounding trees with a 

cylindrical wire mesh cage is the simplest, most effective means of preventing a beaver from 

cutting down a tree (Figure 34) (e.g. beaversolutions.com, APNM.org, beaversww.org, 

martinezbeavers.org, www.kingcounty.gov/environment/animalsAndPlants/beavers). Cage 

specifications vary slightly, but recommendations generally are as follows: 

 Wire mesh gauge should be reasonably heavy (e.g., 6 gauge) to prevent beaver from 

chewing through it. Chicken wire is not recommended.

 Mesh size should be 6 x 6 inches or smaller.

 The cage should be 1 to 2 feet in diameter larger than the tree trunk.

 The cage should extend 3 to 4 feet above the ground or, in colder climates, above the

anticipated snow line. 

 Wire fencing can be used to encircle multiple trees. 

One of this guidebook’s authors (Pollock) has noted the effectiveness of exclosure cages using 

these specifications at various field sites. Not all cages were 100 percent effective. In some 

cases beaver managed to harvest trees inside of exclosures, presumably by climbing the cages. 

Solution: Paint Mixed with Sand

A number of websites and bulletins also suggest that paint mixed with sand is effective, 

although repeated application is required. For example, beaversww.org recommends a 

mixture of 8 ounces (227 grams) of fine sand (30-mil, 70-mil, or masonry sand) mixed with 1

quart (0.94 liter) of oil or latex paint, matched to the color of the tree trunk and painted to 4 

feet above ground. 

Other Approaches

Placement of 3- to 4-foot-high fences between streams and the trees that need protecting has 

also been suggested, presuming that beaver won’t travel long distances on the upland side of 

the fence because they are exposed to predation. Electric fences strung 4 to 6 inches above the 

ground have also been suggested. We could find no data assessing the effectiveness of these 

approaches. 

Techniques such as chemical deterrents were considered to be marginally effective because 

they work only for a few months at most and repeat application is needed. Techniques such as 

noise and flashing lights appear to deter beaver for a few days at most (Nolte et al. 2003, 

Kimball and Perry 2008).
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(a) (b)

c)

(c)

Figure 34a-c: Illustrations of a wire cage for protecting trees against beaver. Note that all three 

examples show caging that is too close to the trunk of the tree, with (c) showing the inevitable result of 

such a miscalculation. 
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Flooding Problems

Solution: Flexible Pond Levelers

Where beaver dams raise water levels enough to cause unwanted flooding, a large-diameter 

flexible pipe inserted horizontally through the dam in combination with a vertical cylindrical 

wire cage to protect the upstream pipe end from being dammed has also proven highly 

effective in permanently lowering water levels behind a beaver dam (Figures 35 and 36). Such 

devices are generically referred to as “flexible pond levelers,” “flex levelers,” “pond levelers,” 

or “water level control devices.” Callahan (2003) examined the effectiveness of 116 flexible 

pond levelers on free-standing dams that were causing conflicts with humans but that were 

not associated with human infrastructure such as culverts. He found that installation of

flexible pond levelers resolved human-beaver conflicts 83 percent of the time.

(c) (d)

Figure 35: Flexible pond levelers with cylindrical wire cages on the upstream pipe end. Clockwise 

from upper left (a) and (b) are examples during the construction phase, while (c) is an example just after 

completion but before dam repair. (b) is a downstream view of a pond leveler after beaver have 

repaired the dam. Photographs from Boyle (2006).
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When the conflict was not resolved, the failure most commonly was attributed to the beaver 

constructing dams downstream of the installation site; this was the case in 75 percent of the 

sites where the conflict was not resolved. The few remaining failures were due to vandalism 

or insufficient pipe capacity. 

Solution: Clemson Leveler

Another popular method of controlling beaver pond levels and preventing culvert plugging is 

known as a “Clemson leveler.” This is a perforated polyvinyl chloride (PVC) pipe whose 

upstream end is wrapped in wire mesh fencing; the pipe is then inserted horizontally through 

the dam (see Figure 37). Reported success rates with the Clemson leveler are only about 50

percent (Nolte et al. 2000). 

Figure 36: Design specifications for a flexible pond leveler that is used to adjust beaver pond water 

levels to an acceptable level when there is unwanted flooding. The design allows some pond habitat

to remain and is passable to adult salmon. Figure adapted from a design provided by Jake Jacobsen, 

Snohomish County, Washington Public Works Department, Jacobsen (2010).
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Figure 37: A Clemson leveler-style device is not fish-friendly. The small mesh size, the pipe 

perforations, an end cap at the upstream end of the pipe, and an elbow on the downstream end are all 

features that make it challenging for fish to move upstream or downstream. Adapted from Wood et al. 

(1994).

Other Approaches

More extreme measures, such as the use of heavy equipment or dynamite to remove problem 

beaver dams have produced mixed results (Dyer and Rowell 1985). Enthusiasm for such 

approaches seems to be on the decline, presumably because of associated environmental 

impacts to fish, wildlife, and water resources.

Culvert Blocking

Solution: Culvert-Protective Fencing

Considerable research has gone into the development of non-lethal solutions to the 

widespread problem of beaver damming culvert inlets and flooding roads. Several studies 

have evaluated a range of options and found a highly cost-effective solution to be heavy-duty 

(i.e., 2- to 6-gauge) cattle panel wire mesh fencing installed in a rectangular or trapezoidal 

configuration upstream of the culvert (see Figure 38) (Jensen et al. 1999, Jensen et al. 2001, 

Callahan 2003, Boyles 2006, Simon 2006, Boyles and Savitzky 2008). 

In Virginia, Boyles (2006) compared the cost of installing and maintaining fencing upstream of 

culverts with the cost of removing beaver and conducting associated road maintenance and 

repairs. Boyles found that before fencing was installed, the average annual cost for 14 road 
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maintenance sites with beaver activity was $21,500, compared to $3,200 after culvert fencing 

was installed. Callahan (2003) extensively examined the effectiveness of culvert protection 

fences in New England. Out of 131 sites, 126 (96 percent) effectively prevented beaver from 

damming the culverts. Two sites failed because the entire fence was dammed by beaver, two 

others failed because proper maintenance was not performed, and another site was considered 

a failure because a new dam was constructed downstream. Callahan estimated that the 

average cost of the culvert-protective fences was $654, with an expected life span of 10 years 

and an average maintenance time of 1 hour per year for an annualized cost of $190 per year (in 

2003 dollars). Both of these studies included culverts with protective-fences and pond levelers 

because of concerns that the fencing, if partially dammed, would provide insufficient flow 

capacity. 

Similarly, in the Pacific Northwest, some observations suggest that culvert-protective fencing 

alone accumulated enough debris during floods to raise concerns about adult salmon passage, 

although no data were collected (Jake Jacobsen, Snohomish County Public Works, personal 

communication). Therefore, pond levelers were installed at some culverts—in conjunction 

with fencing—to alleviate fish passage concerns. 

Simon (2006) expanded upon Callahan’s study, examining the effectiveness of various beaver 

management strategies at 482 sites. Simon found that culvert-protective fences, some of which 

included pond levelers, were effective 97 percent of the time (at 220 out of 227 sites). Pond 

levelers not associated with roads were successful 87 percent of the time, cylindrical fences 

attached to the inlet of culverts were successful 60 percent of the time, and lethal removal by 

trapping was successful just 16 percent of the time because other beaver quickly occupied the 

site. Simon found the 10-year annualized installation and maintenance costs of culvert fences, 

culvert fences with pond levelers, and pond levelers to be $275, $290, and $200, respectively. 

Figure 38: Examples of culvert-protective fences. From left to right: (a) and (b) are stand-alone 

culvert-protective fences, while (c) is a stand-alone fence combined with a flexible pond leveler pipe 

(underwater and not visible) and a cylindrical wire mesh cage, which provides extra protection against 

obstruction. Figures from Boyle (2006).

Solution: Right-Sizing Culverts

The right-sizing of culverts is another approach that has been advocated to reduce 

beaver/road conflicts. Many culverts are undersized or contain design elements that are 

attractive to beaver. Jensen and Curtis (1999) comprehensively examined factors correlated 

with beaver damming culverts on streams in New York. On streams with a 3 percent gradient 
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or less they found that the frequency of culvert plugging by beaver decreased exponentially as 

the culvert inlet opening increased in size, and that size was the most important predictor of 

culvert plugging (Figure 39). Culverts with an 8.6-square-feet inlet area (i.e., 3.3 feet in

diameter) had a 73 percent chance of being plugged by beaver, whereas culverts with a 113 

square-foot opening (i.e., 12 feet in diameter) had a 7 percent chance of being plugged. 

Figure 39: Relationship between the size of a culvert opening and the probability that beaver will 

plug the culvert, for streams < 3% gradient in New York (adapted from Jensen and Curtis 1999). For 

reference, the areas of the culvert openings for a, b, c and d approximately correspond to circular 

culverts with diameters of 3 ft, 5 ft, 7 ft and 12 ft, respectively.

Jensen and Curtis (1999) also found that pipe arch culverts that maintain the stream width are 

less likely than round culverts to be plugged by beaver. They speculated that round culverts 

are more attractive to beaver in part because they channel water and reduce stream width; 

Jensen and Curtis found that, on average, stream width at plugged culverts was twice the 

width of the culvert inlet opening. Jensen and Curtis thought that round culverts may also 

generate flow noise that attracts beaver but found that the frequency of plugging did not differ 

between smooth-walled and corrugated pipes. They further found that culverts that extended 

beyond the road prism were no more likely to be plugged than culverts that were flush with 

the road prism. Jensen and Curtis also examined the annualized costs of replacing small 

culverts with larger ones and found that annualized costs for various pipe arch and box 

culverts with 10.5-square-meter openings ranged from $881 to $1,717 (1999 dollars), about 
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three to six times the annualized costs estimated by Simon (2006) for culvert-protective fences 

with pond levelers. There are other potential benefits to using large culverts (with natural 

streambed bottoms) that should be considered, including improved passage of fish, wildlife, 

sediment, and organic matter, as well as increased stream habitat.

Fish Passage through Culvert-Protective Fences and Pond 

Levelers

There is little published research on how pond levelers or culvert-protective fences affect fish 

passage. A fence with a small mesh size will impede migrating adult salmon. The only study 

we could find that mentioned mesh size in the context of fish passage was Hall et al. (2005). In 

their study on the Skagit River, Washington, Hall et al. found that numerous chum salmon (O. 

keta) were able to volitionally pass through a flexible horizontal pipe that had a vertical 

cylindrical wire cage with 10 x 15-centimeter meshing attached to the upper end. In 

Snohomish County, just north of Seattle, the Public Works Department built more than 50 

flexible levelers using 10 x 15-centimeter mesh or 15 cm x 20-centimeter mesh, which they 

considered “fish friendly.” Although they did not do a formal study, repeated site visits 

during the fall when adult salmon migrate never revealed a fish blockage problem and 

spawning fish were observed upstream of many sites (Jake Jacobsen, Snohomish County 

Public Works, personal communication). 

The mesh size of Clemson levelers is typically too small to pass adult salmon. Mesh sizes 

ranging from 1 x 2 inches to 2 x 4 iches have been recommended (Wood et al. 1994, Langlois and 

Decker 1997, Brown 2001, MDNR 2001). Typical pipe diameters for Clemson-style levelers are 

7.9 to 9.85 inches, and the levelers may be 20 feet long or longer, which can present an obstacle 

to the upstream movement of large fish such as adult salmon, particularly if the pipe is capped 

as is often suggested (Wood et al. 1994, Langlois and Decker 1997, Brown 2001, MDNR 2001). 

Close (2003) was able to modify a Clemson-style pond leveler on a stream in Minnesota to 

allow passage of 10 brook trout ranging in length from 6 to 8.6 inches, a size still much smaller 

than most adult salmon.

Numerous pond levelers and other devices designed to mitigate human-beaver conflicts are 

described in Gerich (2004). However, many of these devices, such as beaver exclusion fencing 

with perforated pipes, array piping, pond drain pipes, and wire mesh culverts, appear 

impassable to fish. Also included are a number of designs for various fencing and pond leveler 

combinations that appear to be passable to fish.

The movement of both adult and juvenile fish across pond levelers may also be impeded by 

the placement of the downstream end of the pipe. A number of pond leveler diagrams

(particularly for Clemson-type levelers with rigid pipe), have the pipe perched above the 

streambed on the downstream end. This presents a clear passage obstacle for fish. The location 

of flexible leveler pipes can also present problems if the outlet is placed in a riffle rather than a 

pool, or if the outlet is too far downstream of the dam and migrating fish are unable to find the 

opening. Placing the outlet of a flexible leveler in a pool, with the outlet close to the face of the 

dam, minimizes fish passage problems.
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Chapter 10—Beaver Dam Viability Matrix: A 

User’s Guide

Janine Castro

Background

The Beaver Dam Viability Matrix is an outgrowth of the Project Screening Risk Matrix—one of 

several tools generated by the River Restoration Analysis Tool Project (RiverRAT), a broad 

Federal effort to more efficiently and effectively evaluate stream management proposals. For 

additional information on the RiverRAT Project, see

https://www.webapps.nwfsc.noaa.gov/apex/f?p=275:1:.

The purpose of the Beaver Dam Viability Matrix is to assist project managers in quickly 

assessing the likelihood that a beaver dam will persist over at least two seasons—the time 

needed for a mating pair of beaver to successfully rear their offspring. Depending on where a 

project site plots on the matrix, appropriate restoration techniques and tools can be selected or 

an alternative site pursued. 

Explanation of the Axes

The matrix has two axes that transition from the highest dam viability in the lower left corner 

(green), to the lowest viability in the upper right corner (red). Green indicates a higher 

likelihood that a beaver dam will persist naturally or that it will not be removed through 

management actions.

The x-axis represents decreasing beaver dam viability. Decreased viability may be due to

natural conditions, such as those caused by a flood or drought, or human-induced conditions, 

such as channelization or urbanization. The x-axis, therefore, uses attributes such as stream 

slope, valley form, channel incision, the presence of vegetation and beaver, and flow regime to 

assess overall dam viability. Because dam viability is associated with inherent stream 

properties, risk along this axis cannot be reduced unless the project site is relocated or 

significant restoration work, such as levee removal or floodplain reconnection, is undertaken.

The y-axis represents the increasing negative impact potential. This axis uses indicators such 

as project context and scale, land use, infrastructure, and monitoring to assess overall risk if 

the proposed project were implemented (e.g., how likely is it that a dam will be removed).

Reducing risk on the y-axis is often feasible through project redesign, implementation of best 

management practices (BMPs), public outreach and education, and increased monitoring and 

adaptive management.
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Explanation of the Factors

X-axis: Decreasing Beaver Dam Viability

Stream Slope Categories:

<1%

1 - 3%

> 3%

To persist over years, beaver dams must withstand forces (i.e., stream power) from ongoing

flowing water. Because stream power is a product of the density of water, gravity, stream 

discharge, and channel slope, slope is a key element in determining dam viability. Beaver also 

require riparian vegetation for food and building materials, and riparian areas are most 

extensive when there is a floodplain. Floodplains become intermittent to non-existent at 

stream slopes greater than about 4 percent.

Valley Form Categories:

Wide floodplain

Narrow floodplain

Confined channel

Gross valley form controls the habitat potential for beaver because the animal relies on 

riparian vegetation. A channel that is confined by valley walls has low potential for floodplain 

creation or reconnection over time. If a channel is incised into a wide floodplain, there is still 

the potential to reconnect the floodplain. The “valley form” factor evaluates the intrinsic 

geomorphic potential for beaver dam viability.

Channel Incision Categories:

Yearly out-of-bank flow

Occasional out-of-bank flow

No out-of-bank flow

If a channel is connected to its floodplain, water will flow out onto the floodplain in most 

years except in the case of drought. In disconnected floodplains, flooding may only occur only 

every 5 or 10 years, while in extreme conditions, flow may never access the disconnected 

floodplain. Floodplains provide significant energy dissipation, and when they are 

disconnected from the stream all of the energy is concentrated in the channel. For this reason, 

unit stream power is much higher in incised channels than in their unincised counterparts, for 

a given discharge.

Riparian Corridor Categories:

Continuous/wide

Semi-continuous/wide

Discontinuous/narrow

Urbanized or levee confined
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Riparian vegetation provides essential building materials and food supplies for beaver, but 

vegetation also increases the capacity of the stream to absorb disturbances. The probability 

that the stream may be adversely affected increases when the riparian corridor is narrow or 

discontinuous. Riparian vegetation both reduces velocity and increases soil strength. Risk 

increases in urban and levee-confined streams that lack the space necessary to dissipate stream 

energy, and thus beaver dam viability is also reduced.

Beaver Presence Categories:

Established, thriving colony

Evidence of past occupation

No evidence of past occupation 

Determining beaver intrinsic potential is an inexact science. Even with a thorough 

understanding of beaver life history and habitat preferences, it is still challenging to predict 

where beaver will establish a colony. Field indicators of past or present beaver use are 

excellent indicators of potential future use. If there is no indication in the historical or 

geomorphic record of beaver occupation, the likelihood of colonization is very low.

Dominant Hydrologic Regime Categories:

Spring-fed

Snowmelt

Rain

Rain-on-snow

Convective 

Thunderstorm

Flow characteristics are a function of watershed hydrology. Whether the flow is dominated by 

spring-fed or rain-on-snow events profoundly affects the relative channel stability and 

potential for stream response. For example, spring-fed stream systems have low flow 

variability and thus are highly stable and predictable. In contrast, convective thunderstormdriven hydrology results in streams with high variability, so flows in these streams are often 

unstable and unpredictable. The “flashier” the hydrology, the lower the dam viability 

becomes. In higher variability systems, dams in side channels or a cascade of dams may be 

more viable than dams in the main channel.

Y-axis: Increasing Negative Impact Potential

Planning Context and Scale Categories:

Coordinated watershed plan

Stand-alone project

Multi-reach scale

Reach scale

Site scale

All stream management and beaver restoration projects should be developed within a 

watershed framework; this is especially important when identifying the underlying causes of 
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a problem. The “planning context and scale categories” risk factor uses watershed plans as a 

surrogate for project prioritization and context. It is assumed that if the project is identified as 

part of a larger plan that some level of technical analysis has been performed to justify the 

need and appropriateness of the proposed project.

The multi-reach, reach, and site-scale factors acknowledge that beaver will use resources 

within an area until they are depleted and then move to adjacent areas with suitable habitat. If 

a site is too small or isolated, the beaver will not have the space necessary to sustain a colony 

over time.

Adjacent Land Use Categories:

Open space

Agricultural

Rural/suburban

Urban/industrial

Beaver/human conflicts increase when available habitat is limited, there is human 

encroachment on habitat, and the land value in the area is high. Adequate space for beaver, 

combined with land uses that are not vulnerable to increased flooding and saturation, results

in a lower potential for beaver dam removal.

Infrastructure Categories:

None

Bridges

Culverts

Intakes/outlets

Flooding is addressed in the “land use” factor, above. The “infrastructure” factor is specifically 

about water management concerns and the impact of beaver. Bridges are a relatively low risk 

because their openings are large and generally do not result in increased beaver activity; 

however, culverts (especially undersized culverts) attract beavers because of the ease with 

which they can block a culvert entrance and create a pond. This behavior is further 

encouraged because beaver respond to the sound of flowing water, which is amplified when a 

culvert is perched. Beaver ponds can also cause significant problems if there are water intakes 

or outlets, where specific water levels are required.

Monitoring Plan Categories:

Adaptive management

Monitoring only

None

Because all projects have some unanticipated outcomes, monitoring is needed to determine 

the extent of any negative impacts (along with the expected benefits). Although monitoring 

will detect changes and help to identify problems, adaptive management will allow for 

correction of these problems.
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For higher risk projects or new project types, an adaptive management plan can help to 

significantly reduce the overall risk over the long term and improve future projects.

Using the Matrix to Screen Projects 

Once the factors have been assessed, projects risks can be combined and analyzed in at least 

three different ways:

 Assume that all factors are critical to achieve beaver dam viability. In this case, the 

overall risk category is defined by the highest risk factor on each of the x- and y-axes. A 

good example of this precautionary principle is a levee-confined channel, which would 

always receive a high risk rating for low beaver dam viability.

 Consider none of the factors to be individually critical to success. In this case, the 

overall risk category is defined by the average of the risk factors on each of the x- and 

y-axes. There is a balance between factors.

 Deem some of the factors to be more important than others, with no single factor 

dominating. In this case, the overall category is the defined by weighting the factors on 

each of the x- and y-axes.

There is no “cookbook” solution to deciding how to select the overall category because each 

project and stream presents different challenges and risks. What is required is consistent 

critical thinking and transparent, evidence-based decision making. The level of risk is often 

reduced when more data are available, or when the reviewer is familiar with the site.
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GOOD BEAVER DAM VIABILITY

POTENTIAL NEGATIVE IMPACTS

Habitat Enhancement, Recolonization, 

Population Management, Mitigation 

Techniques

POOR BEAVER DAM VIABILITY 

POTENTIAL NEGATIVE IMPACTS

Floodplain Excavation, 

Levee Set-Back, Revegetation 

GOOD BEAVER DAM VIABILITY

MINIMAL NEGATIVE IMPACTS

Recolonization, Reintroduction

POOR BEAVER DAM VIABILITY 

MINIMAL NEGATIVE IMPACTS

Floodplain Reconnection, Beaver 

Dam Analogues, Revegetation 

Increasing Negative Impact Potential

Decreasing Beaver Dam Viability

Stream Slope

<1% 1 - 3% > 3%

Valley Form 

Wide floodplain Narrow floodplain Confined channel

Channel Incision 

Yearly out-of-bank flow Occasional out-of-bank flow No out-of-bank flow

Riparian Corridor

Continuous/Wide Semi-continuous/Wide Discontinuous/Narrow Urbanized/Leveed 

Beaver Presence

Thriving Colony Evidence of Past Occupation No Evidence of Past Occupation 

Dominant Hydrologic Regime

Spring-fed Snowmelt Rain Rain-on-snow Convective Thunderstorm

Planning Context Coordinated Watershed Plan Stand-alone ProjectScaleMulti-Reach Scale Reach Scale Site ScaleAdjacent Land Us

e

Open Space Agricultural Rural/Suburban Urban/Industrial InfrastructureNone Bridges Culverts Intakes/Outlets Monitoring PlanAdaptive Management Monitoring only None

Figure 40: Beaver Dam Viability Matrix
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Chapter 11—Beaver Restoration Case Studies

Gregory Lewallen, Heidi Perryman, Carol Murdock, Mark Beardsley, Daniel Armichardy, Scott Jay Bailey, Bob 

Hassmiller, Sean Bistoff, David Helzer, Kendra Smith, Susan Firor, Janet Hohle, Scott Reid, Jessica Doran, Brad 

Johnson, Mike Claffey, Matt Weaver, David Kliegman, Julie Ashmore, Lauren Rich and Cathryn Wild

In this chapter we provide examples of restoration projects that have either incorporated 

beaver and/or beaver dam analogues into the restoration design and plans, or accommodated 

for beaver recolonization of the site after completion of the project. These examples provide a 

spectrum of ideas and approaches for using beaver and beaver dams for stream restoration 

projects. 

(1) Urban Beaver in Martinez California – Cohabitating with beaver in an urban setting

(2) Fanno Creek at Greenway Park, Beaverton, Oregon – Managing urban beaver

(3) Miami Wetlands Restoration Project, Oregon—Helping an existing beaver population.

(4) Camp Creek, Oregon--Log Weir Removal And Large Wood Placement Project, with an 

unexpected colonization by beaver

(5) Mason Flats Wetland Enhancement Project, Oregon—Helping an existing beaver 

population.

(6) Tualatin Basin, Oregon— Healthy Streams Plan Implementation—Helping an existing 

beaver population.

(7) Wet Meadow Restoration, Latah County, Idaho—Beaver relocation and Beaver Dam 

Analogues.

(8) Cucumber Gulch Preserve, Colorado—Encouraging beaver recolonization using Beaver 

Dam Analogues.

(9) Myers Creek, Washington Habitat Restoration Project-Beaver Dam Analogues and large 

wood.

(10) Hansen Creek, Washington Floodplain Restoration Project—Encouraging beaver 

recolonization

(11) Eastern New Mexico –Beaver Dam Analogues and beaver reintroduction

We recognize that there are numerous other ongoing beaver restoration efforts, including the 

Martinez project in California, the Elko project in Nevada, the San Rafael River project in Utah, 

the Pine Creek and Bridge Creek projects in eastern Oregon, the Scott Valley, Boise Creek and 

Child’s meadow projects in northern California, the Methow Valley,Yakima, Wenas Creek and 

Lands Council projects, all in eastern Washington, the Tulalip project in western Washington 

and many others which we have not described. We will be including descriptions of more of 

these projects in future versions of the Beaver Restoration Guide, along with a map showing 

the approximate locations. If you are interested in sharing your beaver restoration story, and 

the lessons you have learned, please contact Gregory Lewallan at gregory.lewallen@usask.ca.
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(1) Urban Beaver in Martinez, California by Heidi Perryman

How it started:

Martinez is the county seat of Contra Costa in northern California. It was also the final home 

of legendary ecologist John Muir and a national historic site. The town is located in the Arroyo 

del Hambre watershed, which drains into Alhambra Creek before flowing into the Carquinez 

Strait. The city utilizes the creek to funnel runoff from the streets and gutters. It passes 

through low-lying town for several miles and becomes tidal along the last 2500 feet before 

joining the strait.

In 2007 Martinez, California, had no intention of becoming an urban beaver case study. When 

a dam showed up, the immediate response was to pursue a depredation permit. With its tidal 

influence and low elevation, flooding was already a common problem downtown, and few 

business owners wanted to exacerbate the risk with an unwelcomed beaver dam.

Unfortunately, depending on your point of view, this particular beaver pair was highly 

visible, with a lodge near a popular restaurant and a dam visible from two high-trafficked 

bridges. Residents learned of the plan to 

depredate and immediately protested. There 

were petitions, news stories, and a candlelight 

vigil to protect the beavers. Meanwhile the 

arrival of summer meant the arrival of four 

adorable beaver kits, visible from the local 

Starbucks where residents could watch them 

play as they enjoyed their morning latte.

Beaver kits in Alhambra Creek: 

Photo by Cheryl Reynolds, Worth A Dam

The Beaver Dilemma:

Even after the arrival of the kits, downtown businesses were not dissuaded. They retained an

attorney who outlined the risks associated and claimed the city would be liable for any 

damage caused if they did not eliminate the beavers. In response, the city requisitioned a 

hydrology assessment of the creek from a consulting firm who calculated the added risk of 

flooding from the beaver dam as if it were a “concrete weir”. The dam, which they assessed as 

5 feet high, presented substantial risk and lowered the resilience of stream parameters. They 

recommended depredation.

Meanwhile, city leaders continued to pursue other options. Even though beaver relocation is 

illegal in California, they were able to arrange for the California Department of Fish and Game

(CDFG) to issue a special permit to relocate two of the six beavers onto tribal land following a 

necessary quarantine period. They were hopeful that this compromise would mollify resident 
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interest in the animals. The local Lindsay Wildlife 

hospital agreed to host the quarantine and a 

willing tribe in Plumas County was confirmed.

The meeting to discuss the final fate of these 

increasingly controversial beavers was held at the 

local high school performing arts center on 

November 7, 2007, because it was clear that 

attendance would exceed the limitations of the 

town hall. All 11 officers of the Martinez Police 

Department were on hand to control the crowd, 

and some 200 people showed up representing 

downtown, uptown and out-of-town. The meeting began with a report from the city manager, 

city engineer, a talk by CDFG and a review of the consultant report, after which the public was 

allowed to comment at a microphone with statements for up to three minutes.

More than fifty private citizens commented in favor of the 

beavers. Impassioned speakers ranged in age from 9 to 89. 

Although there were at least two comments at the beginning 

and end asking that the beavers be removed, the vast majority 

of the comments demanded that the city neither exterminate nor 

relocate the beavers, but find ways to maintain them safely in 

town. Many attendees had conducted their own research on 

flow devices or other possible solutions, contacting the Humane 

Society or the Sierra Club who vowed to offer assistance. One attendee pledged funds for a 

Clemson Pond Leveler and another for beaver birth control. Speakers included a former 

council member, local science teachers, mothers on the PTA and the homeless.

At the conclusion of 3 hours of public comment, the city council voted with two for and two 

against beaver removal with no tie breaker. The city proposed a subcommittee be formed with 

residents, biologists and flood control members to study the issue further. 

Implementation:

Three weeks later, a subcommittee consisting of two council members, a creek specialist, a 

flood control officer, a lawyer, a psychologist and a maintenance worker met. In 2007 there 

were limited online resources for humane beaver management. Each member was presented a 

binder of information on beaver biology, management, benefits, risks and options. The group 

was given 90 days to outline the pros and cons of trying to co-exist with urban beaver in a city 

setting. Issues addressed by the subcommittee included water quality, bank erosion, 

environmental impact, flooding, public opinion, population, mosquitoes and costs. There was 

a unanimous agreement to bring in Skip Lisle, President and Chief Scientist, Beaver Deceivers, 

LLC, who was already in the west for another commitment and allow him to address the 

subcommittee.

Mr. Lisle presented at the second meeting after assessing the situation in the field. He noted 

that at issue was the vertical growth of the dam and recommended the ‘Castor Master’ design 
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he had used in similar situations. There was discussion of costs and permits, but concern for 

the severe storm predicted for January hastened things along. On January 2, 2008, Mr. Lisle 

was assisted by public works in lowering the dam and installing the Castor Master -- and not a 

moment too soon, because the driving storm soon followed.

Looking back:

Despite the success of the flow device, 

downtown businesses continued to worry 

about flooding. The psychologist

participating in the project realized that 

changing beaver behavior was going to 

be easy. It was changing human behavior

that was going to be hard.

There were a grand total of two steps necessary to effectively change beaver behavior. 

1) Installing the Castor Master, which cost the city approximately $10,500 for labor, 

materials, and travel for Mr. Lisle from Vermont.

2) Wire wrapping or sand-painting trees, which cost volunteers a total of $300 and was 

repeated as necessary to prevent chewing. We followed the abrasive painting recipe on 

the Beaver Solutions Website and repeated every 18 months.

The following steps were applied and reapplied to effectively change human behavior. 

A. Education in the form of town halls, outreach and community lectures.

B. Child education through fieldtrips, activities and art projects.

C. Media education to influence information distribution.

D. Media presence on radio and television news.

Beaver story makes nightly Fox National News 2008.

E. Annual beaver festival to influence and educate.

F. Citizen steward projects, such as planting trees, to 

encourage ownership.

G. Constant public input in the form of cards and letters to city leaders.
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The success of steps 1 and 2 were 100% effective and took about 

1 month to complete.

The success of steps A – G were moderately effective in helping 

people influence public decisions, but have required constant 

reinforcement over the past eight years. 

After nearly a decade of this work I can conclude without a 

doubt that Beaver Behavior is much easier to change than 

human behavior! 

Green Heron catches Sacramento Splittail in Alhambra Creek

Was it worth it?

The beaver-generated benefits to Alhambra Creek 

include: new species of bird, fish and mammals (from 

wood ducks, to Sacramento splittails and mink). A 

creek which once went dry every summer now has

year-round flow, and several occasional species became 

regulars, such as western pond turtle, belted kingfisher, 

green heron, and otter.

Otter standing on flow device in beaver habitat.

The beaver-generated benefits to the residents of 

Martinez include increased social cohesion, a 

greater awareness of the watershed in general, 

greater ecological awareness for children and 

adults, and a reminder that everyone can help 

influence city outcomes when they are willing to 

work together. The beaver festival has become one 

of the largest wildlife events in the state and draws 

an attendance of 2,500. Other benefits include a 

broader public profile, increased tourism and 

recognition of Martinez as one of the first cities in 

the nation to successfully promote urban beaver 

management. 
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Children and adults paint tiles which became a mural on a bridge over the creek where the beaver live. 
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(2) Fanno Creek at Greenway Park, Beaverton, Oregon by Carol Murdock

Clean Water Services, Tualatin Hills Parks and Recreation District, and Metro

Case study prepared by: Carol Murdock and Bruce Barbarasch

Context:

Fanno Creek flows through Greenway Park between SW Hall Boulevard and SW Scholls Ferry 

Road in Beaverton, Oregon. The Fanno Creek Regional Trail runs along Fanno Creek and 

connects Greenway Park to additional park properties and to cities to the north and south. The 

park provides visitors with a wide variety of recreational opportunities including: bicycling, 

running, basketball, disc golf, playgrounds, and access to nature and wildlife viewing along 

several sections of restored natural area corridor. 

In 2008, Clean Water Services, working in partnership with Tualatin Hills Parks and 

Recreation District (THPRD)’s Natural Resources Department and Metro’s Nature in the 

Neighborhoods Grant Program, initiated a multi-year project to enhance the riparian portions 

of Greenway Park. Over the past eight years more than 140,000 native trees and shrubs have 

been planted at the site. The enhancement of the mixed oak-ash woodlands, wetlands, and 

riparian areas provides diverse native habitat for a wide range of wildlife including 

endangered steelhead, herons, osprey, egrets, waterfowl, cavity-nesting birds, songbirds, and 

beavers.
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Figure 41: Fanno Creek – Greenway Park.

Issue:

Over the last 20 years beavers have been actively creating a series of dam complexes that have 

effectively connected the formally degraded and incised Fanno Creek channel to its historical

floodplain. Because the majority of Greenway Park lies within the 100 year floodplain, the 

additional beaver dams caused portions of the regional trail to become inundated year round. 

This limits public access to portions of the regional trail network that runs through the park. 

Figure 42: Active beaver dam at Greenway Park.
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Figure 43: Inundation of portions of the regional trail system.

Goals and Objectives:

THPRD has conducted an extensive outreach to park users and adjacent property owners 

regarding trail access and is actively educating the public about the positive effects of beaver 

ponds including: habitat for birds, fish, turtles, and amphibians as well as stormwater 

mitigation and groundwater recharge. The response from the community has been largely 

positive but because THPRD and CWS are actively partnering on additional ecological 

enhancement projects located on properties managed by THPRD, it’s important to develop a 

coordinated approach to beaver outreach and education as well as responsible beaver 

management in areas where the potential for conflicts between park users and beaver activity 

is high. By gaining a better understanding of the potential impacts that beaver activities have 

on urban stream systems, we can provide better information to park users and to other 

organizations that are also trying to balance the multitude of benefits that beavers bring to the 

community with potential impacts to human infrastructure. CWS is currently collaborating 

with several regional partners on initiatives that are focused on gathering additional 

information about beaver dams and beaver activities including: quantification of the 

environmental benefits beavers provide to the community; analyzing and identifying potential 

areas of human/beaver conflict; and providing additional tools for beaver management in 

urban areas. 

Strategies: 

1. Using Beavers as a Strategy for Stormwater Management

To better understand the effects of beaver dams and beaver activities in urban stream systems, 

several regional partners including Portland State University, The Wetlands Conservancy, 
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USGS, THPRD and Clean Water Services are collaborating on a two year project to measure 

reach-level impacts of beaver dams on urban stream hydrology, geomorphology, 

groundwater recharge, and water quality as part of an innovative approach to managing 

stormwater runoff. USGS scientists will deploy monitoring instrumentation at several known 

beaver dam locations within the urban areas of Washington County in the summer of 2016. 

The data and information collected as part of this study will inform policy development 

concerning the incorporation of beaver activities as part of a comprehensive strategy to meet 

specific provisions of the Clean Water Act. The study will also include citizen-science based 

data collection (amphibians, turtles, and birds) to better quantify beaver dam impacts on 

biodiversity. 

2. Identifying Areas Where Beaver/Human Conflicts 

Many of the public land managers in the Tualatin basin are dealing with conflicts that 

invariably occur between beaver and human infrastructure. The ability to communicate the 

benefits that beaver dams provide to the community in terms of habitat for wildlife and flood 

mitigation/storage must be paired with responsible beaver management in areas where 

conflicts do occur. CWS is working closely with USGS staff and graduate students from 

Portland State University to inventory existing beaver dams and predict where these conflicts 

might occur utilizing the Beaver Restoration Assessment Tool (BRAT). The tool can be used 

to predict the likelihood of beaver colonization in a given area based on several characteristics 

such as stream gradient, flow velocities, and riparian vegetation and can identify where 

impacts to infrastructure are likely to occur based on proximity. The tool was originally 

developed by Utah State University and has been used in the Escalante River Basin of SE Utah. 

The ability to adapt the tool for use in an urban environment will be investigated as part of the 

study. Running the tool for the Tualatin basin should provide CWS and its regional partners 

with preliminary information that can be ground-truthed against the inventory of known of 

beaver dam locations.

Outcomes/Results/Monitoring:

Final selection of beaver-influenced stream reaches for the study is being conducted now. The 

expectation is to have a preliminary report on the first summer’s monitoring data in the near 

future. Preliminary results from the BRAT tool should also be available at that time. In the 

meantime, CWS will continue to work closely with its regional partners to provide education 

and outreach to the public regarding the many benefits of restoring beaver to landscape in the 

Tualatin.
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(3) Miami Wetlands Restoration Project, Oregon

Tillamook Estuaries Partnership, Scott Jay Bailey, Project Manager

Figure 44: 2014 aerial photo of the site showing locations of monitoring wells and two beaver dams

Location and Description

The Miami Wetlands Restoration Project is located along the Pacific Coast in Tillamook 

County, Oregon. The approximately 58-acre wetland straddles the Miami River near its mouth 

at Tillamook Bay. The site is located well below head-of-tide and elevations within the 

wetland portion of the site range from approximately 6 to 12 feet above sea level. The site is 

isolated from a downstream tidal wetland at the river mouth due to U.S. Highway 101 and, 

although elevations within the site are within the range of tidal amplitude, water quality 

monitoring indicates that fresh water predominates. Water levels are influenced by 

precipitation, beaver activities and tidal fluctuations.

Restoration Goals

 Improve connectivity between on-site wetlands and the mainstem Miami River

 Increase the quantity and quality of on-site aquatic habitats
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 Restore the historical character of on-site vegetation

 Restore Hobson and Struby creeks to a more natural configuration, further away from 

the U.S. Highway 101 corridor

 Enhance riparian vegetation along the Miami River to increase shading and provide a 

source of wood for future in-channel large wood recruitment

Construction began in 2010 and concluded in 2011, and returned the function of the on-site 

wetlands through reconnection of the tidally influenced hydrology to the mainstem Miami 

River and improving conditions in a freshwater stream channel running through the site. This 

was accomplished by filling drainage ditches and creating a series of new channels 

throughout the site, including a meandering stream channel and several tidally-influenced 

channels. Planting followed construction activities and incorporated a variety of native trees, 

shrubs, graminoids and forbs. The plant palette included beaver-preferred species such as 

willows (Salix spp.) and black cottonwood (Populus trichocarpa).

Beaver were present on the site before the project started and occupied all pre-construction 

channels. A few dams were present pre-construction, but beaver activity increased postconstruction apparently as willow distribution and abundance expanded due to planting of 

pole cuttings. As a result, the number of beaver impoundments has increased substantially.

The project plan did not specifically involve beaver, but the expectation was that they would 

remain after construction was completed and continue to modify the site. No beaver were 

removed from or transplanted to the site. Almost all the tree plantings were protected from 

beaver herbivory by 4-foot high chicken wire cages. Pole cuttings, shrubs, graminoids and 

forbs were not protected. While protected trees have remained relatively undisturbed by 

beaver, herbivory of other plantings (especially pole cuttings) has been very common.

However, because the planting strategy incorporated large numbers of plants, beaver 

herbivory has not driven plant survival to unacceptably low levels.

In June of 2013, beaver rapidly built a bank-high, channel-spanning dam at the confluence of 

two small stream channels that created a large pond and lateral overbank flooding (Figure 44).

This dam has raised the local water table and moderated fluctuations between precipitation 

events as compared with pre-project conditions (Figure 45). Beavers quickly developed small 

channels extending outward from the pond to increase their forage area. During summer 2014, 

another channel-spanning dam was built (Figure 44), which has also included lateral channel 

development and resulted in over-bank flooding, pushing water laterally and increasing the 

area of soil saturation, and moderating water level fluctuations (Figure 46). Most channelspanning dams seem to be situated at or near the confluence of streams and side channels, and 

most construction activity has been associated with the stream channel and not the tidal 

channels. Beavers have also built small check dams to control the new overland flows that 

resulted from these larger dams. Beaver are actively consuming herbaceous vegetation, 

willows and alders at the site, with primary dam construction material of willow branches 

with leaves, mud, and reed canary grass used as fill and sealant.

Monitoring indicates that dam-building activity has substantially increased the amount of 

surface and subsurface water present on the site. Fish surveys show increased numbers of 
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cutthroat trout and coho salmon, especially in the beaver ponds and around constructed large 

wood structures. Water temperature monitoring indicates that surface and subsurface water 

temperatures at the site are consistently below Oregon Department of Environmental Quality 

maximum temperature standards for salmon and trout spawning and rearing/migration 

periods (Oregon Administrative Rules 340-041-0028). 

Predicting where beavers would build dams is very difficult. As a result, some of the plantings 

(primarily shrubs and conifer trees) were indirectly killed by beaver from the inundation 

following dam construction. However, the benefits from the increased surface and subsurface 

water, fish habitat, and complexity that can be attributed to the dam-building activity 

outweighs the loss of the small percentage of plantings from flooding. To compensate for these 

losses, mortality replacement planting in these areas has incorporated plant species 

compatible with long-term inundation. As with beaver herbivory, this indirect mortality has 

not driven plant survival to unacceptably low levels. 

Overall, the managers consider the project to be a success and the beaver activity a welcome 

complement to the project. 

For more information regarding this project including baseline and interim monitoring 

reports, Miami River Watershed Assessment (2001), and other reports go to: 

http://www.tbnep.org/habitat-enhancement-and-restoration.php

Figure 45: Data from monitoring well #5 showing a moderation of the water table following the 

construction of a beaver dam in the nearby channel
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Figure 46: Data from monitoring well #6 showing a rise in the local water table following 

construction of a beaver dam in the nearby channel
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(4) Camp Creek Log Weir Removal And Large Wood Placement Project (2011-2014) 

Malheur National Forest, Blue Mountain Ranger District, Bob Hassmiller, Zone Hydrologist. 

Case study prepared by Dan Armichardy, United States Forest Service

Location and Description

Camp Creek is a 6th order creek that drains into the John Day River Basin. The John Day 

River Basin is considered the “most biologically diverse river system and a globally important 

stronghold of wild salmon” because the John Day River is the longest free-flowing river in the 

Columbia basin, and is mostly devoid of hatchery influences. The Camp Creek watershed has 

been rated as high priority for habitat protection and restoration within the subbasin by the 

Mid-Columbia River Steelhead Conservation and Recovery Plan. This Plan identified limiting 

factors that impact steelhead production and ecohydrological processes and functions in the 

Camp Creek watershed: degraded riparian communities, floodplain connectivity and 

function, channel structure and complexity, water quality (stream temperature), and altered 

hydrology and sediment routing, all of which are integrally related and play critical roles in 

the creation and maintenance of quality fish habitat. Past practices of beaver trapping, heavy 

livestock grazing, riparian logging and associated railroad grade construction in the valley 

bottoms are the dominant actions that disrupted process and functions and led to the listed 

limiting factors. Camp Creek is considered the highest priority watershed by The John Day 

Subbasin Revised Draft Plan. In response to these designations a 2008 Watershed Restoration 

Action Plan (WRAP) was developed as a road map to complete high priority restoration 

projects. These projects have been planned with the intent to meet the desired conditions 

stated in the WRAP. Threatened Mid-Columbia River summer steelhead and spring Chinook 

salmon, take up residence in Camp Creek and its tributaries during various life stages. 

Summer steelhead adults use Camp Creek and its tributaries as crucial spawning grounds 

from April through June. The fry emerge by mid-July, and the juveniles reside in Camp Creek 

and tributaries for 1 to 3 years, migrate to the ocean, and return as adults to spawn. Spring 

Chinook adults spawn in the lower reaches of Camp and Lick Creeks. Juveniles use the habitat 

for 1 to 2 years, and then make their way to the Pacific Ocean. Chinook juveniles hatched in 

the Middle Fork John Day River use Camp Creek as thermal refuge during the hot summer 

months when the Middle Fork John Day River temperatures rise. 

One of the primary goals identified within the Camp Creek WRAP included the removal of 

approximately 238 log weirs within Camp Creek watershed. Large wood structures and trees 

with rootwads were placed in Camp Creek within the same vicinity of log weir removal in 

2011 (see Figure 47). 123 log weirs were removed or modified during this work in the lower 

sections of Camp Creek. 

Restoration Objectives: 

 Reduce the width of the active channel

 Increase floodplain connectivity

 Increase roughness to induce gravel deposition
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 Increase area of quality pool habitat

Stream channels within the reaches where log weirs were located have narrowed and 

vegetation has colonized exposed stream banks. The majority of pools created through 

excavation have been maintained by instream wood. Gravel sorting is evident throughout the 

reaches that were predominantly plane bed with an armor layer of cobble that functioned as a 

transport reach (slope 0.017). Based on this evidence the project continues to improve MidColumbia River Steelhead habitat deficiencies identified within the Camp Creek WRAP.

Unforeseen Benefits

In 2014, beaver moved into a portion of Camp Creek where log weirs were removed, pools 

were excavated, and wood was added (see Figures 51 and 52). While historical beaver 

evidence was present within Camp Creek, transient beaver activity and dams have been noted 

but no prior large dams, such as those observed in 2014, were documented within lower Camp 

Creek. Many of the dams that appeared in 2014 were keyed into placed wood or boulders for 

added stability and persistence (Figures 48-50). Additionally the beaver dams backwatered the 

placed wood structures and the excavated pools increased the depth upstream of the dam to 

over 5 feet in places. Observations indicate beaver are using the wood structure locations as 

dens and the deep excavated pools as food caches for over wintering. During the spring of 

2015, several smaller dams were breached leaving large gravel patches (built by beaver for 

dam construction). Several steelhead were observed constructing redds in these breached 

areas. This provides an example of combined salmon/beaver because the same limiting 

factors affecting salmonids may also be limiting beaver—the two are not exclusive, but share a 

common beneficiary relationship. Dams anchored to large wood tended to be taller, had more 

internal stability and had a larger hydrologic zone of influence (see Figures 48 and 50). 
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Figure 47: Log Weir Removal from Reach 4 of Camp Creek before (top left), immediately after (top 

right), and 3 years later (bottom)

06/25/2011

06/2014
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Figure 48: Medium size (< 12 inch) diameter ponderosa pine placed in mid-channel in 2011 following log weir 

removal. Beaver dam has incorporated rootwad into center of dam (6/15/2014).

Figure 49: Existing rock placed mid-channel during log weir removal 2011 has been incorporated into 

beaver dam (6/15/2014)
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Figure 50: Beaver dam with rootwad incorporated (12/15/14)

Figure 51: Smaller beaver dam built at pool tail out without wood (12/15/14).
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Figure 52. Valley bottom being inundated with moderate flood because of beaver dam influence 

(12/22/14). Same dam as Figure 52.
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(5) Mason Flats Wetland Enhancement Project

Sean Bistoff, Capital Project Manager, City of Portland Environmental Services

Figure 53: 2015 aerial photo of the site showing locations of old, reconstructed, and newly 

constructed beaver dams. Figure courtesy of City of Portland, Environmental Services.

Location

NE Mason and Airport Way in the Big Four Corners Natural Area of an industrial 

neighbourhood, Portland, Oregon.

Restoration Goals

 Improve Columbia Slough water quality through stormwater treatment and 

temperature reduction of runoff and effluent entering the wetland restoration site

 Improve habitat for native species (e.g. willow flycatcher, western painted turtle, red 

legged frog)

 Increase floodplain function and floodwater storage

 Increase native vegetation

 Protect and enhance wetland habitat
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Site Description

The project site is a 27-acre marsh and scrub wetland, which discharges to the Columbia 

Slough in an industrial area in Northeast Portland. The site consisted of a drained and 

abandoned agricultural field of reed canary grass adjacent to a partially functioning wetland 

mitigation site. The project directs water back onto the drained field, increasing the water 

retention on site. Two sets of weirs and a network of engineered swales and vegetated 

channels were constructed to divert spring flow and treated stormwater onto the field. During 

design, several existing beaver dams were observed in the project area (Figure 53). Rather than 

designing a system that would be at odds with beaver activity, and since all of the project 

goals are in align with the effects beaver dams, a flexible design was developed to allow 

modification and enhancement by beaver. 

Data collected by the Bureau of Environmental Services show that beaver activity has 

increased since project completion, and has improved the overall project effectiveness. For 

example, beaver dams have remedied a site grading problem that might have otherwise 

required additional work, and a complex of new dams has increased the overall wetted area 

and detention time on the site. In addition, beaver have forced overland flow onto an existing 

willow glade directly adjacent to the restored site that is slightly higher in elevation. This has 

allowed access to important food and construction materials leaving the newly planted, and 

exposed, willows and other native plantings relatively unbrowsed by the beaver, thus giving 

them time to mature. Since the site is inherently difficult to access with equipment, had past 

beaver occupancy, and is suitable habitat for many different species supported by beaver 

modification, it has been successfully designed to be flexible and to allow continued beaver 

modification without intensive maintenance or management. Furthermore, located in an 

industrial area of a major metropolitan city, this site is a great example of how beaver can be 

utilized in restoration projects where perceived risks of human-beaver conflict may seem high. 

Utilization of an adaptive management plan, post-project monitoring, and ensuring that 

adjacent properties are safe from beaver modifications and inundation from dams have 

contributed to this projects success.
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(6) Tualatin Basin, Oregon—Healthy Streams Plan Implementation 

Kendra Smith, Restoration Ecologist

Location

The Tualatin Basin in northwest Oregon drains 712 square miles from the forests of Oregon’s 

Coast Range, Tualatin Mountains and Chehalem Mountains, to the valley floor dominated by 

agricultural lands to the west and densely populated areas to the east, including the cities of 

Hillsboro, Tigard, Tualatin, Beaverton and portions of southwest Portland. Protection and 

restoration of the surface waters of Tualatin Basin began in the 1970s, with upgrades to 

wastewater treatment plants. In the late 1990’s efforts to improve the quality and connectivity 

of the steam network were initiated.

Enhancement Goals

Large-scale watershed enhancement, to advance water quality, water quantity, and habitat 

goals were guided by the Healthy Streams Plan (Clean Water Services, 2000-2005) and other 

watershed planning efforts developed in 1995 to 2000. Enhancement projects were designed 

and implemented to support recovery of stream processes and function, including: 

 Restoring degraded riparian areas by removing invasive plants and revegetating with 

native plant communities

 Improving stream function by remeandering straightened and incised streams and 

placing large wood

 Reconnecting floodplains and the streams by encouraging overbank flows, 

reconnecting side channels, and removing fish barriers

 Engaging with local maintenance staff and USDA’s Animal and Plant Health 

Inspection Service (APHIS) to aggressively remove nutria, while allowing native 

beaver to persist in the system

Projects started in 1996 and are ongoing, as part of Clean Water Services watershed 

management program. A majority of the streams treated in the Tualatin basin had highly 

degraded riparian areas dominated by non-native species. Several reaches were highly incised 

resulting in increased stream power, channel erosion, and floodplain disconnect. Beaver 

activity and summer water levels were low throughout the watershed; only 25 reaches out of 

506 assessed (representing 338 miles of streams) in 2000 had documented evidence of beaver 

use (4.9% of the reaches)(Watersheds 2000 Dataset, Clean Water Services, 2000). 

Riparian restoration, barrier removals, channel remeanders and large woody debris placement

were the focus through the first 8 years of the program. But in 2005, an informal agreement 

was negotiated between Clean Water Services, member cities, Washington County and 

APHIS, to redirect trapping activity to non-native species (nutria) and, stop the trapping of 

beaver in the urban reaches of the Tualatin basin. By 2010, the evidence of the release of 

trapping pressure on beaver were already being seen and increases in riparian vegetation 

seemed to be supporting the beaver activity (i.e. dam and lodge building) in the urban areas
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(Figure 54). By 2014 there was a substantial difference in the amount of native riparian 

vegetation, in-stream water, and over-bank flooding onto the floodplains in the urban areas 

versus the rural areas. The Willamette Riparian Revegetation Effectiveness Study (BEF, 2015) 

completed a sub-study of 40 sites within the original 509 reaches, confirmed beaver use at 25 

sites (62.5% of those assessed), and a local park district documented another 26 sites in 2012 

that were not occupied in the 2000 assessment. At one urban site, a pond leveler was installed 

where beavers have constructed channel and floodplain spanning dams that pond enough 

water to inundate both the floodplain and a bike path. The pond leveler helps reduce the 

flooding of infrastructure by regulating the amount of impounded water.

Figure 54: Photo of urban reaches (within the yellow lines) showing limited beaver activity in 2005 

(above) and increased beaver activity in 2015 once trapping pressure was removed (below). Figures 

courtesy of Kendra Smith.
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Lethal removal of beaver through trapping and hunting continues in rural areas where beaver 

activity is not well documented in the Tualatin Basin, except at enhancement sites. Sites with 

limited food sources and water withdrawals during summer low surface flows, are less than 

ideal locations for beaver to occupy and may be a limiting factor in addition to trapping 

activities.

Utilizing beaver to help restore streams in urban areas requires a thoughtful, adaptive 

management approach. Regular site monitoring, open communication and collaboration with 

all interested parties can reduce the risk of human-beaver conflicts (i.e. flooding of 

property/infrastructure). This project is great example of how beaver can be used to help 

restore streams in urban and suburban settings. 
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(7) Wet Meadow Restoration, Idaho 

Susan Firor, Principal Restoration Engineer, TerraGraphics Environmental Engineering, Inc.; 

Trish Heekin, Resource Conservation Planner, Latah Soil and Water Conservation District; 

and Janet Hohle, Project Manager, Clearwater Focus Program, Idaho Office of Species 

Conservation

Location 

Latah County, Idaho

Restoration Goals

 Reconnect streams to wet meadows

 Improve/increase summer rearing habitat for steelhead

 Aggrade incised stream reaches

 Redirect flow into historical channels and out of old borrow ditches formed during 

construction of railroad berms in late 19th – early 20th centuries

 Increase local aquifer recharge

 Raise groundwater elevations

 Transform ephemeral streams to intermittent or perennial flow where possible

 Restore beaver habitat

The restoration site consists of approximately four stream miles on several forks of a tributary 

to the Potlatch River. The site is primarily on private land owned by a single landowner. Many 

of the existing beaver meadows have become hydrologically disconnected from their stream 

systems due to lack of beaver dams and large wood impoundments, incision of streambeds, 

and channel diversions into old borrow ditches. There are signs of historical beaver activity in 

this region as well as recent beaver activity; however, the beaver population appears to be

very low, with some reaches lacking any recent beaver activity. Anecdotally, the beaver seem 

to abandon areas within a year or two, either moving to new areas or being trapped out.

Although some lodges have been built in this area, most beaver appear to be bank dwellers.

Riparian vegetation for both food and construction material is available in many reaches; 

however, some meadow reaches are completely devoid of woody vegetation. Beaver trapping 

was prohibited in this watershed for a 10-year period but was reopened to trapping in 2011. 

Although most of the project is on private land, which is posted no trespassing, the landowner

believes there is still significant trapping pressure.

Currently, the Idaho Fish and Game Department authorizes kill trapping of nuisance beavers, 

but they will refer affected landowners to a small group of people who live trap and then 

release the “nuisance” beavers in suitable habitat. To date, the group has live trapped two 
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beaver families (11 beavers total) from nearby sites and released them within the subject 

restoration property.

Restoration at this site has included installation of two types of beaver dam analogues (BDAs) 

(see Figures 55 and 56). Earthen BDAs are used to divert flow back into historical channels 

and to develop wetland cells along the degraded channel (Figure 1). Other BDAs consist of

cedar stakes 3–6 feet tall, driven halfway into the ground and woven with willow cuttings and 

other brush materials (Figure 56). Beaver have not modified or maintained any of these 

structures yet. However, the BDAs are functioning as anticipated by slowing and impounding 

water and sediment, which has increased the area of saturated soils during spring runoff. To 

date, FBDs have been placed in small seasonal side channels and along potential avulsion 

pathways. Placement was determined primarily in response to hydraulic needs to protect the 

in-stream BDAs. Future BDA installations are planned for main channel locations where they 

slow flow velocities, pool water, and trap sediment, ultimately prolonging saturation of the 

wet meadows well into the dry summer season. 

Monitoring is underway in five meadows within this watershed to determine whether the 

meadow restoration projects are, as anticipated, raising the local water table and retaining 

water for longer duration than prior to implementation.

The project organizers believe that utilizing beaver to restore wet meadow habitat is gaining 

widespread interest across the western United States. Often, however, the desired effects of 

beaver dams can be outweighed by negative perceptions from landowners and managers. This 

project provides an example of how BDAs can be utilized to achieve landscape improvements 

similar to those resulting from natural beaver activities in areas where trapping pressure 

keeps populations low. Installing BDAs initiates long-term restoration of the site, promoting 

aggradation of sediments, increased water table, saturated soils, and better survival of woody 

riparian plants. These conditions could attract beaver by providing food and cover, or support 

beavers reintroduced to the project area. In addition, this project’s positive effects on the 

landscape and available livestock forage have helped to assuage cattle operator concerns 

about potential flooding.
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Figure 55. Earthen BDA and Wetland Cell in second growing season after construction.

Figure 56. BDAs after peak flow constructed with posts driven into the streambed and woven with 

wicker weaves.
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(8) Cucumber Gulch Preserve, Colorado

Scott Reid, Town of Breckenridge; Mark Beardsley and Jessica Doran, EcoMetrics; Brad 

Johnson, Johnson Environmental Consulting; Mike Claffey, Claffey Ecological; Matt Weaver, 

Five Rivers; Breckenridge Ski Area 

Location and Description 

Cucumber Gulch Preserve is 

located near the town of 

Breckenridge, Colorado at the base 

of the Breckenridge Ski Area 

(Figure 57). It is a first order 

headwaters wetland system at 

about 10,000 feet elevation. The 

wetland area is designated an 

Aquatic Resource of National 

Importance (ARNI) by the US EPA 

because it supports unusually high 

biodiversity for the area. It is 

managed as a wildlife preserve.

Problem 

The contributing watershed for the 

wetland is entirely within the

Breckenridge Ski Area (Figure 58). 

Ski area developments include 

base area developments, imported 

water (snowmaking), clear cuts 

(ski runs), miles of service roads, 

and a highly modified drainage 

system. Runoff from the 

watershed is collected from a 

system of ditches and drains into a central point where it is routed under road fill to the 

Cucumber Gulch wetlands through a single 60 inch diameter culvert known as Boreas Creek.

The combined effect of these stressors is an altered hydrology that is both augmented (more 

water) and flashier (higher magnitude and shorter peaks) and a severely increased sediment 

supply to the wetland.

Figure 57: Location of Cucumber Gulch Preserve in Summit 

County, Colorado
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Sediment routed from the ski area to 

the wetland through the pipe 

eventually filled beaver ponds with as 

much as four feet of deposition (Figure 

59) and beavers were unable to raise 

the height of dams fast enough to keep 

up. Beavers eventually abandoned the 

site and were completely absent by the 

early 2000s. Though mostly full of 

sediment, the beaver dams continued 

to function for some years, spreading 

water among a system of tiny 

distributary channels. But without the 

daily maintenance by beavers, the 

ancient dams began failing after 2007 as 

nick points formed and eventually 

head cut through the dams. Head cuts 

migrated rapidly upstream through 

deposition in the ponds and wetland 

forming a deeply incised channel 

(Figure 60). This effectively cut off the 

water supply to the wetland, and the 

wetland began shrinking. By 2011 all of 

the ponds in this portion of the 

preserve were dry, Boreas Creek had 

become a deep incised gully, and the 

wetland was a fraction of its original 

size and still shrinking (Figure 61). 

The community would like to maintain the Preserve in as natural condition as possible to 

support the greatest number of native plants and animals, so a restoration project was 

conceived in 2012. The guiding image for restoration is to restore the wetland habitat of 

Upper Cucumber Gulch to its previous extent and condition by mitigating external stressors 

(hydrology and sediment), repairing the incised channel, and restoring beavers.

Figure 58: The contributing watershed (blue) to the 

Cucumber Gulch Preserve (purple) is entirely within the 

Breckenridge Ski Area and severely modified to meet 

that purpose
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Figure 59: A beaver pond that is completely full of sediment that was routed into the wetland from 

the contributing watershed prior to restoration. The accelerated rate of sediment accumulation in 

ponds exceeded the ability of beavers to keep up, so they abandoned the site

Figure 60: Once dams failed, a channel formed and immediately began head cutting. These photos 

show the Boreas Creek channel in different stages of incision, initial channel formation (left) and 

advanced incision (right)

Restoration Goals 

The overarching goal for this project is to restore the former extent and condition of wetland 

habitat. Specific goals describe the means to that end: 

• Mitigate hydrologic impacts from contributing watershed 

• Mitigate allochthanous sediment supply from contributing watershed 

• Restore the incised Boreas Creek channel to a native anastomosed condition

• Restore a self-sustaining beaver population
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Figure 61: This photo series shows the sequence of wetland degradation after beaver abandoned the 

site in the early 2000s. Full ponds and active channels are depicted in blue. Dry ponds and channels 

are shown in orange. Pink shading depicts the extent of wetlands based on Army Corps of Engineers 

delineation criteria. The red line shows the extent of the newly formed incised Boreas Creek channel. 

The background imagery is from 2011. 

Strategy 

It is clear that beavers were the primary agent that formed and maintained the stream and 

wetland in Cucumber Gulch, so the strategy is focused on recovering a self-sustaining 

population of beavers. The first step towards beaver recovery is restoring suitable habitat. 

The wetlands were just recently dried, so most of the hydric vegetation was still in place, 

including a sufficient supply of woody vegetation for beaver food and building material. The 

limiting habitat factor was deep water cover, and restoring deep water to the site was a twopart process involving the removal of accumulated sediment from the ponds and repairing 

the breached dams. 
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Removing allochthanous sediment was 

acieved by excavation to haul several 

hundred cubic yards of material, but the

strategy for repairing the dams required 

an approach a bit different from 

traditional BDAs. The dams on this site 

are so ancient that their cores have 

mostly decomposed into mineral and 

organic soil, so the dam breaches were 

patched with coir-wrapped soil lifts 

interwoven with live willow stems 

(Figure 62). On one dam, a PLWW was 

constructed across the top of the dam to 

fortify a nick point in the repaired dam 

to (hopefully) entice beaver to take over 

maintenance (Figure 63). These 

treatments were implemented in the fall 

of 2012. 

Secondary goals of the project involve 

mitigating external stressors, 

particularly the altered hydrologic and 

sediment regimes caused by land use in 

the contributing watershed (which is a 

ski area). Addressing these issues is 

paramount for long term success since 

these impacts are likely responsible for 

the original collapse of the system and 

will continue to impact restoration 

efforts if they are not alleviated or 

mitigated. Alleviation of these stressors 

at the source is not a feasible option, so 

both problems were simply mitigated to 

the greatest extent possible at the head 

of the wetland. The first beaver ponds in 

the system are being used to spread 

flows across the wetland area and to 

capture incoming sediment. Maintenance staff is on call to remove sediment that accumulates 

as a delta at the inlet to the first pond as needed, before it starts filling the pond proper. The 

first clean-out is scheduled for spring, 2015 to remove about 40-50 cubic yards of sediment. 

Several treatments were applied to the incised Boreas Creek channel in 2013 including two 

BDAs, but the ultimate strategy is to rely on beavers to complete the restoration. Since most 

of the incoming flow is now spread across the wetland and no longer consolidated within the 

incised channel, we suspect that beavers will easily be able to build dams. If this proves not to 

be the case, additional BDAs will be constructed. 

Figure 62: Breached dams were “plugged” with soil 

lifts wrapped in coir fabric and sod interwoven with live 

willow stems

Figure 63: A PLWW was constructed on one repaired 

dam to temporarily fortify a nick point while we were 

waiter for beaver to reoccupy the site
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The initial strategy for 

restoring a beaver 

population was to rely on 

natural immigration of 

beavers to the site from 

nearby locations, but we 

were able to take advantage 

a fortuitous opportunity to 

host a recently captured 

nuisance beaver (Figure 64). 

We named him Franklin and 

released him to one of the 

recently restored ponds in 

summer 2013, where he took 

advantage of a supply of 

aspen that was set out for 

him and fortunately decided 

to stay. In a matter of days, 

Franklin had begun packing 

mud and sticks on the dam face, apparently having taken residence in an old abandoned 

bank lodge. Later that season several additional beavers returned to the site, and most of the 

dams on the site were being fully maintained by beavers before winter of that year

Monitoring and Results 

The functional condition of the wetland was rated as severely impaired in 2011 using the 

Functional Assessment of Colorado Wetlands (FACWet) version 2.0, and a delineation at that 

time showed that wetland extent was severely reduced. Quantitative hydrology, soils, and 

vegetation data confirmed these results. Beaver population surveys showed no indication of 

beaver activity on the site in 2011 or 2012. To develop a quantitative monitoring plan, we 

predicted what the change in FACWet variable scores would be if the treatments were 

successfully implemented and beavers returned to the site. Prognosticated scores provided a 

benchmark for setting specific objectives, targets, and success criteria by which the 

effectiveness of wetland restoration could be judged (Table 9), and an array of monitoring 

points was established across the site to track changes in hydrology, soil, and vegetation 

parameters (Figure 65).

Figure 64: The project relied on natural beaver immigration to the 

site, but one trapped beaver was released at the site in 2013
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Table 9: A monitoring plan was developed to track the effectiveness of restoring functional condition 

of the wetland based on FACWet variable scores. Pre-project and target scores are shown, along with a 

description of success criteria and monitoring activities. 

FACWet 

Variable 

# 

Variable 

Description 

Preproject 

score

Target 

score 

Success Criterion Monitoring 

1/2 Connectivity C C N/A N/A 

3 

Buffer 

Capacity D D N/A N/A 

4 Water Source D B 

1. Incoming water from Boreas 

Cr. is spread laterally in a full 

“spreader pond” that feeds multiple 

distributary channels across the width 

of the complex. 

1. Observation, 

photos, streamflow 

monitoring 

5 Water 

Distribution D- B 

1. Historic extent and depth of 

pond habitat restored to abandoned 

ponds. 

2. Water table elevations 

throughout historic wetland area meet 

criteria for wetland hydrology. 

1. Observation, 

photos. 

2. Water table depth 

monitoring at 14 test sites 

within Upper CG. 

6 Water 

Outflow D B 1. Water out flow distributed through 

multiple channels and groundwater. 

1. Observation, 

photos 

7 Geomorphology D B 

1. Breached dams repaired and 

functional. 

2. Beavers present and actively 

maintaining dams. 

3. Soil profiles indicate hydric 

soil throughout historic wetland area. 

4. Boreas Creek channel is no 

longer enlarging or becoming further 

incised 

1. Observation, 

photos. 

2. Observation, 

photos, wildlife cameras. 

3. Soil profiles 

4. Channel surveys. 

8 Chemical 

Environment D B 

1. Restoration of the 

characteristic soil redox environment 

via reestablishment of the natural 

saturation regime. 

2. Maintain existing water 

quality 

1. Observation, 

photos, redox monitoring at 

test sites 

2. Evaluate ongoing 

WQ monitoring 

9 

Vegetation 

Structure 

and 

Complexity 

C B 

1. Wetland vegetation is present 

throughout historic wetland area. 

2. Vegetation composition and structure 

is similar to unimpacted reference 

condition. 

1. Observation, photos, 

sampling 

2. Vegetation plots at test sites, 

weed surveys, ongoing 

vegetation monitoring 
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Figure 65: An array of 14 test points were set up across the project area to track wetland conditions. 

Each point is equipped with a data-logging groundwater monitoring well, soil redox probes, and 

vegetation plots. The left photo shows results for the pre-project condition. The concentric circles at 

each test site indicate wetlands status based on hydrology (inner circle), vegetation (middle circle), and 

soils (outer circle). Green indicates the presence of a wetland indicator, red indicates the absence of a 

wetland indicator, and grey indicates the presence of relict hydric soils. The right photo shows postproject condition in 2014. Sites shaded green are positive for all three wetland indicators, those shaded 

in red are still lacking hydrology. The lines are delineations that reflect estimated wetland extent for 

2007 (pink) and 2009 (yellow). 

The reduced wetland condition prior to restoration is reflected in hydrology and soil redox 

data. Only one of the test points was positive for wetland hydrology and anaerobic soil 

chemistry in 2012, though relict hydric soil indicators were still present on all sites (indicating 

a recently dried wetland soil) and hydric vegetation prevalence indices were still positive on 

all but three sites (Table 10). This pattern is indicative of a recently dried wetland since it is 

common for hydric soil indicators to persist for years after a wetland is dried and for 

persistent species of hydric vegetation to "hang on" for several years after drying. The pattern 

also indicates an ideal wetland restoration scenario, since neither soils nor vegetation had 

been seriously impaired yet. 
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Post project hydrology, vegetation, and soil chemistry monitoring documented an immediate 

recovery of wetland conditions across most of the site (Figure 65 and Table 9. Pond and 

channel mapping indicates a recovery of most of these native aquatic features (Figure 64). 

Table 10: Three tables summarizing critical wetland parameters. Sites shaded green or blue had positive 

wetland indicators (green are terrestrial wetland and blue are ponds). Sites that are negative for wetland indicators 

are shown in red. The upper table shows results for hydrology monitoring. THD stands for Total Hydric Days 

and CHD stands for Consecutive Hydric days, where a hydric day is defined as one in which the mean static water 

table is less than 1.0 ft deep. Only one point had positive wetland hydrology prior to restoration in 2012, but 2 

years after treatment all but three points were positive. The lower left table shows similar results for soil chemistry, 

using reduction potential as an indicator of anaerobic conditions. The lower right table shows results for wetland 

vegetation monitoring. A prevalence index less of 3.00 or less is considered wetland vegetation. 
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While these results are 

encouraging, the initial positive 

response is more a direct effect 

of the mechanical treatments 

than an effect brought about by 

beaver. Wetland restoration 

success over the long term, 

however, depends on the 

recovery of a viable and active 

beaver population. At this 

point, the prognosis looks good. 

The one transplanted beaver 

was joined by several other 

"voluntary" beaver immigrants 

in 2013. In 2014, we observed

two separate beaver families on 

the site including several new 

kits (Figure 67). All but two of 

the dams in the project area 

were actively maintained by 

beavers through 2014. These 

results suggest that habitat 

conditions are once again 

suitable for beaver, and we are optimistic 

that they will remain here and continue 

to expand. 

In 2014, beavers had not yet constructed 

dams on the remaining incised segments 

of Boreas Creek, but signs of dam 

building were observed on the channel 

in spring of 2015. If beavers do not 

voluntarily build dams on this segment 

in 2015, we may consider constructing 

several additional BDAs to speed the 

recovery of the incised channel. 

Photos 

Photo documentation is perhaps the 

most powerful monitoring tool for 

showing the habitat conversion from dry 

upland to a functioning beaver-mediated 

wetland complex at the Cucumber Gulch Preserve. Taking photos from specific locations 

several times per year is a good way to track progress via time-lapse. Several time lapse 

photo series are provided here as an example (Figures 68-71). 

Figure 66: Condition of ponds and channels in 2014. Most of 

the native ponds and channels are now active

Figure 67: This pair of beaver kits was captured by a 

motion-trigger camera near lodge in the project area in 

2014, confirming suspicions that the beaver colonies on 

site were reproducing
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Figure 68: The left photo shows a repaired beaver dam and pond just after construction in 2012 with a 

single "spillway." Beaver dammed the spillway in 2013 and continued to raise the height of the dam in 

2014 (right photo). 

Figure 69: Sediment-filled ponds prior to treatment in 2012 (upper photo) and after they were treated 

and occupied by beavers in 2014 (lower photo). Ongoing maintenance will be required to capture 

incoming sediment at the head of the wetland to prevent ponds filling in the future.
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Figure 70: This series of photos shows a time lapse of one restored pond The small green "island" is a 

beaver lodge. Starting at the top, the photos are from (a) 2011 before the dam breached (note that the 

sediment plume extends to the lodge attaching it to the shoreline), (b) 2012 as the dam began breaching 

but before the channel incised, (c) 2013 after treatment but before beavers returned, and (d) 2014 after 

beavers returned. The returning beavers reoccupied the old lodge. 
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Figure 71: This series of photos shows a time lapse overview of a portion of the project area. Starting 

at the top, the photos are from (a) 2012 before the project, (b) 2013 after construction but before beavers 

arrived, (c) spring 2014 during runoff, and (d) summer 2014 after beavers significantly raised the height 

of dams.
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(9) Myers Creek, Washington Habitat Restoration Project

Okanogan Highlands Alliance (OHA), David Kliegman, Executive Director; Julie Ashmore, 

Conservation Coordinator

Location

Myers Creek, situated in Northeast Okanogan County in northern Washington State, near the 

Canadian Border. 

Restoration Goals

 Improve stream habitat

 Increase instream sediment retention to cause aggradation of the streambed over time

 Incrementally raise the water table through placement of LWD and BDAs that have the 

ability to adjust and adapt to dynamic stream conditions, and encourage natural 

habitat-forming processes

 Raise the local water table to facilitate the growth of native vegetation on the historical 

floodplain, providing resources to encourage beavers to recolonize the area and further 

modify and maintain the site

 Ultimately, re-establish a thriving, dispersing beaver colony onsite

Figure 72: Myers Creek restoration site showing locations of LWD and BDA placement

The Myers Creek Restoration site is owned by Kinross/Crown Resources, a gold mining 

company, and is a mitigation site for wetland impacts on Buckhorn Mountain. Traditionally, 
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this area supported freshwater emergent wetland and freshwater forested/shrub wetland.

Numerous Washington Department of Fish and Wildlife priority species have all been 

confirmed onsite, including rainbow trout, Columbia spotted frog and great blue heron. Prior 

to restoration activities, historic aerials indicate that LW was intentionally removed to 

facilitate grazing, which resulted in the loss of native riparian plant communities. Invasive 

Reed canarygrass began to dominate the riparian vegetation. Removal of beaver, combined 

with the loss of adequate food and construction resources, have substantially reduced the 

ability of the site to support dam-building beaver. 

Project implementation began in September of 2014, with the installation of the LW and BDAs 

to initiate habitat-forming processes. The BDAs were placed using three primary criteria: 1) 

locations downstream of areas producing high sediment loads from rapid bank erosion that 

would capture the most sediment; 2) where naturally occurring wood and debris piles had 

formed; and 3) where the structure would facilitate flooding onto a mid-level terrace that 

developed within the incision trench in certain parts of the reach. Large wood with root wads 

attached were placed at numerous locations within the channel, including BDAs (Figure 73), 

and BDAs were placed at five locations along the reach (Figure 72). The BDAs consisted of 

pilings sharpened at one end and driven four feet into the channel substrate with a pneumatic 

post driver. Almost all of the BDAs were channel spanning, with some extending up onto the 

bank (Figure 73). Only BDAs placed at naturally occurring debris piles were partially channel 

spanning (Figure 74). Pilings were woven with live red osier dogwood to encourage 

resprouting after placement. Some of the horizontal, woven red osier dogwood was planted 

directly into the side of the bank, especially at undercuts, to encourage growth and provide 

increased resistance of the bank (Figure 75). Other red osier clumps were planted vertically 

into the bank near the BDAs. Cobbles and grass were added to the upstream base of some of 

the structures to prevent scour, and brush mattresses were added to the downstream side of 

some BDAs to prevent development of a downstream scour pool, mimicking features found in 

natural beaver dams. 
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Figure 74: Partially channel spanning BDAs and LWD additions to a naturally occurring log and 

debris jam

Figure 73: BDA—Two pilings extending onto the bank with LWD placed through the structure
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Figure 75: Pilings woven with live red oiser dogwood, some of which was planted directly into the 

exposed bank to facilitate resprouting

Following installation, the BDAs immediately collected small wood and impounded water 

(see Figures 76 and 77). Two weeks after installation, water depth behind some of the 

structures had increased by up to 8 inches, completely submerging some of the LW. Six 

months later, some of the pilings were completely submerged, with the water level being 

much higher, and the wetted width continuing to increase. One of the BDAs, located in a 

narrow incision trench, developed a side cut from bank scour (Figure 78). This structure is still 

partially functioning in terms of water and sediment impoundment, and facilitating the 

widening of the incision trench at this location by directing the flow of water around the 

structure, increasing sheer stress on the bank and causing lateral migration of the channel.

This structure is not deemed a failure by the project team as it is adding complexity and 

habitat to the channel in the form of slow water habitat and development of an inset 

floodplain directly downstream. Before the next construction season, this structure will be 

reassessed, and adaptive management may be implemented to extend the post line and weave 

to fill the gap, wrapping it up the bank 5 to 10 feet. Additional BDAs may be installed 

downstream to help capture the sediment resources being released as the channel widens.

This project integrates adaptive management in order to facilitate natural habitat forming 

processes, has been deemed successful, and is being used as a pilot project for a larger 

restoration site upstream on Myers Creek, utilizing BDAs on a bigger scale. Monitoring will 

continue to evaluate the project and adaptive management will provide opportunities for 
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community involvement, and eventually allow for beaver recolonization. The site will be 

placed under a perpetual conservation easement. 

Figure 76: Before installation of a BDA and placement of LWD (see figure 82)

Figure 77: 12 days following installation of a BDA (same location as figure 81) and placement of LWD 

and other debris showing water pooling upstream
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Figure 78: Breach of BDA 1 showing water flowing around the structure, eroding the left bank. This 

BDA is still functioning as grade control through water impoundment upstream as well as facilitating 

the widening of the incision trench. Notice the development of an inset flood plain directly downstream 

along the right bank
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(10) Hansen Creek, Washington Floodplain Restoration Project

Skagit County and Upper Skagit Tribe, Lauren Rich

Location

Northern State Recreation Area Park on Hansen Creek, tributary to the Skagit River, in 

northwest Washington State.

Restoration Goals

 Reconnect 140 acres of alluvial fan, floodplain, and riverine wetlands to Hansen Creek

 Reduce flooding for downstream agricultural areas

 Increase complexity and habitat, especially for anadromous fish populations

 Increase native vegetation and reduce invasive vegetation (i.e. reed canary grass) 

below 15% total cover

 Increase amount of large wood on site

 Construct set-back levees to protect upland areas from flooding

 Increase ground and surface water levels

 Decrease stream temperatures

 Eliminate need for dredging through reductions in sediment loads

 Allow for beaver recolonization following construction completion

This project restored 140 acres and 17,000 lineal feet of stream, riparian, and floodplain habitat 

within the 726 acre recreation park. Most of the reed canary grass, which dominated the site 

(see Figure 79), was removed (Figure 80), side channels were excavated, 270 large wood 

structures were installed, and 90,500 trees, shrubs, live stakes, and wetland emergent plugs 

were planted. While the project design targeted restoration of salmon habitat, beavers were 

present in the vicinity prior to project implementation and the design was created with the 

assumption that they might return, colonize, and modify the site after construction was 

completed. The revegetation plan included a diverse array of native plant species including 

several species palatable to beavers. Though the project elements were designed specifically 

for salmon, the colonization by beavers is synergistically supporting salmon habitat. 

This site is well-suited to accommodate beaver colonization and modification due to its very 

large size and owner (Skagit County) that desire a return to natural floodplain function.

Adjacent infrastructure and private land is protected from flooding by set-back levees and 

dikes, allowing for the construction and expansion of beaver dams and their subsequent 
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impoundment of water. Construction on the site was largely completed by 2009. In August of 

2013, beavers started constructing dams and a lodge in the riverine wetland habitat, which 

they have since greatly expanded (>600 lineal feet of dams providing 11 acres of summer lowflow inundated area)(Figure 81). This beaver activity has increased summer low flow wetted 

area and increased pool habitat in the wetland area, improving rearing habitat for coho 

salmon and steelhead trout and improving stream/groundwater interactions. This project also 

provides an educational opportunity because the park land allows numerous visitors easy 

access due to the construction of an additional 1.5 miles of trail traversing through the 

restoration site. 

Figure 79: Photo taken on 06/30/2009 of the restoration site pre-project initiation showing 

invasive reed canarygrass as the dominant vegetation present

Figure 80: Photo of the restoration site during construction after removal of invasive reed 

canarygrass
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Figure 81: Photo taken on 06/04/2013 of the site four years following completion of construction. 

Beavers built a lodge in the restored wetland and numerous dams, which they continue to add to and 

maintain

Beaver lodge location
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(11) Beaver Reintroduction on Private Property, New Mexico 

Cathryn Wild, Executive Director/Science and Stewardship Director, Seventh Generation 

Institute

cwild@seventh-generation.org

505 216 1150

PO Box 31698 

Santa Fe NM 87594

www.seventh-generation.org

Project Partners

The landowners, USFWS Partners for Fish and Wildlife , Integral Ecology, The Biophilia 

Foundation, Patagonia, Inc., The Norcross Wildlife Foundation, New Mexico Department of 

Game and Fish, ESRI Conservation Program, Individual donors and volunteers

Location

Eastern New Mexico, Private Ranch, on a perennial, but spatially intermittent stream. 

Restoration Goals and Objectives

Improve riparian function and resilience (restoration [repairing the past] and climate change 

adaptation [preparing for the future]: specifically,

 downcutting will not exceed current levels

 existing incision and the water table will be elevated at least until the stream can 

reconnect to the original floodplain and over bank flooding occurs

 Double the width of riparian area vegetation, double the quantity and complexity 

(multi-storied) of riparian and buffer zone vegetation , use the project as a model 

project to demonstrate the effectiveness of beaver, specifically, the compatibility of 

beavers and ranching

 Double the productivity of forage within the area

 increase the amount of water held on the site in the stream system

 communicate successes/results to other ranchers.

 hold workshops, provide other outreach events, publish, and present

Site Description

The stream is located in eastern New Mexico on a very large, working family ranch. 

Surrounded by steep banks with rocky substrate, the stream is located in a high, arid desert 

region with short grass prairie habitat. The water regime is highly variable, fluctuating 
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between drought and severe flash flooding due to summer monsoons. Flow is perennial with 

spatially intermittent reaches. In the early 1900’s, the stream was straightened by the previous 

generation of owners. Following intense rainfall and flooding events in the 1940’s, the stream 

started actively incising. Currently, incision in some reaches is up to 25 feet resulting in very 

high stream power during high flow events, degraded riparian zones, and disconnection from 

the floodplains with no overbank flooding in most reaches. Large wood or any other 

impoundments are lacking in the stream channel. No beavers have been present on this stretch 

of river or the surrounding areas up and downstream for decades. The site has been fairly

heavily grazed in the past. The current generation of owners, which is deeply committed to 

restoring land and stream health, is utilizing holistic grazing practices by controlling the 

timing and intensity of grazing of certain areas with exclusion fencing. Riparian vegetation is 

primarily cottonwood and sedges with lesser amounts of willow. Salt cedar and Russian olive 

had been removed prior to initiation of project activities. 

Seventh-Generation is a non-profit organization based out of Santa Fe, New Mexico. They are 

using adaptive management techniques to reintroduce beaver to this stretch of stream in 

eastern New Mexico located on a private ranch. The project started 3-4 years ago and has 

involved terrific collaboration with the ranch family from the outset including huge amounts 

of labor, ideas, and funds. Beaver dam analogues were placed in several places to encourage 

upstream pooling and ponding, and sediment deposition. The BDAs consist of reused juniper 

fence posts, driven into the streambed to resist high-flow events that would typically blow out

natural beaver dams. Cut cottonwood saplings were placed in between the posts parallel to 

the stream flow with cut stems facing upstream, and additional cottonwood saplings were 

interwoven between the posts perpendicular to stream flow and tamped down to tighten up 

all the branches. This design was copied from the first edition of the Salmonid Habitat 

Restoration written in 1991 by Gary Flosi and Forrest Reynolds. Due to severe flash floods, 

downstream scour behind the beaver dams was a concern. The saplings placed parallel to the 

flow with cut ends upstream and small branching down steam directly on the stream bed was 

intended to act as a “brushwood mattress” that would be more resilient to scour underneath 

the dam (Figure 82). This mimics features found in natural beaver dams that reduce the 

development of downstream scour pools. Since installation, the starter dams have survived 

major flooding events and accumulated substantial amounts of sediment. 
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Figure 82: BDA interwoven with cottonwood branches parallel and perpendicular to the stream flow. 

The perpendicular, downstream (left to right) branches are placed to limit the development of a 

downstream scour pool during high-flow events, which could compromise the integrity of the 

structure. Photo courtesy of Seventh-Generation Institute.

Four beavers were translocated and reintroduced to the stream (Figure 83), two of which were 

fitted with tail mounted radio transmitters by a veterinarian (protocol followed Arjo et al. 

2008). Temporary lodges were provided at one release site (Figure 84) to provide cover after 

release, which can reduce stress, the risk of predation and the probability of beaver leaving the 

release site. The four beavers, two males and two females, one pair of which were siblings, 

were released in a site with an existing pond, robust cottonwood and willow trees along the 

shoreline, and installed BDAs. All but one beaver (a female) left the release area, presumably 

moving downstream. The female was using a bank burrow at the release site. One male has 

moved downstream to an area with much less standing water and riparian vegetation. He 

unsuccessfully attempted to build a dam while living in a bank burrow. All radio transmitters

failed, but beaver are still being tracked by sign. Risk of predation by mountain lion and 

coyote in the area is very high and, unfortunately, only one beaver is currently believed to 

have survived. To date, there has been no attempt by the reintroduced beaver to add or 

maintain any of the faux dams. Food supplementation was provided during the winter 

months and consisted of cottonwood saplings placed on the shoreline. Beaver readily took 

advantage of this resource presumably adding to a food cache in the pond. Exclusion fencing 

was placed around large cottonwoods to prevent herbivory by beaver ensuring that a 

significant amount of overstory remained for wildlife.
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Figure 83: Beaver release site with deep-water habitat provided by placement of BDA (out of photo). 

Notice the pile of cottonwood branches placed on the bank to provide food resources to the 

reintroduced beavers and encourage them to remain at the release site. Photo courtesy of SeventhGeneration Institute.

Figure 84: Release of beaver into a temporary lodge placed on the bank of the stream. Photo courtesy 

of The Seventh-Generation Institute.
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This is a great example of utilizing several techniques offered in this guidebook: utilization of 

BDAs (called faux dams in this project), temporary lodges during reintroductions, exclusion 

fencing to protect vegetation from herbivory of both beaver and ungulates, and the 

reintroduction of beaver. Highly incised streams often prevent beaver from being able to build 

long-lasting dams (at least two years) or provide enough resources in the form of developed 

riparian and/or floodplain plant communities. Using BDAs to create ponds and deep water 

habitat, and initiate natural habitat-forming processes may increase the probability that the 

reintroduced beaver will stay at the release site, survive, and eventually start building and 

maintaining dams. 

Lessons Learned to Date

This project truly illustrates the contribution of luck and timing in restoration outcomes, at 

least as much as specific methods. This project encountered numerous challenges, including a 

drought of the most severe category, “exceptional,” almost immediately after initiation of the 

project activities. This was punctuated with record breaking convective precipitation that

produced severe flash flooding. This combination reduced the statewide supply of beavers 

available to translocate, reduced food supplies for beaver, increased predation pressure, and

forced the land owners to divert time to unexpected tasks. In addition, project partners 

encountered significant health and family issues during this project, including the death of 

one of the land owners. This too, profoundly affected the project activities.

These climate conditions are a repeat of the historic conditions found in this area during the 

Dust Bowl, or alternatively may be viewed as conditions expected under an altered climate 

several decades hence. While the project was designed to help protect against altered climate, 

arrival of such severe conditions decades earlier than expected has not allowed the project to 

gain a foot hold. Although the drought has eased slightly, the area remains in drought after 

approximately 5 years. Statewide beaver populations are starting to recover, as is vegetation. 

Conditions over the next few years will continue to influence outcomes. This illustrates how 

narrow the resilience building window of time is in the Southwest.

This project also illustrates some of the obstacles found in restoration work, where textbookbased project selection criteria never quite jive with reality. Not all land, water flows, or other 

conditions are under control of the partners. Pros and cons of a project must be carefully 

weighed - is this project worth investing time, effort and funds?

Project partners knew that this project would be very challenging, even before the severe 

drought conditions arrived. A few specific factors that contributed to the challenge were: 1) 

the remoteness of the site, which made labor and materials more scarce and expensive; 2) lack 

of control over conditions of the upper watershed, which is also private land, but believed to 

be in poor condition, resulting in large runoff events; 3) location of the project on private land, 

with a limited supply of funders willing to fund projects that benefit private lands; 4) high 

potential predation rates on translocated beaver, from a very healthy population of coyotes, 

mountain lions and others. In sum, none of the project partners were clear that the project 

would be a “success” if success were defined as immediate or short term completion of all 

activities and results.
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In contrast, the large scale of the site, support of the land owners and specifically, their 

willingness to experiment with various techniques, enabled us to push the “beaver-assisted 

restoration envelope” on this project and try to discover if beaver and BDAs could, over 

longer periods of time and under extreme conditions, still restore important processes to this 

stream system and build resilience. The decision was made to try, and at a minimum, learn 

some lessons. 

Translocation techniques, tree wrapping, riparian fencing, grazing management changes, 

supplemental feeding and monitoring have all worked well. Attachment of radio transmitters 

was successful to the extent that no animals were ill or lost in the attachment procedure. The 

failure of the radio transmitters to perform over long periods of time in the field was not 

unexpected, but still a disappointment.

All project partners were very pleased with the performance of the initial set of BDAs. They 

withstood very large flows – estimated at 50-75 feet wide, 6-8 feet high - without scouring.

However, the intensity of the flash flooding meant that the BDAs filled with sediment much 

faster than anticipated – one flash flood completely filled the dams with sediment. This is a 

positive outcome overall, in the sense that they served the restoration goals. But the beaver 

never had a chance to use them. Ideally, crews would have rapidly built additional BDAs. But 

at this point, funding was exhausted, “crews” were not available due to labor shortages in the 

area, and several project partners were coping with the family and health issues mentioned 

previously. Additional project activities have had to be postponed. In sum, the jury is still out 

on the eventual restoration results of this project. Unquestionably, the goal of learning has 

been and will continue to be met. 

Next Steps

Drought and other conditions are being monitored in hopes of an improved restoration 

window. Next steps in the project will be to significantly expand the project area and the scope 

of all project activities, with the expectation that an expanded scope will push the project area 

over a tipping point and initiate a new positive feedback cycle. 
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Section III – Additional Information 

and Resources

Beaver Resources

The following websites provided useful information regarding beaver, with the first two 

sources mentioned being particularly notable for their wealth of information:

 Worth a Dam

http://www.MartinezBeavers.org

Contact: Heidi Perryman

 Cows and Fish

Beaver - Our Watershed Partner by Lorne Fitch, 2016 

http://cowsandfish.org/publications/documents/BeaverOurWatershedPartnerWEB.pdf

Contact: Norine Ambrose

 Beavers: Wetlands and Wildlife

http://www.beaversww.org

Contact: Sharon Brown

 Beaver Solutions

http://www.beaversolutions.com

Contact: Mike Callahan

 Animal Protection of New Mexico

http://www.apnm.org/campaigns/beavers/

 Washington Department of Fish and Wildlife 2012 Stream Habitat 

Restoration Guidelines and general information on living with beaver

http://wdfw.wa.gov/publications/01374/

http://wdfw.wa.gov/living/beavers.html

 The Occidental Arts and Ecology Center WATER Institute

http://www.oaec.org/publications/beaver-in-california

http://www.oaec.org/beaver

Contact: Kate Lundquist and Brock Dolman
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 The Seventh Generation Institute

http://www.seventh-generation.org/

Contact: Cathryn Wild

 King County

http://www.kingcounty.gov/environment/animalsAndPlants/beavers.aspx

 The Beaver Solution

http://www.landscouncil.org/beaversolution/

Contact: Joe Cannon

 The Grand Canyon Trust

http://www.grandcanyontrust.org/

Contact: Mary O’Brien

Many others deserve recognition as well, but the listed organizations and websites are good 

starting places that contain numerous links to myriad beaver-related resources, news, trivia, 

entertainment, people, and information.

For those who would like to read some classic books on the beaver, we can recommend 

several: 

 The American Beaver and His Works, by Lewis Henry Morgan (1868)

 In Beaver World, by Enos Mills (1913) 

 Three Against the Wilderness, by Eric Collier (1959)

 Beaversprite: My Years Building an Animal Sanctuary, by Dorothy Richards (1984)

 Lily Pond: Four Years With A Family of Beavers, by Hope Ryden (1989) 

 The Beaver: Natural History of a Wetlands Engineer, by Dietland Müller-Schwarze and 

Lixing Sun (2003; updated 2011)
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Acronyms and Abbreviations

BDAs beaver dam analogues

BLM Bureau of Land Management

BMPs best management practices

DBH diameter at breast height

ESA Endangered Species Act 

GIS geographical information system

GNIS Geographic Names Information Systems

ID identification number

ITIS Integrated Taxonomic Information System 

IUCN International Union for the Conservation of Nature 

NEPA National Environmental Policy Act

NOAA National Oceanic and Atmospheric Administration

ODFW Oregon Department of Fish and Wildlife

PIT Passive Integrated Transponder

PLWW post lines with wicker weaves

PPE personal protective equipment

PVC polyvinyl chloride

RCW Revised Code of Washington 

USFS U.S. Forest Service 

USFWS U.S. Fish and Wildlife Service

μg/l micrograms per liter
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Appendix A. Plant Species Eaten by North 

American Beaver

Species of Woody, Herbaceous, and Common Foods Known to Be Eaten by Beaver

Woody Species

Common Name Species Location Source

loblolly pine Pinus taeda SE USA 1

sweet gum Liquidambar styraciflua SE USA 1

southern sweetbay Magnolia virginiana SE USA 1

spruce pine Pinus glabra SE USA 1

willow Salix species NE USA 1

maple Acer species NE USA 1

oak Quercus species NE USA 1

alder Alnus species NE USA 1

gray birch Betula populifolia NE USA 1

white pine Pinus strobus NE USA 1

quaking aspen Populus tremuloides NE USA 1

willow Salix species Western USA 1

cottonwood Populous Species Western USA 1

trembling aspen Populus tremuloides Western USA 1

ash Fraxinus Species Western USA 1

choke cherry Prunus virginiana Western USA 1

bog birch betula glandulosa Western USA 1

mountain alder Alnus incana Western USA 1
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chaparral Various species Western USA 1

currants Ribes species Western USA 1

silverberry Elaeagnus commatata Western USA 1

russet buffaloberry Shepherdia Canadensis Western USA 1

lodgepole pine Pinus contorta Western USA 1

white fir Abies concolor Western USA 1

blue spruce Pinus pungens Western USA 1

black hawthorn Crataegus douglasii Western USA 1

willow Salix species New York 2

apple Pyrus malus New York 2

juneberry or shadbush Amelanchier species New York 2

black cherry Prunus serotina New York 2

quaking aspen Populus tremuloides New York 2

American beech Fagus grandifolia New York 2

musclewood Carpinus caroliniana New York 2

hop hornbeam Ostrya virginiana New York 2

sugar maple Acer saccharum New York 2

red pine Pinus resinosa New York 2

Eastern hemlock Tsuga canadensis New York 2

yellow birch Betula alleghaniensis New York 2

Norway spruce Picea abies New York 2

red maple Pinus sylvestris New York 2

ash Fraxinus Species New York 2

maple Acer species New York 2

witch-hazel Hamamelis virginiana New York 2
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hawthorn Crataegus species New York 2

white pine Pinus strobus New York 2

willow Salix species Oregon 3

red alder Alnus rubrus Oregon 3

vine maple Acer circinatum Oregon 3

cottonwood Populus species Oregon 3

salmon berry Rubus spectabilis Oregon 3

big-leaf maple Acer macrophylum Oregon 3

sitka spruce Picea sitchensis Oregon 3

western hemlock Tsuga heterophylla Oregon 3

elderberry Sambucus species Oregon 3

thimbleberry Rubus parviflorus Oregon 3

salal Gaultheria shallon Oregon 3

western red cedar Thuja plicata Oregon 3

Douglas fir Pseudotsuga menziesii Oregon 3

willow Salix species NW Terr., CA 4

poplar Polulus balsamifera NW Terr., CA 4

alder Alnus crispa NW Terr., CA 4

white Oak Quercus alba Massachusetts 5

northern red oak Quercus rubra Massachusetts 5

black oak Quercus velutina Massachusetts 5

grey birch Betula populifolia Massachusetts 5

yellow birch Betula lutea Massachusetts 5

eastern white pine Pinus strobus Massachusetts 5

red pine Pinus resinosa Massachusetts 5
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red maple Acer rubrum Massachusetts 5

sugar maple Acer saccharum Massachusetts 5

whitch hazel Hamamelis virginiana Massachusetts 5

iron wood Carpinus caroliniana Massachusetts 5

black cherry Prunus serotina Massachusetts 5

eastern hemlock Tsuga canadensis Massachusetts 5

holly Ilex species Massachusetts 5

blueberry Vaccinium corymbosum Massachusetts 5

white ash Fraxinus americana Massachusetts 5

hawthorn Crataegus Species Massachusetts 5

hornbeam Ostrya virginiana Massachusetts 5

american chestnut Castanea dentata Massachusetts 5

spruce Picea species Massachusetts 5

red maple Acer rubrum Michigan 6

sugar maple Acer saccharum Michigan 6

mountain maple Acer spicatum Michigan 6

speckled Alder Alnus rugosa Michigan 6

yellow birch Betula alleghaniensis Michigan 6

paper birch Betula papyrifera Michigan 6

red osier dogwood Cornus stolonifera Michigan 6

beaked hazel Corylus cornuta Michigan 6

american mountain 

ash Sorbus americana Michigan 6

eastern cottonwood Populus deltoides Texas 7

bur oak Quercus macrocarpa Texas 7
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mulberry Moru Alba Texas 7

mexican buckeye Ungnadia speciosa Texas 7

buttonbush Cephalanthus occidentalis Texas 7

dogwood Cornus species Texas 7

texas ash Fraxinus texensis Texas 7

red buckeye Aesculus pavia Texas 7

bald cypress Taxodium distichum Texas 7

boxelder Acer negundo Texas 7

hackberry Celtis species Texas 7

pecan Carya illinoinensis Texas 7

cedar elm Ulmus crassifolia Texas 7

chinaberry melia azedarach Texas 7

privet Ligustrum vulgare Texas 7

black willow Salix nigra Texas 7

sycamore Plantanus occidentalis Texas 7

american elm Ulmus americana Texas 7

Herbaceous Species

Common Name Species Location Source

rice cutgrass Leersia oryzoides SE USA 8

golden club Orontium aquaticum SE USA 8

switchgrass Arundinaria tecta SE USA 8

poison ivy Toxicodendron radicans SE USA 8

pondweed Potamogeton species SE USA 8

grasses Gramineae NE USA 8
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queen-of-the-meadow Filipendula ulmaria NE USA 8

evergreen Christmas 

fern

Polystichum 

acrostichoides NE USA 8

field fern ? NE USA 8

sedge Carex NE USA 8

waterweed Elodea species NE USA 8

white water lily Nymphaea adorata NE USA 8

yellow pond lilly Nuphar advena NE USA 8

water-shield Brasenia schreberi NE USA 8

water arum calla palustris NE USA 8

sedges Carex Species Western USA 8

grasses Graminae Western USA 8

mountain pond lilies Nuphar polysepalum Western USA 8

horsetail Equisetum species Western USA 8

cattail Typha species Western USA 8

Bur-reed Sparganium americanum Georgia 9

lizard's tail Saururus cemuus Georgia 9

marsh seedbox Ludwigia palustris Georgia 9

smartweed Polygonum densiflorum Georgia 9

milfoil Myriophyllum aquaticum Georgia 9

water lily Nuphar variegatum NW Terr., CA 4
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Cultivated or manufactured Foods

Common Name Species Location Source

commercial rodent 

pellets n/a Washington 10

apples Malus species Washington 10

alfalfa Medicago sativa Washington 10

acorns Quercus species NE USA 1

corn Zea mays New York 2

soybean Glycine max SE USA 8

Sources: 

1 = Novak (1999)

2 = Müller-Schwarze (2011)

3 = Bruner (1989)

4 = Aleksiuk (1970)

5 = Jenkins (1979)

6 = Belovsky (1984)

7 = Baccus et al. (2007)

8 = Novak (1999)

9 = Parker et al. 2007

10 = Kent Woodruff, Methow Valley Beaver Project, personal 

communication

For more information on beaver eating habits see “What do Beaver Eat?”, a literature review 

prepared for the Grand Canyon Trust (Henker 2009).
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Appendix B. Subspecies of C. canadensis 

Considered “Invalid” by ITIS

All Subspecies of the North American Beaver are Recognized as "Invalid" by 

the Integrated Taxonomic Information System (ITIS.gov)

Castor canadensis Kuhl, 1820 – valid – American Beaver 

Castor canadensis acadicus Bailey and Doutt, 1942 – invalid 

Castor canadensis baileyi Nelson, 1927 – invalid 

Castor canadensis belugae Taylor, 1916 – invalid 

Castor canadensis caecator Bangs, 1913 – invalid 

Castor canadensis canadensis Kuhl, 1820 – invalid 

Castor canadensis carolinensis Rhoads, 1898 – invalid 

Castor canadensis concisor Warren and Hall, 1939 – invalid 

Castor canadensis duchesnei Durrant and Crane, 1948 – invalid 

Castor canadensis frondator Mearns, 1897 – invalid 

Castor canadensis idoneus Jewett and Hall, 1940 – invalid 

Castor canadensis labradorensis Bailey and Doutt, 1942 – invalid 

Castor canadensis leucodontus Gray, 1869 – invalid 

Castor canadensis mexicanus Bailey, 1913 – invalid 

Castor canadensis michiganensis Bailey, 1913 – invalid 

Castor canadensis missouriensis Bailey, 1919 – invalid 

Castor canadensis pallidus Durrant and Crane, 1948 – invalid 

Castor canadensis phaeus Heller, 1909 – invalid 

Castor canadensis repentinus Goldman, 1932 – invalid 

Castor canadensis rostralis Durrant and Crane, 1948 – invalid 

Castor canadensis sagittatus Benson, 1933 – invalid 

Castor canadensis taylori Davis, 1939 – invalid 

Castor canadensis texensis Bailey, 1905 – invalid

Castor subauratus Taylor, 1912 – invalid

Castor subauratus shastensis Taylor, 1916 - invalid