Technical Manual for 

Dam Owners 

Impacts of Animals on Earthen Dams

FEMA 473 / September 2005
Twenty-five states across the U.S. can write headlines of dam failure caused by nuisance 

wildlife intrusions, and many dam owners find the struggle to adequately manage nuisance 

wildlife at their dams a never-ending story. The Federal Emergency Management Agency 

(FEMA) has funded the development of this manual with the understanding that safe dam 

operation includes comprehensive, state-of-practice guidance on timely inspection and observation of wildlife damages, accurate wildlife identification and mitigation, and appropriate 

dam design, repair, and preventive measures. It is hoped that the information and methods 

contained in this manual will compose the core of dam management routines practiced by 

dam specialists across the country. Armed with education and diligence, dam specialists can 

prevent animal intrusion dam failure from becoming headline news. 
Technical Manual for 

Dam Owners

Impacts of Animals on Earthen Dams

i

Table of Contents

1.0 Introduction and Purpose of Manual ...........................................................................1

1.1 Background ............................................................................................................1

1.2 Target Audience, Purpose, and Application of This Manual .....................................2

1.3 Technical Resources Cited .......................................................................................3

2.0 Impacts of Wildlife on Earthen Dams .......................................................................4

2.1 Background ............................................................................................................4

2.2 Hydraulic Alteration ................................................................................................5

2.3 Structural Integrity Losses ......................................................................................6

2.4 Surface Erosion .......................................................................................................6

3.0 Dam Inspection From Two Perspectives: Engineering Function and Biological 

Potential .....................................................................................................................8

3.1 Wildlife and the Earthen Dam ...............................................................................8

3.2 Two-Perspective Dam Inspection Methodology .....................................................9

3.2.1 Zone 1: Upstream Slope Area .......................................................................9

3.2.2 Zone 2: Dam Crest Area ............................................................................ 10

3.2.3 Zone 3: Upper Downstream Slope Area .................................................... 12

3.2.4 Zone 4: Lower Downstream Slope Area ..................................................... 13

3.2.5 Zone 5: Downstream Toe Area ................................................................... 13

3.2.6 Zone 6: Spillway, Outlets, and General Areas ............................................ 14

4.0 Overview and Identification of Nuisance Wildlife ................................................. 15

4.1 The Importance of Accurate Wildlife Identification ............................................. 15

4.2 Identifying Nuisance Wildlife ............................................................................ 17

4.2.1 Muskrat Overview .................................................................................... 17

4.2.2 Beaver Overview ....................................................................................... 19

4.2.3 Mountain Beaver Overview ...................................................................... 22

4.2.4 Groundhog Overview .............................................................................. 24

4.2.5 Pocket Gopher Overview ......................................................................... 26

4.2.6 North American Badger Overview ............................................................ 29

4.2.7 Nutria Overview ....................................................................................... 31

4.2.8 Prairie Dog Overview ............................................................................... 33

4.2.9 Ground Squirrel Overview ....................................................................... 35

4.2.10 Armadillo Overview ............................................................................... 37

4.2.11 Livestock Overview ................................................................................ 39

4.2.12 Crayfish Overview .................................................................................. 41

4.2.13 Coyote Overview .................................................................................... 42

4.2.14 Moles and Voles Overview ...................................................................... 44

4.2.15 River Otter Overview ............................................................................. 47

4.2.16 Gopher Tortoise Overview ...................................................................... 48

4.2.17 Red Fox and Gray Fox Overview ............................................................ 50

4.2.18 Canada Goose Overview ......................................................................... 52

4.2.19 American Alligator Overview .................................................................. 54

4.2.20 Ants Overview ........................................................................................ 55

5.0 Dam Repair and Intrusion Prevention Through Design ........................................ 57

5.1 Conformity to the Clean Water Act of 1972 ......................................................... 57

5.2 The Role of Vegetation Management ................................................................... 58

5.3 Burrow Repair Procedures .................................................................................. 58

5.3.1 Restoration Measures ................................................................................ 58

5.3.2 Preventive Measures ................................................................................. 59
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5.4 Dam Repair Zones ............................................................................................... 59

5.4.1 Dam Repair Zone 1 ................................................................................. 60

5.4.2 Dam Repair Zone 2 .................................................................................. 62

5.4.3 Dam Repair Zone 3 .................................................................................. 62

5.4.4 Dam Repair Zone 4 .................................................................................. 63

5.4.5 Dam Repair Zone 5 .................................................................................. 63

5.5 Professional Dam Safety Review .......................................................................... 64

5.6 Sequenced Repair Program ................................................................................. 64

5.7 Mitigation Through Design ................................................................................ 64

5.7.1 Muskrat ................................................................................................... 64

5.7.2 Beaver ...................................................................................................... 66

5.7.3 Mountain Beaver ...................................................................................... 68

5.7.4 Groundhog .............................................................................................. 68

5.7.5 Pocket Gopher ......................................................................................... 68

5.7.6 North American Badger ............................................................................ 68

5.7.7 Nutria ....................................................................................................... 68

5.7.8 Prairie Dog .............................................................................................. 68

5.7.9 Ground Squirrel ....................................................................................... 68

5.7.10 Armadillo .............................................................................................. 69

5.7.11 Livestock ................................................................................................ 69

5.7.12 Crayfish .................................................................................................. 69

5.7.13 Coyote .................................................................................................... 69

5.7.14 Mole and Vole ......................................................................................... 69

5.7.15 River Otter ............................................................................................. 69

5.7.16 Gopher Tortoise ..................................................................................... 70

5.7.17 Red and Gray Fox ................................................................................... 70

5.7.18 Canada Goose ......................................................................................... 70

5.7.19 American Alligator ................................................................................. 70

5.7.20 Ants ........................................................................................................ 70

5.8 Monitoring ........................................................................................................ 70

6.0 Mitigating Damaging Wildlife ................................................................................ 71

6.1 Compliance with State and Federal Regulations .................................................. 71

6.1.1 Conformity to Federal Regulations ........................................................... 71

6.1.2 Conformity to State Regulations ............................................................... 72

6.2 Muskrat Management Methods .......................................................................... 73

6.2.1 Muskrat Control Through Habitat Modification ....................................... 73

6.2.2 Muskrat Control Through Trapping ........................................................... 73

6.2.3 Muskrat Control Through Fumigants ....................................................... 75

6.2.4 Muskrat Control Through Toxicants .......................................................... 75

6.2.5 Muskrat Control Though Frightening ....................................................... 76

6.2.6 Muskrat Control Through Repellents ........................................................ 76

6.2.7 Muskrat Control Through Shooting ......................................................... 76

6.3 Beaver Management Methods .............................................................................. 76

6.3.1 Beaver Control Through Habitat Modification .......................................... 76

6.3.2 Beaver Control Through Trapping ............................................................. 76

6.3.3 Beaver Control Through Fumigants .......................................................... 77

6.3.4 Beaver Control Through Toxicants ............................................................ 77

6.3.5 Beaver Control Through Frightening ........................................................ 77

6.3.6 Beaver Control Through Repellents .......................................................... 77

6.3.7 Beaver Control Through Shooting ............................................................. 77
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6.4 Mountain Beaver Management Methods ............................................................. 77

6.4.1 Mountain Beaver Control Through Habitat Modification ......................... 77

6.4.2 Mountain Beaver Control Through Trapping ............................................. 77

6.4.3 Mountain Beaver Control Through Fumigants ......................................... 77

6.4.4 Mountain Beaver Control Through Toxicants ............................................ 78

6.4.5 Mountain Beaver Control Through Frightening ...................................... 78

6.4.6 Mountain Beaver Control Through Repellents ......................................... 78

6.4.7 Mountain Beaver Control Through Shooting ........................................... 78

6.5 Groundhog Management Methods ...................................................................... 78

6.5.1 Groundhog Control Through Habitat Modification .................................. 78

6.5.2 Groundhog Control Through Trapping .................................................... 78

6.5.3 Groundhog Control Through Fumigants .................................................. 78

6.5.4 Groundhog Control Through Toxicants .................................................... 78

6.5.5 Groundhog Control Though Frightening ................................................. 78

6.5.6 Groundhog Control Through Repellents ................................................ 79

6.5.7 Groundhog Control Through Shooting .................................................. 79

6.6 Pocket Gopher Management Methods ................................................................. 79

6.6.1 Pocket Gopher Control Through Habitat Modification ............................. 79

6.6.2 Pocket Gopher Control Through Trapping ................................................ 79

6.6.3 Pocket Gopher Control Through Fumigants ............................................. 80

6.6.4 Pocket Gopher Control Through Toxicants ............................................. 80

6.6.5 Pocket Gopher Control Through Frightening ............................................ 81

6.6.6 Pocket Gopher Control Through Repellents ............................................ 81

6.6.7 Pocket Gopher Control Through Shooting ............................................. 82

6.7 North American Badger Management Methods ................................................... 82

6.7.1 North American Badger Control Through Habitat Modification ............... 82

6.7.2 North American Badger Control Through Trapping ................................. 82

6.7.3 North American Badger Control Through Fumigants ............................... 82

6.7.4 North American Badger Control Through Toxicants ................................. 82

6.7.5 North American Badger Control Through Frightening ............................ 82

6.7.6 North American Badger Control Through Repellents ............................... 82

6.7.7 North American Badger Control Through Shooting ................................. 82

6.8 Nutria Management Methods .............................................................................. 82

6.8.1 Nutria Control Through Habitat Modification .......................................... 82

6.8.2 Nutria Control Through Trapping ............................................................ 83

6.8.3 Nutria Control Through Fumigants .......................................................... 83

6.8.4 Nutria Control Through Toxicants ............................................................ 83

6.8.5 Nutria Control Through Frightening ....................................................... 83

6.8.6 Nutria Control Through Repellents .......................................................... 83

6.8.7 Nutria Control Through Shooting ............................................................ 84

6.9 Prairie Dog Management Methods ...................................................................... 84

6.9.1 Prairie Dog Control Through Habitat Modification .................................. 84

6.9.2 Prairie Dog Control Through Trapping ..................................................... 84

6.9.3 Prairie Dog Control Through Fumigants .................................................. 84

6.9.4 Prairie Dog Control Through Toxicants ..................................................... 85

6.9.5 Prairie Dog Control Through Frightening ................................................. 85

6.9.6 Prairie Dog Control Though Repellents .................................................... 85

6.9.7 Prairie Dog Control Through Shooting .................................................... 85

6.10 Ground Squirrel Management Methods ............................................................. 85
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6.10.1 Ground Squirrel Control Through Habitat Modification .........................86

6.10.2 Ground Squirrel Control Through Trapping ............................................86

6.10.3 Ground Squirrel Control Through Fumigants .........................................86

6.10.4 Ground Squirrel Control Through Toxicants ...........................................86

6.10.5 Ground Squirrel Control Through Frightening .......................................87

6.10.6 Ground Squirrel Control Through Repellents .........................................87

6.10.7 Ground Squirrel Control Through Shooting ...........................................87

6.11 Armadillo Management Methods ......................................................................87

6.11.1 Armadillo Control Through Habitat Modification ...................................87

6.11.2 Armadillo Control Through Trapping ......................................................87

6.11.3 Armadillo Control Through Fumigants ...................................................88

6.11.4 Armadillo Control Through Toxicants ....................................................88

6.11.5 Armadillo Control Through Frightening ..................................................88

6.11.6 Armadillo Control Through Repellents ...................................................88

6.11.7 Armadillo Control Through Shooting ....................................................88

6.12 Livestock (Cow, Sheep, Horse, Pig, and Wild Pig) Management Methods ..........88

6.12.1 Livestock Control Through Habitat Modification ....................................88

6.12.2 Livestock Control Through Trapping .......................................................88

6.12.3 Livestock Control Through Fumigants ....................................................89

6.12.4 Livestock Control Through Toxicants ......................................................89

6.12.5 Livestock Control Through Frightening ..................................................89

6.12.6 Livestock Control Through Repellents ....................................................89

6.12.7 Livestock Control Through Shooting ......................................................89

6.13 Crayfish Management Methods .........................................................................89

6.13.1 Crayfish Control Through Habitat Modification ......................................89

6.13.2 Crayfish Control Through Trapping ........................................................89

6.13.3 Crayfish Control Through Fumigants ......................................................89

6.13.4 Crayfish Control Through Toxicants .........................................................89

6.13.5 Crayfish Control Through Frightening .....................................................89

6.13.6 Crayfish Control Through Repellents .......................................................89

6.13.7 Crayfish Control Through Shooting .........................................................89

6.14 Coyote Management Methods ...........................................................................89

6.14.1 Coyote Control Through Habitat Modification .......................................89

6.14.2 Coyote Control Through Trapping ..........................................................89

6.14.3 Coyote Control Through Fumigants ........................................................90

6.14.4 Coyote Control Through Toxicants ..........................................................90

6.14.5 Coyote Control Through Frightening ......................................................90

6.14.6 Coyote Control Through Repellents .......................................................90

6.14.7 Coyote Control Through Shooting ..........................................................90

6.15 Mole and Vole Management Methods ...............................................................90

6.15.1 Mole and Vole Control Through Habitat Modification .............................90

6.15.2 Mole and Vole Control Through Trapping ...............................................90

6.15.3 Mole and Vole Control Through Fumigants ............................................91

6.15.4 Mole and Vole Control Through Toxicants .............................................91

6.15.5 Mole and Vole Control Through Frightening ..........................................91

6.15.6 Mole and Vole Control Through Repellents .............................................91

6.15.7 Mole and Vole Control Through Shooting ...............................................91

6.16 River Otter Management Methods ....................................................................91
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6.16.1 River Otter Control Through Habitat Modification ................................. 91

6.16.2 River Otter Control Through Trapping .................................................... 92

6.16.3 River Otter Control Through Fumigants .................................................. 92

6.16.4 River Otter Control Through Toxicants ................................................... 92

6.16.5 River Otter Control Through Frightening ............................................... 92

6.16.6 River Otter Control Through Repellents ................................................. 92

6.16.7 River Otter Control Through Shooting ................................................... 92

6.17 Gopher Tortoise Management Methods ............................................................. 92

6.17.1 Gopher Tortoise Control Through Habitat Modification ......................... 92

6.17.2 Gopher Tortoise Control Through Trapping ............................................. 92

6.17.3 Gopher Tortoise Control Through Fumigants ......................................... 92

6.17.4 Gopher Tortoise Control Through Toxicants ............................................ 92

6.17.5 Gopher Tortoise Control Through Frightening ........................................ 92

6.17.6 Gopher Tortoise Control Through Repellents .......................................... 92

6.17.7 Gopher Tortoise Control Through Shooting ............................................ 92

6.18 Red Fox and Gray Fox Management Methods ................................................... 93

6.18.1 Red Fox and Gray Fox Control Through Habitat Modification ................. 93

6.18.2 Red Fox and Gray Fox Control Through Trapping ................................... 93

6.18.3 Red Fox and Gray Fox Control Through Fumigants ................................ 93

6.18.4 Red Fox and Gray Fox Control Through Toxicants .................................. 93

6.18.5 Red Fox and Gray Fox Control Through Frightening .............................. 93

6.18.6 Red Fox and Gray Fox Control Through Repellents ................................ 93

6.18.7 Red Fox and Gray Fox Control Through Shooting ................................... 93

6.19 Canada Goose Management Methods ................................................................ 93

6.19.1 Canada Goose Control Through Habitat Modification ............................. 93

6.19.2 Canada Goose Control Through Trapping ............................................... 94

6.19.3 Canada Goose Control Through Fumigants ............................................. 94

6.19.4 Canada Goose Control Through Toxicants ............................................... 94

6.19.5 Canada Goose Control Through Frightening .......................................... 94

6.19.6 Canada Goose Control Through Repellents ............................................. 95

6.19.7 Canada Goose Control Through Shooting ............................................... 95

6.19.8 Other Methods of Canada Goose Control ................................................ 95

6.20 American Alligator Management Methods ......................................................... 95

6.20.1 American Alligator Control Through Habitat Modification ..................... 95

6.20.2 American Alligator Control Through Trapping ........................................ 95

6.20.3 American Alligator Control Through Fumigants ..................................... 95

6.20.4 American Alligator Control Through Toxicants ....................................... 95

6.20.5 American Alligator Control Through Frightening ................................... 95

6.20.6 American Alligator Control Through Repellents ..................................... 95

6.20.7 American Alligator Control Through Shooting ....................................... 96

6.21 Ant Management Methods ................................................................................ 96

6.21.1 Ant Control Through Habitat Modification ............................................. 96

6.21.2 Ant Control Through Trapping ................................................................. 96

6.21.3 Ant Control Through Fumigants ............................................................. 96

6.21.4 Ant Control Through Toxicants ............................................................... 96

6.21.5 Ant Control Through Frightening ............................................................ 96

6.21.6 Ant Control Through Repellents .............................................................. 96

6.21.7 Ant Control Through Shooting ................................................................ 96
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7.0 Fiscal Considerations for Managing Animal Damage on Earthen Dams ................ 97

7.1 Fiscal Considerations for the Reluctant Dam Owner ............................................ 97

7.2 Fiscal Considerations of the Willing Dam Owner ................................................ 97

7.3 Overcoming the Economic Hurdles .................................................................... 98

8.0 References .............................................................................................................. 102

Appendix A ..................................................................................................................... 105

Appendix B ..................................................................................................................... 109
Chapter 1. Introduction and Purpose of Manual 1

1.0 Introduction and 

Purpose of Manual

1.1 Background

In 1999, the Federal Emergency Management Agency 

(FEMA) and the Association of State Dam Safety Officials 

(ASDSO) jointly conducted research and a workshop to 

shed light on the national problem of animal intrusion 

damage to earthen dams and the resulting safety issues. The 

FEMA/ASDSO survey and workshop united dam owners, 

engineers, state and federal regulators, wildlife managers, 

foresters, and academia to form an educated and experienced front against the growing problem of earthen dam 

damage and failures due to animal intrusion. The information generated by roundtable discussions and survey 

answers indicates that while most states recognize animal 

intrusion as a problem, only a handful know of guidance 

on dams and wildlife management practices available to 

the dam professionals and owners. Based on input from 

the dam communities, FEMA/ASDSO’s mission to develop 

a guidance manual on the proper management of nuisance 

wildlife in the earthen dam environment became clear.

To determine the information needs of the dam community—and therefore the most appropriate focus of this 

manual—FEMA/ASDSO issued a survey in 1999 and used 

the survey input from the 48 state dam safety officials 

representatives and 11 federal agencies representing the Interagency Committee on Dam Safety (ICODS). Additionally, 

a second survey was issued in 2003 to identify the current 

needs of each state, determine what nuisance wildlife and 

damages the states encounter, and understand which mitigation methods are being used with success or failure. Four 

main ideas emerged from the two survey efforts; these ideas 

consequently steered the direction of this manual:

Cumulatively, the states indicated a range of problems 

caused by numerous wildlife species relative to the 

operation of dams. This manual discusses 23 species 

with regard to their habitat, behavior, threat to dams, 

food habits, identifying characteristics, and management 

options: Muskrat, Beaver, Mountain Beaver, Groundhog, 

Pocket Gopher, North American Badger, Nutria, Prairie 

Dog, Ground Squirrel, Armadillo, Livestock (cow, sheep, 

horse, pig and wild pig), Crayfish, Coyote, Moles and 

Voles, River Otter, Gopher Tortoise, Red Fox and Gray 

Fox, Canada Goose, American Alligator, and Ants. 

While the states are fully aware of the potential adverse 

impacts wildlife activity can have on earthen dams (such 

as failure), private dam owners and local dam operators 

are often not aware of potential problems, and thus may 

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2 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

1.2 Target Audience, Purpose, and 

Application of This Manual

This manual provides technical guidance to dam specialists 

(including dam owners, operators, inspectors, state dam officials, and consulting engineers) in areas of focus identified 

through the two survey efforts and workshop. The purposes 

of this manual are to:

Assist dam specialists in understanding the impacts wildlife can have on earthen dams.

Provide dam specialists with basic information on habitat, range, description, and behavior of common nuisance wildlife to aid in their proper identification at the 

dam. 

Describe state-of-practice methods to prevent and mitigate adverse wildlife impacts on earthen dams.

Provide state-of-practice design guidance for repair and 

preventive design associated with nuisance wildlife intrusion.

It is envisioned that the entire dam specialist community 

will use this manual to augment their routine duties in 

earthen dam management. This manual is presented as 

a process toward dam inspection and management that 

includes wildlife damage identification and control. This 

manual provides technical information and guidance on: 

How wildlife damage adversely affects the safe operation 

of earthen dams; specifically, hydraulic alteration, internal and external erosion, and structural integrity losses 

(Chapter 2.0).

Dam inspections that incorporate a biological component 

to sensitize dam specialists to the aspects of their dams 

that attract wildlife and to understand where nuisance 

wildlife are likely to occur on the dam (Chapter 3.0).

Biological data for specific nuisance wildlife to assist 

the dam specialist in identifying which nuisance wildlife inhabits the dam. Biological data will also assist in 

controlling nuisance wildlife (e.g., listed food sources can 

be removed to encourage the animal to leave the area) 

(Chapter 4.0).

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•

•

•

•

•

25: number of states that 

indicate animal activity 

has caused or contributed 

to unsafe dam operation 

or outright failure within 

the state. 

9: number of states 

aware of information or 

guidance on the effects of 

animal activity on dams. 

not conduct inspections with wildlife damage in mind. 

Local dam owners may not typically mitigate existing wildlife intrusion problems or prevent them in the 

future.

States want to know how other states are successfully 

mitigating wildlife damages. Further, mitigation and 

prevention guidance should be developed and conveyed 

to the dam communities. 

Guidance booklets for local dam owners are needed to 

assist dam inspectors in identifying and mitigating animal intrusion issues.

Out of 48 states that responded to FEMA and ASDSO surveys, 25 document nuisance animals as the cause of dam 

failures or unsafe dam operations in their states. The U.S. Bureau of Reclamation, the National Park Service, and the U.S. 

Department of Agriculture document several similar cases 

at the federal level. State dam safety officials and federal 

agencies agree that animal burrows within dams can cause 

substantial and costly damage if left unmitigated and are 

consequently a major concern.

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Chapter 1. Introduction and Purpose of Manual

3

Dam design specifications and methods that can be 

incorporated into repair of existing dams or new dam 

designs to prevent wildlife intrusions (Chapter 5.0).

Guidelines to determine when wildlife management 

should occur at a dam (beyond dam repair and preven-

tion actions) and wildlife management methods that can 

be implemented when control of specific nuisance wild-

life populations is deemed necessary. Specific methods 

discussed include habitat modification, use of toxicants 

and fumigants, trapping, and shooting (Chapter 6.0). 

The fiscal issues related to appropriate and timely wildlife 

management at earthen dams (Chapter 7.0).

1.3 Technical Resources Cited

The technical information provided in this manual repre-

sents the most current practices in the areas of wildlife data 

and management and engineering inspection and repair, 

as they relate to nuisance wildlife and their effects on safe 

dam operations. While numerous technical sources are cited 

throughout the document, three main sources form the 

backbone of this manual’s technical understanding and rec-

ommendations. The first source is a manual titled Prevention 

and Control of Wildlife Damage (University of Nebraska, 1994). 

The data contained in the 1994 manual are considered the 

industry standard for pest control, and the manual is used as 

the handbook for those testing for licensure as pest control 

managers. It should be noted that the 1994 manual is under 

revision and a revised version will be completed February 

2005. Until the release of the revised manual, the 1994 edi-

tion remains the leading guidance literature in this field and 

is accepted as the most current practice in nuisance wildlife 

management (Smith, Pers. comm., 2003; 2004). The second 

source is a booklet called Prevention and Control of Animal Damage 

to Hydraulic Structures (USDA, 1991). The 1991 booklet adapts 

some of the 1994 manual data for application to the dam 

environment. The last source is technical data on remedial 

dam repair design by Dr. B. Dan Marks, as presented in the 

2001 ASDSO West Region Seminar on Plant and Animal 

Penetrations for Earthen Dams (ASDSO, 2001). Many other 

sources are also used throughout this manual to provide a 

cross-reference of data as well as a broad spectrum of infor-

mation. •••
4 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

2.0 Impacts of Wildlife 

on Earthen Dams

Figure 2-1. Upstream and downstream burrows can become dangerously close, causing internal erosion that may lead to dam failure. 

muskrat

burrow

dam crest

groundhog

burrow

water level

dangerously

close burrows phreatic surface

Earthen embankment dams are used by private landowners 

and state and federal agencies to store farm water supplies, 

city water supplies, recreational waters, flood waters, and 

wastewater lagoons. Earthen dams rely on a thick placement 

of compacted soils to withstand the water pressure of the 

pool contained behind the embankment. Often constructed 

outside of developed areas, the earthen dam environment 

is usually near a water source and can contain a variety of 

vegetation; given these characteristics, earthen dam environments can be naturally conducive to use by wildlife. Wildlife 

inhabiting the dam can alter the dam environment through 

habitat establishment and use—beaver build dams, muskrat 

excavate dens, livestock feed on stabilizing vegetation. The 

natural instincts of wildlife to adapt and use their environment toward their survival can compromise the balance 

of engineered functions that maintain the viability of an 

earthen dam. 

The first step in fortifying a dam against unsafe operations 

caused by wildlife damage is to understand what could go 

wrong if wildlife damage is left unchecked. While a dam 

owner may observe a few small burrows on the upstream 

and downstream slopes, it is important to understand that 

potential problems, like those burrows, often run deep 

below the surface. As such, the purpose of this Chapter is to 

discuss adverse engineering effects stemming from nuisance 

wildlife activity. Adverse effects caused by specific wildlife 

(as well as their identification and mitigation) are discussed 

in Chapters 4.0, 5.0, and 6.0.

2.1 Background

Embankment dams are vulnerable to damage from wildlife 

intrusions. Twenty-five states indicate that animal activity 

has caused or contributed to unsafe operation or outright 

failure of an embankment dam. Several animal species excavate burrows, tunnels, and den entrances for shelter, while 

other predatory animals will enlarge these structures via 

digging in search of prey. Similarly, herbivorous species will 

forage on vegetation growing on embankment dams. All 

of these occurrences create open areas in the embankment 

fill which are detrimental to the safety and performance 

of embankment dams. Some of these effects can be easily identified, such as surface erosion; other effects such as 

internal erosion may not become visible until dam safety is 

jeopardized.
Chapter 2. Impacts of Wildlife on Earthen Dams 5

of soils in the dam, and variability of the reservoir normal 

pool. As such, each dam has a unique flownet. The presence 

of animal burrows, either on the upstream or downstream 

slope, can distort the established phreatic surface and impact 

the flownet. As illustrated on Figure 2-2, upstream burrows 

can allow the normal pool elevation to extend into the dam 

embankment, forcing the phreatic surface further into the 

embankment. Likewise, downstream intrusions can allow 

the phreatic surface to day-light higher on the downstream 

slope. The overall effect can be a significant alteration to the 

phreatic surface. Dramatic changes to the phreatic surface can shorten seepage paths, increase seepage volumes, 

decrease the factor of safety against slope failure, and cause 

internal erosion of embankment materials (piping). 

Of these impacts, piping is most often cited as the greatest 

concern among dam safety professionals because it is progressive and can rapidly lead to failure of the dam. Piping 

is the uncontrolled movement of soil particles caused by 

flowing water. As shown on Figure 2-3, piping will often 

start in a burrow on the downstream slope. Flowing water 

moves soil particles from the embankment to the burrow, 

leaving a void that is quickly filled with soil particles from 

deeper within the embankment. Because water pressure and 

flow generally increase further into the dam embankment, 

the rate of movement of soil particles will also increase. 

A pipe is rapidly formed extending from the downstream 

slope to the upstream slope. A dam breach is almost certain 

to develop in these instances.

External problems can also arise from wildlife activity 

around an embankment dam. Though hydraulic barriers 

can result from the activities of several species, beaver cause 

perhaps the largest array of adverse effects. To create deep 

waters in which to hide from predators, beavers compact 

felled tree trunks, limbs, and other materials into a mound 

to restrict the natural flow of a water source. As a result, 

the hydraulic function of the dam is altered in several ways. 

First, beaver mounds may block principal and emergency 

spillways and riser outlets, resulting in increased normal 

pool levels and reduced spillway discharge capacity. Second, 

sudden high discharges from the dam could occur if the 

beaver dam fails. Third, beaver dams located upstream of 

the embankment dam can clog water control structures as 

debris from the beaver dam floats downstream. Finally, erosion of the downstream toe of the dam can occur as a result 

of elevated tailwater caused by beaver activity.

Homogeneous and zoned 

embankment dams are 

equally susceptible to 

damage from animal 

intrusions. The ultimate 

consequence from the 

intrusions depends on the 

specific engineering and 

biological characteristics 

of an individual dam. 

Embankment dams can be generally categorized as either 

homogeneous (containing one material) or zoned (containing multiple materials). Zoned embankment dams usually 

contain a central core designed to produce a lower phreatic surface (static water level within a dam embankment) 

within the downstream slope than the theoretical surface 

often assumed for homogeneous embankments. Due to the 

variability of zoned embankments, this manual discusses 

only homogeneous embankments.

2.2 Hydraulic Alteration

The most significant and often least obvious impact of wildlife intrusions on embankment dams is hydraulic alteration. 

Hydraulic alteration and its effects can manifest in different ways depending on the type and location of intrusion, 

including flownet distortion and physical barriers to flow. 

A distorted flownet may not be a visible problem but it can 

have the most dramatic impact. Flownet is a term referring 

to the theoretical description of water flow through and 

under an embankment dam. The phreatic surface, equal potential lines and flow lines associated with a flownet are defined by the physical dimensions of the dam, classification 
6 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

2.3 Structural Integrity Losses 

Wildlife excavate dens, burrows, and tunnels within embankment dams, causing large voids that weaken the 

structural integrity of the dam. Typical voids can range 

from the size of a bowling ball to a beach ball and much 

larger. Heavy rain and snow melt loosen soils surrounding 

a burrow, causing a localized collapse inside the burrow. In 

addition, a burrowing animal may encounter loose zones in 

the embankment (due to variability of constructed embankments) during burrow excavation, leading to a localized 

collapse. Animal dens also erode and collapse under the load 

of heavy equipment and other vehicles that use the crest of 

the dam as a throughway.

The collapsing soils will progressively lead to sinkholes or 

depressions appearing on the embankment surface. Because 

burrows can be under several feet of soil, the deformation 

or sinkhole visible at the surface could be several times the 

size of the original burrow. As illustrated on Figure 2-4, 

the collapsed soils can represent a significant portion of the 

dam embankment. Under the right circumstances, localized 

slope instability can result from a collapsed animal burrow. 

Depending on the location and number of collapsed burrows, dam safety or operation could be jeopardized. If portions of the crest are affected, a loss of freeboard can result, 

thus endangering the dam during storm events. Downstream slope failures, regardless of their extent, weaken 

embankment soils and reduce confinement of surrounding 

soils, thereby resulting in further weakening of embankment soils. Depending upon site and weather conditions, 

the process can progress slowly or rapidly, potentially leading to massive slope instability.

2.4 Surface Erosion

The foraging behavior of some animals on open area vegetation associated with dam embankments can reduce or 

eliminate vegetative cover on a dam. This increased feeding pressure on the dam’s vegetative groundcover can lead 

to erosion paths and decreased soil retention on the dam’s 

crest and slope. In addition, dams that are grazed by liveFigure 2-3. Burrows can lead to piping within an embankment. 

process continued 

over time

soil movement

into burrow

Figure 2-2. Burrows can alter dam hydraulics by shortening seepage paths.

burrow

theoretical

phreatic surface

altered phreatic surface

groundhog den
Chapter 2. Impacts of Wildlife on Earthen Dams 7

Figure 2-4. Burrows can collapse, leading to formation of sinkholes and loss of structural integrity.

collapse

theoretical seepage line

stock often show increased rates of soil erosion because of 

the lack of stabilizing vegetation from grazing and trafficking, which can lead to irregular surface erosion and the 

formation of rills and gullies. 

With continued neglect, these areas will require more than 

simple maintenance. In fact, given enough time, external 

erosion can lead to a reduction in freeboard and loss of 

cross section. In turn, these impacts can increase the dam’s 

vulnerability to damage from high water during large storm 

events.
8 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

3.0 Dam Inspection From 

Two Perspectives: 

Engineering Function and 

Biological Potential 

The second step toward fortifying a dam against the effects of nuisance wildlife damage is the observation of clues 

left by wildlife in the dam environment. As such, regular 

inspection of the dam that incorporates wildlife activity 

recognition must be conducted by the dam owner, who is 

the first line of defense in protecting earthen dams. While 

the dam inspection is focused primarily on seepage, deformation, and structural deficiencies, the inspectors must 

also perceive wildlife clues left behind by dam inhabitants 

whose presence could cause trouble down the road. Toward 

this goal, this Chapter details an inspection procedure that 

pairs engineering inspection with key biological considerations to assist the dam specialist in viewing the dam from 

both perspectives (this methodology should be applied using the specific wildlife clues data presented in Chapter 4.0 

of this manual). 

3.1 Wildlife And The Earthen Dam 

Through their natural desire to create dens, search for food, 

or escape predators, wildlife can cause a host of adverse 

impacts to an earthen dam which can lead to dam failure 

(refer to Chapter 2.0 of this manual for detail on the adverse 

impacts of wildlife activities). Though earthen dams are 

manmade, wildlife interacts with the earthen dam environment as if it were natural field or forest. To protect their 

dams, dam owners should know the biological potential of 

their dams—can wildlife find a suitable environment at the 

dam, and if so, which kind of wildlife will inhabit which 

locations of the dam? In answering these questions, it is 

helpful to know the characteristics that compose favorable 

habitat, and to realize that dams with diverse vegetation 

and site features often support a wide variety of wildlife. 

In assessing the dam for its biological potential, review the 

following relative to the dam area and surrounding areas 

(adapted from Benyus, 1989):

Vegetation Vitality: Do the dam and adjacent areas contain dense vegetation at all levels (e.g., grass, shrub, and 

tree)? In general, greater variety of dense vegetation at 

levels ranging from groundcover to understory to canopy 

(regardless of vegetation type) allows for a greater variety 

of wildlife to inhabit the area. Small mammals, such as 

those discussed in this manual, prefer sites with adequate 

vegetation cover to hide from predators (see Chapter 5.2 

for a discussion on appropriate vegetation at a dam).

•
Chapter 3. Dam Inspection from Two Perspectives: Engineering Function and Biological Potential 9

Mini-habitats: Do the dam and surrounding area offer 

vegetative diversity? Different landscapes such as prairie 

and forest? Sun and shade? Deep and shallow water? An 

environment with a mosaic landscape provides several 

habitat types in one area, which can support a wider 

variety of wildlife.

Transition Zones: Is there a clear edge between one 

habitat type and another? At the dam environment, the 

dam area (a lake/pond environment) may be surrounded 

by a grassy field environment, a shrub edge, or a forested 

environment. The junction where two environments 

meet is called an edge, and edges are the most heavily 

trafficked areas in an environment (a good place to view 

the wildlife in and around the dam area) because they 

provide safe travel corridors between the two habitat 

types and create a more diverse habitat than either of the 

two habitat types. 

Size: Does the dam environment provide a large land area 

that allows wildlife to meander without having to cross 

roadways or come into contact with people? Most species 

of wildlife prefer large parcels of land that provide habitat variety without human influence. 

Unique Characteristics: Does the dam contain unique 

land features? By its very nature, the dam environment 

is unique because it contains a water source. Wildlife 

prefers a constant water source, so dams with a permanent pool will be preferable to those with a fluctuating 

pool, such as those used for flood control or irrigation. 

However, any water source will attract wildlife to some 

degree.

3.2 Two-Perspective Dam Inspection Methodology 

The typical dam safety inspection checklist requires observation of every dam feature. The checklist is developed by 

an individual state’s dam safety program or federal organization such as the U.S. Bureau of Reclamation, U.S. Army 

Corps of Engineers, U.S. Fish and Wildlife Service, or the 

Federal Energy Regulatory Commission. All inspections 

focus on distinct physical regions, although the inspection 

checklists vary in length, listed inspection items, and required observations. Generally, the features are divided into 

clear components including:

Upstream Slope

Downstream Slope

Crest

•

•

•

•

•

•

•

Embankment-Abutment Contact (Groin)

Principal Spillway

Emergency Spillway

Lake Drain or Outlet Works

Although inspection for animal intrusions is a facet of 

most if not all state inspection checklists, it is certainly not 

a major part of the inspection. Specific guidance on identifying animal intrusions or the typical intrusion locations 

of specific animals is not provided on the checklists. An 

inspector lacking this information may be unable to adequately inspect their dam for animal intrusions, much less 

adequately identify and mitigate the nuisance animal. As 

such, this manual presents an inspection methodology that 

combines engineering and biological considerations, which 

when viewed together, allow a dam specialist to view the 

dam comprehensively.

For the purposes of this manual, the dam is divided into 

six zones: Upstream Slope, Dam Crest, Upper Downstream 

Slope, Lower Downstream Slope, Downstream Toe, and Spillway, Outlets, and General Areas (Figure 3-1). The risk posed 

by animal intrusions is greater in some zones than in others. 

As such, the zones are overlapped to emphasize the critical nature of the area and to require inspection of the area 

twice to ensure that biological clues are sighted (ASDSO, 

2001). Further discussion of the six zones relative to risk, 

restoration, and repair of animal intrusions is provided in 

Chapters 5.3 and 5.4. 

When considering animal intrusions, inspection of each 

zone should consider not only physical evidence of an 

animal presence (e.g., burrow entrance), but also the habitat 

and biological factors that attract wildlife to the dam and 

sustain them once they have become established (Figure 

3-2). Understanding both the engineering and biological 

aspects of animal intrusions into embankment dams is critical in eliminating or at least controlling the intrusions. 

3.2.1 Zone 1: Upstream Slope Area

Engineering Perspective: The goal of inspecting the upstream slope of the earthen dam is to see the entire surface clearly. To ensure the inspector views the entire slope 

surface, the inspector must walk back and forth across the 

slope utilizing one of two patterns: zig-zag or parallel. In 

general, the zig-zag method is best for small dams and mild 

slopes (Figure 3-3, shown on page 17). It may prove difficult to move in a zig-zag pattern on large dams and steeper 

slopes, and in these cases the parallel pattern is suggested 

(Figure 3-4, shown on page 17). 

•

•

•

•
10 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

While walking the slope, the inspectors should routinely 

stop and view the alignment of the surface by turning their 

gaze a full 360 degrees. Checking the slope frequently and 

from many viewpoints and distances can reveal deficiencies 

and distortions (such as surface distortions or vegetation 

changes) that might otherwise go undetected. The inspectors should observe berms on the upstream slope by centering their eyes on the line being viewed and moving their 

body from side to side to view the line from several angles. 

This approach will help the inspector identify misalignments. 

A typical dam safety inspection report should comment on 

vegetation, slope protection, erosion, instabilities, and animal burrows observed in Zone 1. When specifically considering animal burrows and other deficiencies resulting from 

animal activity, the inspector should look for the following: 

animal burrow entrances, mounds of excavated soil, debris 

(evidence of beaver activity), cracks, depressions, erosion, 

sinkholes, paths and ruts, sloughs, slides, and scarps. These 

conditions often indicate damaging animal activity. The 

inspection report should note whether the deficiencies warrant monitoring, repair, or further investigation.

Zone 1 Upstream 

slope area 

Zone 2 Dam crest area

Zone 3 Upper downstream 

slope area

Zone 4 Lower downstream 

slope area

Zone 5 Downsteam 

toe area

Zone 6 Spillway, outlets 

(not shown)

crest

zone 1 zone 3

zone 2

zone 4

zone 5

theoretical seepage line

H/2

H/2

H/3

4’

Figure 3-1. Dam Inspection Zones.

phreatic surface

Biological Perspective: This zone is primary habitat for 

aquatic burrowers such as muskrat and beaver, which generally burrow from 6 inches to 4 feet below the water line 

upward toward the crest. Nutria prefer to dig dens in the 

zone where land and water meet, which could be dominated by aquatic vegetation. River otters are often found living 

in abandoned muskrat, beaver, and nutria burrows, and can 

construct slides on slopes and bare areas where they repeatedly enter and exit the water. Livestock often traverse the 

upstream slope area—look for hoof tracks, rills, and eroded 

pathways. Canada geese and livestock feed on embankment 

slopes causing eroded areas and ruts. Crayfish and alligator 

may inhabit the banks and shallows of the upstream slope 

area. Ants may dig tunnels in the slope, loosening existing 

cracks. Mountain beaver or armadillo may be found along 

the wet edge of the pond, especially if a forest fringe or 

wooded area is nearby. Moles may hunt in the moist soils 

near the reservoir.

3.2.2 Zone 2: Dam Crest Area

Engineering Perspective: Similar to inspecting the upstream slope, the crest can be viewed using either a zig-zag 

or parallel pattern, with the primary goal being to view the 
Chapter 3. Dam Inspection from Two Perspectives: Engineering Function and Biological Potential 11

Upland Areas. Many species live in the upland 

areas, away from the water. Even the downstream 

slope, abutments, and groin areas of the dam can 

be considered upland in terms of habitat. 

Forest Fringe. The zone between two environments (the 

edge) is the best place to observe those species living at 

and around the dam. The more habitat types at the dam, 

the greater number of species likely to inhabit the dam. 

Mountain beaver or armadillo prefer forested/wooded areas.

Emergency Spillway. Beaver often dam the 

spillway, causing the pond water levels to rise. 

Left Abutment contact.

Inappropriate Vegetation on Embankment. Many 

dams contain vegetation other than mowed grass. 

Improper vegetation provides cover and food supply, 

which encourage animals to inhabit the dam. 

Downstream Slope. This area is often the location where 

groundhogs, coyote, and fox excavate burrows. Canada 

geese will feed on the downstream slope, which could cause 

loss of protective vegetative cover and associated erosion. 

Species that prefer upland areas could be found in this area.

1.

2.

3.

4.

5.

6.

Left Groin.

Discharge Conduit and Outlet Channel. Beaver can dam 

the outlet structure. Aquatic species may inhabit this area 

depending on water flow and availability of vegetation.

Toe of Embankment and right groin.

Erosion Pathways on the Embankment. Livestock 

traverse the embankment creating erosion pathways. 

Right abutment contact.

Crest. Livestock traverse the crest which creates ruts. 

The ceilings of beaver and muskrat burrows in the 

upstream slope are often just below the dam crest. 

Aquatic Fringe. The zone where the bank meets 

the pond usually contains aquatic vegetation 

preferred by many animals such as nutria.

Upstream Slope. Beaver, muskrat, and nutria 

prefer the upstream slope for burrow excavation. 

Alligators, otters, and turtles usually live in the 

shallow waters near the upstream slope. 

Principal Spillway (with riser and trash rack). Beavers 

can block principal spillways by constructing dams.

7.

8.

9.

10.

11.

12.

13.

14.

15.

Figure 3-2. The Earthen Dam from Biological and Engineering Perspectives.
12 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

entire crest from several perspectives and distances. Similar 

to the upstream slope inspection, the inspectors should center their eyes on the crest line, moving their body from side 

to side to view the line from several angles. Fixed features 

that can mark horizontal and vertical points along a dam 

can be used as reference lines; guardrails, a row of posts, or 

parapet walls are good reference lines (use caution when 

using man-made reference lines which can be moved). The 

reference line must be viewed from several different perspectives; first, the inspectors should sight directly on the 

reference line and then move their body to either side. This 

method will assist the inspector in detecting a change in the 

uniformity of the crest. Zone 2 overlaps Zone 1 on one-half 

of the crest width. This is intentional, and is meant to emFigure 3-3. The zig-zag method of inspection is 

best used on small dams and mild slopes.

Figure 3-4. The parallel method of inspection is 

best used for dams with steep slopes.

phasize the critical nature of the area by requiring inspection of the area twice (ASDSO, 2001).

A typical dam safety inspection report should comment 

on width, alignment, vegetation, erosion, instabilities, and 

animal burrows observed in Zone 2. When specifically 

considering animal burrows and other deficiencies resulting from animal activity, the inspector should observe the 

following: animal burrow entrances, mounds of excavated 

soil, cracks, depressions, erosion, sinkholes, paths and ruts, 

sloughs, slides, and scarps. As with Zone 1, these issues can 

indicate animal activity. The inspection report should note 

whether the deficiencies warrant monitoring, repair, or 

further investigation.

Biological Perspective: Dens of beaver and muskrat are typically located just below the crest (look for depressions in 

the crest since the burrow entrance is typically underwater), 

and livestock often traverse the crest (look for hoof tracks, 

rills, gullies, and eroded pathways). Terrestrial wildlife such 

as groundhogs, ground squirrels, pocket gophers, foxes, 

coyote, and badgers may inhabit or hunt in the crest area. 

Moles may dig burrows in the dry, upland area of the upper 

upstream slope/crest that lead to their hunting grounds in 

the cool, moist soils near the reservoir pool. Vehicular traffic 

on crests may discourage wildlife establishment. Additionally, the crest is often constructed of well-compacted material, 

which is not attractive to most burrowing wildlife. Ants may 

dig tunnels in the crest, loosening existing cracks.

3.2.3 Zone 3: Upper Downstream Slope Area

Engineering Perspective: Inspecting the downstream slope 

is similar in method to inspecting the upstream slope. It 

is suggested that the downstream slope be viewed from a 

distance at a time of day when the angle of the sun is low 

so that wet areas, which will reflect sunlight, are seen more 

easily. Zone 2 overlaps Zone 3 on one-half of the crest in 

order to draw additional attention to the crest area. 

A typical dam safety inspection report should comment 

on alignment, vegetation, erosion, instabilities, and animal 

burrows observed in Zone 3. When specifically considering animal burrows and other deficiencies resulting from 

animal activity, the inspector should observe the following: 

animal burrow entrances, mounds of excavated soil, cracks, 

depressions, erosion, sinkholes, paths and ruts, sloughs, 

slides, and scarps. As with the previous zones, these issues 

can indicate animal activity. The inspection report should 
Chapter 3. Dam Inspection from Two Perspectives: Engineering Function and Biological Potential 13

note whether the deficiencies warrant monitoring, repair, or 

further investigation.

Biological Perspective: This zone is the most attractive 

for terrestrial animal activity and is preferred by groundhog, fox, and coyote for burrow and den sites. Prairie dog, 

pocket gopher, ground squirrel, and groundhog may inhabit 

the downstream slope area; if they do, predators such as 

badger, coyote, and foxes may choose this zone as a hunting ground. Gopher tortoises, which are strictly terrestrial, 

would prefer this zone as it is dry and located well-above 

the phreatic surface. Look for large dens, burrows, and piles 

of dirt outside of small burrows. Ants may dig tunnels in the 

slope, loosening existing cracks. Livestock and Canada geese 

may graze on the stabilizing vegetation. Moles may inhabit 

this area and dig burrows from the slope area to an adjacent 

outlet or spillway for the moist soils they prefer as a hunting 

ground. Armadillo, mountain beaver, or voles may inhabit 

this area if the dam is improperly vegetated with trees, 

shrubs, or a thick understory.

3.2.4 Zone 4: Lower Downstream Slope Area

Engineering Perspective: Inspection of this zone is similar 

to inspecting the upstream and upper downstream slopes, 

but the inspector should give greater scrutiny to the downstream slope below the pool elevation. In most embankment 

dams, the potential for seepage through the embankment 

materials day-lighting on the downstream slope increases 

dramatically further down the downstream slope. As shown 

on Figure 3-1, the theoretical phreatic surface typical for 

homogeneous embankment dams intersects the downstream slope. Therefore, the presence of an animal burrow 

in this area could shorten seepage paths, increase hydraulic gradients, and ultimately cause internal erosion of the 

embankment materials. A more detailed description of the 

potential impacts from animal intrusions is provided in 

Chapter 2.0.

A typical dam safety inspection report should comment 

on vegetation, erosion, instabilities, seepage, and animal 

burrows. The potential for uncontrolled seepage through 

animal burrows in Zone 4 is significantly greater than in the 

three previous zones. Therefore, seepage observations are 

important in Zone 4. When specifically considering animal 

burrows and other deficiencies resulting from animal activity, the inspector should scrutinize the following: animal 

burrow entrances, mounds of excavated soil, concentrated 

seeps, wet/spongy areas, cracks, depressions, erosion, sinkholes, paths and ruts, sloughs, slides, and scarps. As with 

previous zones, these issues can indicate animal activity. The 

inspection report should also note whether the deficiencies 

warrant monitoring, repair, or further investigation

Biological Perspective: This zone would also likely support terrestrial wildlife as described under Zone 3. Burrows 

constructed in lower Zone 4 (where it overlaps with Zone 

5) will become saturated depending on depth, which is not 

preferred by most burrowing animals; therefore, burrows 

of terrestrial animals (i.e., gopher tortoise, fox, coyote, and 

groundhog) will occur in upper Zone 4. If a resident beaver 

constructs a dam that retains water, then muskrat, beaver, 

and otter will occupy inundated downstream slopes and 

outlet areas. Moles may hunt in the downstream slope if 

soils are moist, and the mountain beaver or armadillo may 

inhabit this area if the vegetation includes trees, shrubs, and 

a thick understory. Ants may dig tunnels in the slope, loosening existing cracks. Livestock and Canada geese may graze 

on stabilizing vegetation.

3.2.5 Zone 5: Downstream Toe Area

Engineering Perspective: Inspection of this zone is similar 

to inspecting the upstream slope and upper/lower downstream slopes, but Zone 5 is the most critical area because 

of the potential proximity of the phreatic surface to the 

downstream slope in this zone. Therefore, as in Zone 4, the 

presence of animal burrows in this area could shorten seepage paths, increase hydraulic gradients, and ultimately cause 

internal erosion of the embankment materials. 

A typical dam safety inspection report should comment 

on vegetation, erosion, instabilities, seepage and animal 

burrows in Zone 5. The potential for uncontrolled seepage 

through animal burrows in Zone 5 is significantly greater 

than in Zones 1 through 3, and somewhat greater than in 

Zone 4. Therefore, seepage observations are critical in Zone 

5. When specifically considering animal burrows and other 

deficiencies resulting from animal activity, the inspectors 

should observe the following: animal burrow entrances, 

mounds of excavated soil, concentrated seeps, wet/spongy 

areas, cracks, depressions, erosion, sinkholes, paths and ruts, 

sloughs, slides, and scarps. As with previous zones, these 

issues can indicate animal activity. The inspection report 

should note whether the deficiencies warrant monitoring, 

repair, or further investigation.

Biological Perspective: Burrows constructed in Zone 5 

will become saturated depending on depth, which is not 

preferred by burrowing terrestrial animals (i.e., armadillo, 
14 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

mountain beaver, vole, mole, gopher tortoise, fox, coyote, 

and groundhog). If a resident beaver builds a dam that 

retains water, then muskrat, beaver, nutria, and otter will 

occupy inundated downstream slopes and outlet areas, if 

appropriate vegetation has become established. Ants may 

dig tunnels in the slope, loosening existing cracks. Livestock 

and Canada geese may graze on stabilizing vegetation.

3.2.6 Zone 6: Spillway, Outlets, and General Areas 

Engineering Perspective: The best approach to inspecting 

spillways and outlets is to view all surface and internal areas 

by walking closely along or within the structure, observing 

confined space entry requirements. The inspector should 

enter the conduit and view the internal structure using a 

flashlight, providing the conduit is of the appropriate size 

and in safe repair. The inspector should use binoculars or 

a camera/video camera with the appropriate lens to document the conduit condition if the conduit is not accessible 

(e.g., located in the water separated from the shoreline or 

embankment). Underwater features can be viewed via use 

of boats or underwater divers. Shorelines and upstream 

areas should be inspected by walking or using vehicles 

to traverse the inspection areas. Other appurtenant works 

should be inspected up-close. 

Biological Perspective: Beaver will construct dams at the 

spillway locations to capture and reroute water flow. Look 

for gnaw marks in a circular pattern on tree trunks, beaver 

dams, and otters playing in the beaver dam waters. Aquatic 

animals such as muskrat and nutria may be found at these 

locations if the beaver dam retains water, and if sufficient 

aquatic vegetation has become established. Armadillo or 

mountain beaver may inhabit the area if a forest fringe or 

wooded area is adjacent to the water source.
Chapter 4. Overview and Identification of Nuisance Wildlife 15

4.0 Overview and Identification 

of Nuisance Wildlife

The FEMA/ASDSO workshop and 2003 dam safety specialist 

surveys indicate that several species damage earthen dams 

across the nation. This Chapter discusses 23 animals identified by the states as presenting the greatest threats to safe 

dam operations. Tracks, photographs, and range maps are 

provided for each animal, as well as a description of the 

specific threats each animal poses to the earthen dam environment, its preferred habitat, food habits, behavior, and 

field-identifying tips specific to each animal. It should be 

noted that some information is difficult to present depending on the animal (e.g., crayfish tracks) and in these cases, 

such information is omitted.

In a general sense, it is envisioned that a dam specialist will 

use this information to gain a better understanding of the 

wildlife that inhabits a dam. To a greater degree, it is hoped 

that this information will go hand in hand with overall dam 

management to assist a dam specialist in knowing where to 

look for wildlife damage (e.g., burrow sites), indicate which 

animals caused the damage via specific descriptors, and 

lead the dam specialist toward appropriate damage repair, 

prevention, and wildlife management (see Chapters 5.0 and 

6.0 for dam repair, damage prevention, and wildlife management methods). 

4.1 The Importance of Accurate Wildlife Identification

During the regular dam inspection detailed in Chapter 3.0 

of this manual, the dam specialist will have viewed the dam 

from both engineering and biological perspectives. In doing 

so, the specialist may have identified burrows just below 

the water-line, observed floating rafts of vegetation on the 

water, trails from the water to the bank, and noted an abundance of aquatic vegetation along the shoreline. Application of the information in this chapter will assist the dam 

specialist in putting the above clues together to determine 

which animal is damaging the embankment.

Given the dynamic nature of wildlife and its desire to avoid 

human interaction, a dam owner will seldom witness wildlife causing damage to dams. However, proper identification 

of nuisance wildlife is critical so that dam repair and wildlife management methods can be appropriately and lawfully 

applied to mitigate specific species and their impacts to the 

earthen dam. 

A dam environment that has high biological potential (refer 

to Chapter 3.1 for discussion of biological potential) will 

most likely support several nuisance species; however, not all 
16 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

species living at the dam are necessarily in need of management. To apply mitigation that blankets all animals seen at 

the dam may be a waste of time and money, not to mention 

unnecessarily damaging to the environment. For this reason 

it is important to carefully evaluate the biological evidence 

at the dam to accurately identify the species responsible for 

the damage. For example, beaver and otters often live in the 

same environment, and otters often opt to use beaver dens 

instead of creating their own. In this case, the otter may be 

seen living in the den, but the beaver is the species actually 

responsible for the burrowing activity. Therefore, mitigation should be geared toward the beaver, and not necessarily 

the otter, which will live in hollow logs and rock crevices 

just as comfortably. On the other hand, several species may 

be responsible for compromising activities at the dam, and 

dam repair, prevention action, and wildlife mitigation will 

need to be geared toward several species. In essence, application of the information provided in this Chapter will assist 

in accurate identification of the problematic species, which 

will help the dam specialist appropriately manage the dam 

without spending unnecessary energy or funds. 

Misidentification of a 

wildlife species may result 

in inadequate mitigation, 

which could allow damage 

to continue, perhaps leading 

to dam failure. As wildlife 

identification can be 

difficult, a dam owner may 

benefit from using a wildlife 

specialist or professional 

trapper to positively identify 

the species so that proper 

wildlife mitigation can 

be developed. Appendix 

A contains state wildlife 

contacts, and state 

trapper information can 

be obtained at www.

nationaltrappers.com. 
Chapter 4. Overview and Identification of Nuisance Wildlife 17

4.2.1 Muskrat Overview

4.2 Identifying Nuisance Wildlife 

Threat to Dams: Muskrats dig fairly large burrows that can 

lead to internal erosion and structural integrity losses in the 

earthen dam. Muskrats will continue to dig upward into the 

embankment as the phreatic surface rises; internal burrows 

can become extensive.

Habitat and Home (Figure 4-1): Muskrat inhabit freshwater 

and saltwater marshes, lakes, ponds, rivers, and other watercourses, where water is calm or very slowly moving. Muskrats prefer water courses that are about 3-4 feet deep that 

don’t freeze completely in the winter and contain abundant 

cattails or aquatic vegetation. Muskrats typically burrow 

Muskrat(Ondatra zibethicus) are semi-aquatic rodents with brownishblack fur and with a body 10-14 inches long and a tail 8-11 inches 

long. Muskrats have large, partially-webbed hind feet and a vertically 

flattened tail, which they use to propel themselves through water. 

Figure 4-1. Muskrat dig dens in the upstream slope, with the entrance tunnel beginning about 6-18 inches below the water line.
18 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

walking

forefoot hindfoot

into a dam’s upstream face. Their burrows begin from 6 to 

18 inches below the water surface, and breather holes and 

escape holes can be observed above the water line. If the 

water level rises, the muskrat will excavate a dry chamber 

by digging higher into the embankment at an upward slant. 

Muskrats also build conical houses out of marsh vegetation, but usually excavate and use burrows when inhabiting 

earthen dams and other hydraulic structures (USDA, 1991). 

Detection of muskrat can be difficult if slopes of the dam 

are improperly vegetated, as their burrows may be covered 

over (see Chapter 5.2 for a discussion on improper vegetation at an earthen dam).

Range of the muskrat in North America.

In very clear tracks, a small fifth toe can be seen on the 

outside of the front foot pad. All toes, except the nubbin, will 

show claw prints. The muskrat’s vertically flattened, bare tail 

will create a drag mark in the center of the prints.

Muskrats are considered 

a significant dam 

safety issue in 71% of 

the surveyed states.

Food Habits: Muskrats are primarily herbivores and prefer to 

feed on cattails, grasses, smartweed, duck potato, water lily, 

sedges, and other aquatic plants. When vegetation is scarce, 

muskrat will feed on bivalves, crustaceans, insects, and 

sometimes fish (University of Nebraska, 1994). 

Behavior: Muskrats can often be seen swimming at any hour 

of the day however they are most active at twilight. Muskrats often construct roofs over floating rafts of vegetation 

so that they have a covered place to eat. These huts can be 

found floating on the water and are especially important 

to the muskrat in winter when cooler weather can chill the 

animal’s naked tail and feet (USDA, 1991; Benyus, 1989).

Field Tip: Listen for a loud splash when nearing the water. 

Muskrats plop into the water when approached to alert 

other muskrat of human activity. Muskrats sometimes hold 

their tails out of the water as they swim (Benyus, 1989). 
Chapter 4. Overview and Identification of Nuisance Wildlife 19

4.2.2 Beaver Overview

The Beaver (Castor canadensis) is the largest rodent in North America 

weighing 45-60 pounds, with a body measuring 25-30 inches 

and a tail measuring 9-10 inches. Beavers are typically aquatic 

mammals, with webbed feet that are adapted for swimming and a 

flattened tail. Beavers vary in color but the most common body fur is 

reddish-brown and the belly fur is usually gray (USDA, 1991). 

Threat to Dams: Beaver can cause extensive damage to earthen 

dams by excavating bank burrows, which can cause internal 

erosion or structural integrity losses. Beaver dams constructed across spillways can cause adverse hydraulic effects and 

result in flooding or failure of the spillway or the earthen 

dam itself. Beavers often clog the intake and outlet structures with their cuttings.

Habitat and Home: (Figures 4-2, 4-3, 4-3A and 4-4): Beaver can be found throughout the continental United States 

wherever there is a year-round source of water. However, 

beaver will avoid an aquatic site that does not contain 

preferred foods or have adequate sites for lodges, dens, or 

dams (University of Nebraska, 1994). Beaver lodges are 

easy to identify; they are dome-shaped, built of limbs and 

Beavers are considered 

a significant dam 

safety issue in 67% of 

the surveyed states. 

dam crest

den

Figure 4-2. The ceiling of a beaver den is often just below the crest of the dam.
20 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

walking

forefoot hindfoot

Beaver dens are often 

excavated just below the 

dam crest within the dam. 

A den roof collapse at this 

location can create voids in 

the crest and upstream slope. Range of the beaver in the North America.

Beaver tracks are not a reliable way to identify their presence due to 

their walking pattern. The beaver’s hind foot is placed on top of the front 

foot’s track and the wide tail, which drags along the ground, smears 

both to a point where identification becomes nearly impossible.

logs, may reach 5-6 feet above the water line, and be 12-14 

feet wide (Benyus, 1989). Beavers have also been known to 

create tunnels and dens. Beaver tunnel entrances have been 

observed 1-4 feet below the water level. Beavers burrow 

into the dam from below the water line upwards toward the 

crest, where the beaver will excavate their den. The entrance 

to the lodge or bank den is typically under water, with the 

interior den being several inches above the water surface. 

All lodges and bank dens have at least two entrances, and 

perhaps four or more (University of Nebraska, 1994).

Food Habits: Beaver prefer to eat tree species such as aspen, 

willow, poplar, cottonwood, sweetgum, blackgum, and 

pine, although beaver will also eat most woody plants that 

grow near water, as well as herbaceous and aquatic plants. 

Beavers will travel 100 yards or more from their water habitat to cut down crops or trees growing in adjacent habitats 

and drag them back to their pond home. Beaver use whatever vegetation they don’t eat for dam construction (University of Nebraska, 1994).
Chapter 4. Overview and Identification of Nuisance Wildlife 21

Figures 4-3 and 4-3A. Beaver dams can block emergency spillways causing water levels behind the dam to rise.

Figure 4-4. A lodge can reach 5-6 feet above the waterline.

Behavior: Beavers construct dams to create a depth of water 

suitable for them to hide from predators as they travel to 

their shore feeding grounds. Beaver use a variety of materials to construct these dams—the use of wood, fiber, metal, 

wire, and rocks is not uncommon. Beavers leave their lodge 

at dusk and spend most of the night working (removing 

shoreline trees, constructing dams, gathering food). However, in the fall season it is not uncommon to see a beaver 

working in the daytime as they gather food for the winter 

(Benyus, 1989). 

Field Tip: Perhaps the best indication of beaver is their dams. 

Dams are typically a few feet long, but can be up to several 

hundreds of feet long. A second indication is the presence of 

canals, which beaver build in the water to help them transport the trees they fell to construct the dams. Gnaw marks 

in a circular pattern on tree trunks are also good indicators 

of beaver, and trees cut by beavers show a distinctive tapered 

cone at the end of the trunk. An audible sign of beaver is the 

loud slap of their horizontally flattened tail on the surface of 

the water to alert other beaver to the presence of predators 

(Benyus, 1989).

The ranges for beaver, 

nutria and muskrat overlap, 

and their damages can 

appear similar. Careful 

examination of the 

damage, burrows, and 

proper use of the field 

tips listed in this manual 

will assist in accurate 

species identification 

and management. 
22 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

food

drying den

nest

waste den

Figure 4-5. The mountain beaver only leaves its den to forage or create new dens.

4.2.3 Mountain Beaver Overview

Mountain Beaver (Aplondontia rufa) is typically found in 

Washington, Oregon, and portions of California. Mountain beaver 

neither prefer mountainous habitat nor are true beavers. These rodents 

have short, heavy bodies and are dark brown above and lighter 

brown below; they resemble a tailless muskrat. Mountain beavers 

have long, strong claws, which they use to create burrows up to 19 

inches in diameter in wet soil near dense water-side vegetation.

Threat to Dams: Mountain beavers divert waterflow by blocking water with vegetation. The shallow location of the 

extensive burrows will often cause the ground to cave in. 

The mountain beaver’s activities could result in hydraulic 

alteration and structural losses.

Habitat and Home: Mountain beavers prefer habitats in forested areas where the canopy is open enough to allow dense 

understory vegetation. If a dam is covered with trees and 

thick understory, then a mountain beaver will likely find 

a comfortable habitat. Within this area, mountain beaver 

prefer moist gullies, and vegetated hillsides or flat areas that 

are not prone to flooding. Habitats dominated by red alder, 

salmonberry, huckleberry, and bracken and sword ferns are 

preferred by the mountain beaver. Mountain beavers dig extensive burrows that can cover a quarter-acre, are usually located near vegetative cover, and are generally 1-6 feet deep 

with 10-30 open entrances. The burrows contain deep (1-9 

feet) nesting and food chambers usually located about 3 feet 

below ground surface; the chambers can be large, usually 

measuring 2 feet in height and 2 feet in diameter. Mountain 

beavers do not like their burrows to be wet and will leave a 

burrow once it is flooded (University of Nebraska, 1994) 

(Figure 4-5).
Chapter 4. Overview and Identification of Nuisance Wildlife 23

walking

forefoot

hindfoot

Range of the mountain beaver in North America.

Food Habits: Mountain beavers are herbivores and eat any 

type of succulent vegetation, with sword fern and bracken 

fern being favorites (University of Nebraska, 1994). Mountain beavers will also girdle the base of trees and feed on 

small stems (Figure 4-6). Plants that are gathered by the 

mountain beaver are often dried near the burrow and are 

probably used for storage or nesting material. Mountain 

beavers dry their food by stacking vegetation on a nearby 

log or rock, which is termed “haystacking” (Figure 4-7). 

Mountain beaver usually feed on plants located within 50 

feet of their burrows (University of Nebraska, 1994). 

The identifying characteristic of a mountain beaver track is a front foot 

print that has a square heel and a hind print that displays a tapered heel.

Figure 4-6. Mountain beavers girdle trees and feed on small stems.

Figure 4-7. Mountain beavers dry their vegetation on 

logs, known as “haystacking,” before moving it into their 

burrows. Haystacks can be up to 2 feet high.
24 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

Figure 4-8. Ferns and Douglas fir branches placed in a 

burrow is a reliable field sign of mountain beaver. 

Behavior: Mountain beavers are nocturnal animals. They are 

superb diggers and spend much of the night digging and 

maintaining their labyrinth of burrows. Mountain beavers 

often stack cut vegetation in a burrow entrance, presumably 

to lower the vegetation’s moisture content before storing it 

in the burrow (University of Nebraska, 1994).

Field Tip: Stem and branch cutting within the vicinity of the 

dam may be a positive sign of mountain beavers. Signs of 

mountain beaver include freshly dug soil and chewed vegetation in proximity to a 6 to 8-inch diameter hole. Look 

for haystacks near the burrow entrance and vegetation piled 

in the burrow entrance (Figure 4-8).

4.2.4 Groundhog Overview

Groundhog (Marmota monax) (also known as Woodchuck or Rockchuck) 

are large burrowing rodents that weigh an average of 5 to 10 pounds 

and have an average body length of 16-20 inches. Groundhogs are 

usually grizzled brownish gray, although white and black individuals may 

occasionally be found. The groundhog’s forefeet have long, curved claws that 

are well adapted to digging burrows (University of Nebraska, 1994).

Threat to Dams: Groundhog burrows in earthen dams can 

weaken the embankment and act as a pathway for seepage.

Habitat and Home: The groundhog generally prefers open 

farmland and woody or brushy areas adjacent to open land. 

Groundhog burrows are usually located in fields or near 

grassy pastures or meadows, along fence rows, stone walls, 

roadsides, and near building foundations or the bases of 

trees (University of Nebraska, 1994) (Figure 4-9, shown 

on page 31). Groundhogs will burrow into earthen dams, 

generally on the downstream side of the dam, as this environment can be similar to their preferred habitat (Michigan 

State University Extension, 1998). Their burrows can be distinguished by the large mound of excavated earth deposited 

by the main entrance. Two or more entrances generally exist 

for each burrow system. Burrows are often well-hidden and 

may be difficult to locate.
Chapter 4. Overview and Identification of Nuisance Wildlife 25

walking

forefoot hindfoot

It may be difficult to tell the front and back tracks apart because when 

a groundhog walks, it puts its hind foot in the track of its front foot. 

Food Habits: Groundhogs are strict herbivores. They feed on a 

variety of vegetables, grasses, and legumes, including beans, 

peas, carrot tops, alfalfa, and clover. Groundhogs prefer to 

feed in the early morning and evening hours (University of 

Nebraska, 1994). 

Behavior: Groundhogs are usually only active during the day. 

During warm periods, they can often be found basking in 

the sun near their burrows. Groundhogs are one of the few 

mammals that enter a true hibernation period. Hibernation 

generally occurs from late October or early November to 

late February or March, although the exact timing depends 

on the latitude (University of Nebraska, 1994). New burrow construction occurs in late summer (USFS, 1994).

Field Tip: When approached or startled, a groundhog will 

often emit a shrill whistle followed by a low, rapid warble 

(University of Nebraska, 1994). An indicative sign of a 

groundhog burrow is the spring cleaning performed by the 

groundhog, which results in a mound of fresh dirt outside the burrow entrance. Adjacent trees may be girdled or 

clawed (Indiana Department of Natural Resources, 2003). 

Range of the groundhog in the North America. Look for burrow construction in the late summer months.
26 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

4.2.5 Pocket Gopher Overview

Pocket gophers are 

considered a significant 

dam safety issue in 23% 

of the surveyed states.

crest

phreatic surface

 Figure 4-9. Groundhog burrows are extensive and irregular in pattern. 

Pocket Gopher (Geomys spp., Thomomys spp., and Pappogeomys castanops) 

are medium-sized burrowing rodents that weigh an average of 3 to 20 

ounces and have an average body length of 5 to 14 inches. Their fine 

fur is highly variable in color, ranging from nearly black to pale brown 

to almost white. Pocket gophers have fur-lined pouches outside of the 

mouth that are used for carrying food. They have yellowish-colored 

incisor teeth that are always exposed, even when the mouth is closed.

Threat to Dams: Pocket gophers are generally only a threat 

to small earthen dams. They dig burrows that can lead to 

internal erosion and structural integrity losses in the dam. 

The presence of pocket gophers also increases the likelihood 

of badger activity. Badgers are one of the primary predators 

of pocket gophers. Badgers will attempt to dig gophers out 

of their burrows, which can be very destructive to earthen 

dams (See Chapter 4.2.6 for a discussion on badgers). 

Pocket gophers can also damage underground utilities, such 

as irrigation pipes or electric cables (USDA, 1991). 

Habitat and Home: There are 10 species of pocket gopher 

with substantial populations in the United States, but only 

one species is typically found in an area (USFS, 1994). They 

can occupy a wide range of habitats, from low coastal areas 
Chapter 4. Overview and Identification of Nuisance Wildlife 27

to mountains (USDA, 1991). Horseshoe-, fan- or kidneyshaped mounds of soil are characteristic evidence of pocket 

gopher burrows. Their burrows are nearly always kept 

closed with an earthen plug (University of Nebraska, 1994) 

(Figure 4-10). 

Food Habits: Pocket gophers are strict herbivores, eating 

all types of forbs, grasses, shrubs, and trees. Roots are the 

major food source, although during the growing season, 

pocket gophers will also eat the above-ground portions of 

plants (University of Nebraska, 1994). 

Behavior: Pocket gophers are solitary animals that spend 

much of their time underground. There is typically only one 

gopher per burrow, except during breeding season (USDA, 

1991). 

Plains (Geomys bursarius), and Botta (Thomomys botta) Pocket Gophers

Range of the pocket gopher in North America.

Northern (Thomomys talpoides), and Yellow-Faced 

(Pappogeomys castanops) Pocket Gophers

Southeastern (Geomys pinetis), and Southern 

(Thomomys umbrinus) Pocket Gophers
28 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

Field Tip: Pocket gopher activity can be distinguished from 

that of other burrowing animals by their burrow characteristics, particularly the fan-shaped mounds of soil and 

plugged burrow entrances. Pocket gophers will tunnel 

through the snow, pushing soil from below ground into 

the snow tunnels. When the snow melts, the soil “casts” or 

tubes can be found on the ground surface (USFS, 1994). 

Horseshoe-shaped mounds of soil are created in summer or 

late fall.

Pocket gopher tracks will show five toes on the hindfoot and four toes on 

the slightly smaller forefoot. Claw marks are usually well-defined.

Figure 4-10. Lateral burrows of the pocket gopher end in a soil mound or a soil plug. 

gopher mound

plug

plug

gopher tunnel and mound

walking

forefoot

hindfoot
Chapter 4. Overview and Identification of Nuisance Wildlife 29

4.2.6 North American Badger Overview

Badgers are considered 

a significant dam 

safety issue in 17% of 

the surveyed states.

The North American Badger (Taxidea taxus) is a stocky animal that can 

grow up to 30 inches long. It has grayish yellow fur with pale underparts, 

long claws, a short, bushy tail, and black feet. Badgers can weigh from 

19 to 30 pounds and can be identified by a white stripe that runs from 

its nose to the back of its head (University of Nebraska, 1994). 

Threat to Dams: Badgers are especially adapted for digging 

and dig in pursuit of prey and to construct dens for shelter. 

Badgers can cause severe damage to hydraulic structures. 

Badgers can exacerbate internal and external erosion in an 

earthen dam by enlarging existing burrows of prairie dog, 

pocket gopher, or ground squirrels, all of which can inhabit 

an earthen dam and are a preferred food of the badger. Badger dens create large voids in the earthen dam, compromising structural integrity.

Habitat and Home: Badgers prefer pastures or rangelands with 

light to moderate cover and few trees. Habitats with sandy 

or porous soils are preferred. Female badgers dig large burrows (5-30 feet long) with a large chamber 2-3 feet below 

the ground surface for birthing. Dens have one entrance that 

is usually elliptical in shape (University of Nebraska, 1994).

Food Habits: North American badgers are opportunist omnivores that feed on earthworms, mammals, birds, reptiles, 

grains, and fruits. Prairie dog, pocket gopher, and ground 

squirrels are common in badger diets. 
30 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

Behavior: Badgers are adept at pursuit and capture of grounddwelling prey. A typical burrow dug in pursuit of prey is 

shallow and about 1 foot in diameter (University of Nebraska, 1994). Badgers are mostly nocturnal but will be 

active during the day if the area is quiet. Badgers are usually 

solitary.

Field Tip: Large piles of dirt and rock left near animal burrows can indicate badger hunting activity. Badgers maintain 

the condition of their claws by sharpening them on trees or 

fence posts; claw marks can indicate badger presence (University of Nebraska, 1994). 

Badger tracks are similar to coyote tracks, but are distinct in 

the long claw marks on the front feet and the presence of five 

toes. Badger tracks are typically turned inward toward each 

other, and the hindprints are narrower than the foreprints.

walking

forefoot

hindfoot

Range of the badger in North America.

Badger tunnels and dirt 

mounds resulting from 

prey pursuit can cover an 

area the size of a car.
Chapter 4. Overview and Identification of Nuisance Wildlife 31

4.2.7 Nutria Overview

Look closely! Nutria are 

aquatic rodents often 

misidentified as either 

a muskrat or beaver. 

Nutria are considered 

a significant dam 

safety issue in 4% of 

the surveyed states.

Nutria (Myocastor coypus) With an average weight of 8 pounds and 

a body length of 24 inches (tail is an additional 16 inches long), 

nutria are larger than muskrat, but much smaller than beaver. With 

a preferred habitat that includes permanent water, nutria are excellent 

swimmers with webbed hind feet, but move awkwardly on land. 

Threat to Dams: Nutria construct extensive burrows as shelter 

in the upstream slope. Burrows can weaken an earthen dam 

to the point of collapse when soil becomes saturated by 

precipitation or high water, or when heavy vehicles cross 

the crest. Nutria are notorious for breaking through water-retaining levees in Louisiana and Texas (University of 

Nebraska, 1994).

Habitat and Home: Nutria can adapt to a variety of habitats, 

but prefer a semi-aquatic environment and particularly, the 

zone between land and permanent water. This zone is preferred for its abundance of aquatic vegetation. For the most 

part, any substantial nutria populations in the United States 

occur in freshwater marshes of coastal areas (University of 

Nebraska, 1994). Nutria are ground-dwellers during the 

summer, preferring to live in dense vegetation. The rest of 

the year nutria live in burrows they have dug, or that have 

been abandoned by armadillos, muskrat, or beaver. Nutria 

construct burrow entrances in vegetated banks of dams and 

waterways; a bank that has a slope greater than 45 degrees is 

a preferred location (University of Nebraska, 1994). Nutria 

burrows can be simple or complex; a complex burrow may 

have several tunnels and entrances at different levels in the 

bank. A burrow system will contain compartments (ranging 

from 1-3 feet across) for resting, feeding, and shelter from 

the weather and predators. Tunnels can be 4-6 feet in length.

In some cases, nutria 

tunnels have been so 

extensive that water flowed 

unobstructed through the 

embankment necessitating 

its complete reconstruction.
32 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

Tracks left by nutria may also have tail drag marks, or sometimes 

chest marks, as a nutria may drag its chest when on land. 

walking

forefoot

hindfoot

Food Habits: Nutria prefer aquatic plants such as sedges, 

rushes, cattails, and arrowheads, however the bark of black 

willow and bald-cypress may be eaten in the winter. Nutria 

eat food in a number of places including feeding platforms 

on the water (floating mats of vegetation or even on top of 

beaver and muskrat houses), in the water itself, or on land. 

Behavior: Nutria feed at night when food is plentiful, but will 

feed during the day if food is limited. Nutria can scratch or 

bite aggressively if captured or cornered.

Field Tip: Unlike muskrat or beaver, a nutria’s tail is round 

with scant hair, the whiskers are long (around 4 inches) 

and whitish, and nutria have prominent red-orange incisors. 

Trees girdled by nutria will show no teeth marks. 

Range of the nutria in North America. Nutria construct platforms 

of floating vegetation used 

for loafing, grooming, 

birthing, and escape, 

which are often mistaken 

for muskrat houses.
Chapter 4. Overview and Identification of Nuisance Wildlife 33

4.2.8 Prairie Dog Overview

Prairie Dogs (Cynomys spp.) are squirrel-like, burrowing rodents 

with squat, muscular bodies and short tails and ears. Their fur is 

sandy brown to cinnamon in color with grizzled black and buffcolored tips. Adult prairie dogs grow to a length of 13 to 17 inches 

and weigh approximately 2 to 4 pounds (USDA, 1991).

Threat to Dams: Prairie dogs dig burrows that can lead to 

internal erosion and structural integrity losses in earthen 

dams.

Habitat and Home: Prairie dogs prefer grassland or short shrubland habitats. They often establish colonies near intermittent streams or water impoundments (USDA, 1991). Prairie 

dog burrows are found in open areas with low vegetation. 

Their burrows are distinguished by relatively large holes 

and cone-shaped mounds. Prairie dogs remove the vegetation from around their burrows and use it for food or 

nesting material (USDA, 1991). Other animals often make 

their homes in prairie dog burrows, including the federally 

protected black-footed ferret and burrowing owl. 

Food Habits: Prairie dogs eat mostly grass, although they will 

also eat flowers, seeds, shoots, roots, and insects when available (University of Nebraska, 1994).

Behavior: Prairie dogs live in large colonies known as 

“towns.” Each town is made up of a complex series of tunnels and may have as many as 20 to 50 burrow entrances. 

Prairie dogs are social animals that are most active during 

the day (University of Nebraska, 1994). 

Field Tip: Look for mounds of earth about 1 to 2 feet high 

that resemble miniature volcanoes. 

Prairie dogs are considered 

a significant dam 

safety issue in 8% of 

the surveyed states.
34 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

Prairie dog tracks will show five toes on the hindfoot 

and four toes on the slightly smaller forefoot. 

walking

forefoot

hindfoot

Black-Tailed (Cynomys ludovicianus), and Gunnison 

(Cynomys gnnisoni) prairie dogs

Range of the prairie dog in North America.

White-Tailed (Cynomys leucurus), and Mexican 

(Cynomys mexicanus) prairie dogs
Chapter 4. Overview and Identification of Nuisance Wildlife 35

4.2.9 Ground Squirrel Overview

Columbian (Spermophilus columbianus), Franklin (Spermophilus 

franklinii), California (Spermophilus beecheyi), and 

Mexican (Spermophilus mexicanus), ground squirrels

Richardson (Spermophilus richardson), and Wyoming 

(Spermophilus elegans) ground squirrels

Range of the ground squirrel in North America.

Ground Squirrel (Spermophilus spp.) are small to medium-sized burrowing 

rodents. Twenty-three species of ground squirrels live in the United States 

(University of Nebraska, 1994). They vary is size, with lengths ranging 

from 6 to 20 inches and weight ranging from 0.25 to 2.5 pounds. They 

also vary in color, ranging from brown to reddish brown to gray. Some 

species have markings, such as spots or stripes. Some species have long 

bushy tails, while others have short tails with short hair (USDA, 1991).

Threat to Dam: Ground squirrels dig burrows that can lead to 

internal erosion and structural integrity losses in earthen 

dams. The presence of ground squirrels also increases the 

likelihood of badger activity. Badgers will pursue ground 

squirrels into their burrows, which can be very destructive 

to earthen dams (USDA, 1991). 

Habitat and Home: Ground squirrels can be found in at least 

27 states west of Ohio. They occupy a wide range of habitats 

from low coastal areas to mountains. Ground squirrels keep 

their burrows unplugged. Specific burrow design varies 

with species, soil type, habitat and climate. Some species 

of ground squirrels are colonial, which means that several 

individuals live in the same burrow system. These systems 

consist of clustered, above-ground mounds that resemble 

prairie dog burrows. They are generally easier to spot than 

the burrows of solitary ground squirrel species, which tend 

to be scattered and inconspicuous (USDA, 1991). 
36 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

Townsend (Spermophilus townsendi), Thirteen-lined 

(Spermophilus tridecemlineatus), and Round-tailed 

(Spermophilus tereticaudus) ground squirrels

Belding (Spermophilus beldingi) and Spotted 

(Spermophilus spilosoma) ground squirrels

Washington (Spermophilus washingtoni), Idaho (Spermophilus 

brunneus), and Uinta (Spermophilus armatus) ground squirrels

Rock (Spermophilus variegatus) ground squirrels

Range of the ground squirrel in North America (continued).
Chapter 4. Overview and Identification of Nuisance Wildlife 37

Although ground squirrel tracks will vary in size, they generally show five 

toes on the hindfoot and four toes on the smaller and rounder forefoot.

walking

forefoot

hindfoot

Food Habits: Ground squirrels mostly eat plant material, although some species may also eat insects, eggs, carrion, and 

other animal material (USDA, 1991).

Behavior: Ground squirrels are only active during the day, 

and they are most active during mid-morning and late 

afternoon. They hibernate in the winter, and most species 

estivate in summer as well (USDA, 1991). 

Field Tip: During warm months, ground squirrels are quite 

active during the day and can be easily spotted. Unplugged 

burrows are a distinctive characteristic of ground squirrel 

inhabitation (USDA, 1991).

4.2.10 Armadillo Overview

Ground squirrels are 

considered a significant 

dam safety issue in 15% 

of the surveyed states.

The Armadillo (Dasypus novemcinctus) is a medium-sized animal, 

about 8 to 17 pounds, with a protective, armor-like shell on its head, 

body, and tail. It has nine movable bands across its back, and the tail is 

covered with a series of overlapping rings. The armadillo has a small head 

with a long, narrow, piglike snout (University of Nebraska, 1994). 

Threat to Dams: Armadillos dig burrows that can result in 

internal erosion and structural integrity losses in dams.

Habitat and Home: It prefers forest, woodland and brush 

habitat, as well as areas near creeks and rivers. The armadillo 

will also inhabit areas with rocks, cracks, and crevices that 

are suitable for burrows (University of Nebraska, 1994). 

Armadillos generally dig burrows 7 to 8 inches in diameter 

and up to 15 feet in length. They can be found in rock piles, 

around stumps, brush piles, or terraces around brush or 

dense woodlands. Armadillos usually have more than one 

den in an area (University of Nebraska, 1994). 
38 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

Armadillos have four toes on their forefeet and five toes 

on their hindfeet, although not all toes may show up in 

their tracks. Sharp claw marks are often visible.

walking

forefoot

hindfoot

Food Habits: The armadillo primarily eats insects and their 

larvae. They also feed on spiders, earthworms, scorpions, 

and other invertebrates. To a lesser extent, they may eat some 

fruit and vegetable matter (University of Nebraska, 1994). 

Range of the armadillo in North America.

Armadillos are considered 

a significant dam 

safety issue in 4% of 

the surveyed states.

Behavior: During the summer, the armadillo is active from 

twilight through early morning hours, but in the winter, it 

is usually only active during the day. The armadillo has poor 

eyesight, but a keen sense of smell. It can run fast when in 

danger and is also a good swimmer (USDA, 1991). 

Field Tip: Characteristic signs of armadillo activity are shallow 

holes, about 1 to 3 inches deep and 3 to 5 inches wide, dug 

in search of food (University of Nebraska, 1994).
Chapter 4. Overview and Identification of Nuisance Wildlife 39

4.2.11 Livestock Overview

Livestock are considered 

a significant dam 

safety issue in 25% of 

the surveyed states.

Livestock can include cattle, horses, sheep, goats, and pigs of all varieties, 

domesticated and wild. Livestock exist widely across the United States 

and utilize earthen dams and farm ponds for grazing and drinking. 

Threat to Dams: Livestock can damage an earthen dam by 

removing stabilizing vegetation through grazing, trampling, 

and rooting. External erosion can occur without vegetative 

cover, and erosion pathways can be created as livestock traverse the embankment (Figures 4-11 and 4-12). Damages 

are most severe in arid regions, and damage is often not 

noted until the wet season when precipitation collects in 

holes and along erosion pathways. Livestock carcasses could 

alter or block water flow if located at control structures. 

Wild pigs commonly damage farm ponds and can cause 

substantial damage to a grassy area in a single night (University of Nebraska, 1994).

Habitat and Home: Livestock can occur anywhere in the 

United States. In some cases, several livestock species will 

graze in one area. Wild pigs can exist in a variety of habitats 

but prefer dense brush or marsh vegetation as cover. Wild 

pigs are often found inhabiting livestock-producing areas 

(University of Nebraska, 1994).

Food Habits: Most livestock, including cows, sheep, goats, and 

horses, are grazers. Pigs, however, generally root for underground vegetation, in addition to feeding on acorns and 
40 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

other mast. Livestock disturb soil and vegetation through 

their feeding methods. 

Behavior: Location to a water source is considered the primary influence on livestock’s activity within a given grazing area, followed by desirable forage and topography of 

the grazing area. In hot weather, pigs will wallow in ponds, 

springs, or streams that contain or are near vegetative cover. 

Field Tip: Livestock are easily identified as they are often 

intentionally grazed on lands near farm dams. Wild pigs are 

obvious if observed, otherwise look for wallows. 

One milk-producing Jersey cow can 

drink up to 12 gallons of water a day. 

Herds of dairy cows typically include 

50 to 100 animals. That’s a lot of 

hoof-traffic at an earthen dam!

Range of livestock, and wild pigs in North America.

Tracks can be used to identify wild pigs. Tracks are generally 

not needed to identify other types of livestock since they are 

often intentionally grazed on lands near farm dams. 

walking

forefoot

hindfoot

Figure 4-11. Livestock can cause external erosion by 

creating ruts and erosion paths via hoof traffic.

Figure 4-12. Livestock can remove stabilizing 

vegetation through grazing and hoof traffic.
Chapter 4. Overview and Identification of Nuisance Wildlife 41

4.2.12 Crayfish Overview

Crayfish are considered 

a significant dam 

safety issue in 4% of 

the surveyed states.

Figure 4-13. A crayfish burrow is a cone-shaped mound or “chimney” made with mud pellets.

Crayfish (Cambarus spp.) resemble miniature lobsters. There 

are over 300 species of various sizes, shapes, and colors in 

the United States (University of Nebraska, 1994). 

Threat to Dams: Crayfish burrow into earthen dam embankments; extensive burrowing may cause internal erosion and 

structural integrity losses. 

Habitat and Home: Crayfish are found in a variety of fresh water habitats, including streams, rivers, ponds, lakes, swamps, 

and wet meadows (Peckarsky et al, 1990). Crayfish burrows 

are usually located along the shoreline close to the water’s 

edge. They may be anywhere from a few inches to three 

feet deep. The opening is generally about 1⁄4 to 2 inches in 

diameter with a cone-shaped mound, known as a “chimney,” plugging the burrow (Virginia Cooperative Extension, 

2001a) (Figure 4-13).

Food Habits: Crayfish eat both living and dead plant and animal material. Almost half of their diet consists of bottomdwelling worms and insects. The rest of their diet consists of 
42 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

living and decaying aquatic vegetation (Virginia Cooperative 

Extension, 2001a).

Behavior: A crayfish will molt several times in its short lifespan. They can be quite aggressive towards each other and 

toward anything they perceive as a threat (Peckarsky et al, 

1990). Most crayfish dig burrows to use as a refuge from 

predators and as a resting place during molting and inactive 

periods (Virginia Cooperative Extension, 2001a). 

Field Tip: Crayfish stay in their burrows or in mud bottoms 

during cold weather. They will emerge, and be easier to 

spot, once the water warms up (Virginia Cooperative Extension, 2001a). 

Range of the crayfish in North America.

4.2.13 Coyote Overview

Coyote are considered 

a significant dam 

safety issue in 4% of 

the surveyed states.

The Coyote (Canis latrans) is a member of the dog family, and in size 

and shape, it resembles a small German shepherd, with erect pointed 

ears, slender muzzle, and a bushy tail. Coyotes are generally brownishgray with a lighter colored belly, although this varies widely across local 

populations. In the west, adult males typically weigh 25 to 45 pounds 

and adult females typically weigh 22 to 35 pounds. Coyotes in the east 

are usually larger, with adult males weighing about 45 pounds and adult 

females weighing about 30 pounds (University of Nebraska, 1994).

Threat to Dams: Although coyotes do not pose a large threat 

to earthen dams, den construction or enlargement, and 

digging out prey that live at the dam can cause structural 

integrity losses.

Habitat and Home: Coyotes exist in virtually any type of habitat, arctic to tropic. High densities of coyotes even appear in 

the suburbs of major western cities such as Los Angeles and 

Phoenix. Their dens are often found in steep banks, rock 

crevices, sinkholes, and underbrush, as well as open areas. 

Dens are usually located close to water. Coyotes will often 

dig out and enlarge burrows of other animals. Size of coyote 

dens varies from a few feet to 50 feet, and each den often 

has several openings (University of Nebraska, 1994).
Chapter 4. Overview and Identification of Nuisance Wildlife 43

Badger tracks are often confused with coyote tracks, but note that 

coyotes only have four toes on each foot, while badgers have five toes. 

walking

forefoot

hindfoot

Food Habits: Coyotes eat a variety of animals, insects, fruits, 

and vegetables (University of Nebraska, 1994).

Behavior: During hot summer months, coyotes are most active at night and during the early morning hours. During 

cooler weather, and in areas with minimal human activity, 

coyotes may be active throughout the day. Coyotes have 

good eyesight and hearing and a keen sense of smell. Their 

adaptable behavior and social system allows them to survive, 

and even flourish, in the presence of humans (University of 

Nebraska, 1994).

Field Tip: Coyotes can often be identified by their tracks, 

although it should be noted that regular dog tracks are often 

mistaken for coyote tracks. Coyote dens are often located in 

the downstream slope. 

Range of the coyote in North America.
44 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

4.2.14 Moles and Voles Overview

Moles and voles are 

considered a significant 

dam safety issue in 10% 

of the surveyed states.

Moles (Scapanus spp.) are small insectivores that are often confused with 

voles, shrews, and pocket gophers. Moles, however, can be distinguished 

by their hairless, pointed snout, small eyes, and webbed forefeet. There 

are seven different species of moles living in the United States. Adult 

males grow to a length of about 7 inches and weigh about 4 ounces; 

adult females are slightly smaller (University of Nebraska, 1994). 

Voles (Microtus spp.) also known as meadow mice or field mice, are 

compact rodents with short legs and short tails. There are 23 species of 

voles in the United States. Most are gray or brown, and about 4 to 8 

inches long; although both size and coloration varies across species. 

Threat to Dams: Earthen dams may provide good hunting 

grounds for moles. Although they usually make their home 

burrows in dry, upland areas, they prefer to hunt in areas 

that are cool and moist. They construct tunnels from their 

dens to their hunting grounds. If located in an earthen 

dam, these tunnels may cause internal erosion and structural integrity losses. When present in large numbers, voles 

may also cause damage to earthen dams. They dig extensive 

burrow systems that could lead to internal erosion and 

structural integrity losses in the dam (University of Nebraska,1994).

Habitat and Home: Moles can be found across most of the 

United States. As mentioned above, they generally construct 

their burrows in dry, upland areas. Deep runways connect 

their dens to their hunting grounds (University of Nebraska, 1994) (Figures 4-14 and 4-15, shown on page 51). 

Voles can also be found across most of the United States. 

They prefer areas of heavy ground cover, although they can 

survive in a wide variety of habitats. Burrow systems consist 

of a series of tunnels and surface runways, and often have 

several entrances (University of Nebraska, 1994) (Figure 

4-16, shown on page 51).

Food Habits: Moles primarily eat insects, grubs, and worms. 

Voles are mostly herbivorous, primarily eating grasses and 

forbs. Voles will also occasionally eat snails, insects, or animal remains (University of Nebraska, 1994).
Chapter 4. Overview and Identification of Nuisance Wildlife 45

Vole tracks.

walking

forefoot

hindfoot

Range of the mole in North America. Range of the vole in North America.

Behavior: Moles are solitary animals, and they spend most of 

their time underground. They are active through all seasons 

of the year. Voles are also active throughout the year, both 

day and night. They are excellent swimmers and often try 

to escape from predators through the water (University of 

Nebraska, 1994). 

Field Tip: Moles push up volcano-shaped mounds of soil 

when they are building tunnels. The mounds may be anywhere from 2 to 24 inches tall. Surface tunnels or ridges are 

also an indication of mole activity. Voles can be identified by 

their extensive surface runway systems. These runways are 

generally 1 to 2 inches in width. 
46 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

mole hill mole ridges

entrance to 

underground 

runway system

Figure 4-16. Voles are most easily identified by an extensive surface runway system with many burrows.

Figure 4-14. Mole burrows form ridges visible from the surface.

Figure 4-15. Moles push dirt vertically to the surface, which forms a mound.
Chapter 4. Overview and Identification of Nuisance Wildlife 47

4.2.15 River Otter Overview

River otters are considered 

a significant dam 

safety issue in 4% of 

the surveyed states.

The River Otter’s (Lutra canadensis) sleek body, short legs, webbed 

toes, and tapered tail help it thrive in its aquatic environment. 

Otter fur is thick and shaded from brown to near black on most 

of the body, with a lighter brown to beige on the belly, chin, 

throat, cheeks, and chest (University of Nebraska, 1994). 

Threat to Dams: Otters sometimes dig bank dens for shelter 

with an underwater entrance for use in the winter and 

an above-water entrance for use in the summer (Benyus, 

1989). Dens can cause large voids in the dam embankment, 

and underwater entrances provide pathways for internal 

erosion and wave action if water levels rise into the embankment den. 

Habitat and Home: Otters are associated almost invariably with 

water environments no matter the water type: fresh, brackish, or salt. Water quality, available fish forage, and available 

den sites are the most important factors in determining 

otter habitat. Otters can be found in lakes, rivers, streams, 

bays, estuaries and associated riparian habitat. Otters most 

often utilize existing bank dens and lodges constructed by 

beaver, muskrat, and nutria. Otherwise, otters use hollow 

logs and rock crevices as their shelter and construct natal 

dens on small streams that lead to major drainages (University of Nebraska, 1994).

Food Habits: Otters prefer fish of several varieties, but also 

feed on shellfish, crayfish, reptiles, and amphibians. 

Behavior: Otters spend most of the day feeding and participating in group play. Otters are superb swimmers and very 

alert.

Field Tip: Look for slides into the water or snowbank (in 

winter) where otters play. Look for “haul-outs,” worn areas 

along the bank where otters consistently pull themselves out 

of the water. If this area is indeed a haul-out, there will be a 

trail leading away from the haul-out to a patch of trampled 

vegetation where otters roll around to dry themselves after 

a swim or to leave their scent (Benyus, 1989). Listen for the 

blow and sniff sounds of a surfacing otter.
48 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

4.2.16 Gopher Tortoise Overview

Tortoises are considered 

a significant dam 

safety issue in 4% of 

the surveyed states.

The inner toe of the otter’s hind paw juts out to the side.

walking

forefoot

hindfoot

Range of the river otter in North America.

Gopher Tortoise (Gopherus polyphemus) are large, terrestrial tortoises 

with a shell length of 10 to 15 inches that weigh about 9 pounds. The 

gopher tortoise is a protected species and a permit is always required to 

possess, study, remove, or relocate a specimen (Gopher Tortoise Council, 

2001). The burrows of the gopher tortoise are also protected by law. Over 

360 animal species have been documented inhabiting a gopher tortoise 

burrow so use caution when investigating a burrow. Many of the species 

which coexist in or use gopher tortoise burrows are also protected by 

state and federal laws, such as the burrowing owl and indigo snake. 

Threat to Dams: The gopher tortoise’s strong claws make it an 

effective burrower. Burrows can be 40 feet long and 10 feet 

deep and will include a spacious chamber used to cool off 

during the heat of the day (Gopher Tortoise Council, 2001). 

Gopher tortoise burrows can cause structural integrity 

losses. 
Chapter 4. Overview and Identification of Nuisance Wildlife 49

walking

Habitat and Home: Gopher tortoises prefer to dig their burrows in dry, upland habitats especially where saw-palmetto 

is present in the understory and sandy soils dominate. 

Gopher tortoises can live in grassy areas, pastures, and old 

fields as long as there are well-drained sandy soils, herbaceous plants, and sunny, open areas for nesting and basking 

(Gopher Tortoise Council, 2001). Look for burrows on the 

southeastern side of sandy hills (such as old dunes that are 

covered in vegetation) at a 30-degree angle from the surface 

(Benyus, 1989; Enchanted Forest Nature Sanctuary, 2003). 

The burrow entrance, or “apron,” will be marked by a characteristic mound of loose sand. The downstream slope and 

toe of a dam may be suitable for gopher tortoises, as might 

a forest fringe in a dam area.

Note: In some cases, snapping turtles may hibernate or 

lay eggs in an existing muskrat den and as such, are often 

identified as the responsible burrowing animal. In truth, 

turtles are more correctly simply associated with burrowing 

animals, rather than responsible for burrows. Depending on 

its size, the snapping turtle may enlarge an existing muskrat 

den. 

Range of the gopher tortoise in the United States.

The shell of the gopher tortoise may obliterate some of the track as it drags.

An east-central Florida 

study indicates that a male 

gopher tortoise constructs 

and uses an average of 

17 burrows. Some males 

construct and use as 

many as 35 burrows.

Food Habits: Primary food sources of the gopher tortoise 

include low-growing grasses, herbs, and berries. 

Behavior: Gopher tortoises emerge from their burrows in the 

morning to feed and return to the burrows if temperatures 

get too hot or cold. 

Field Tip: Look for large mounds of loose sand created as the 

gopher tortoise digs its burrow. 
50 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

Fox are considered a 

significant dam safety 

issue in 4% of the 

surveyed states.

4.2.17 Red Fox and Gray Fox Overview

The Red Fox (Vulpes vulpes) is dog-like in appearance with large pointed 

ears and an elongated pointed muzzle. It typically has a light orange-red 

coat with lighter colored underfur, black legs, and a white-tipped tail. Coat 

coloration can vary from red to gray to black, but the tail tip is always 

white. Adult red foxes can weigh anywhere from 7.7 to 15.4 pounds; males 

are about 2.2 pounds heavier than females (University of Nebraska, 1994). The Gray Fox (Urocyon cinereoargenteus) has a long, bushy tail with 

a black tip. It is salt-and-pepper gray over most of its body, with some 

rusty yellow spots on the sides of the neck, back of the ears, legs and feet. 

Adult gray foxes weigh about 7 to 13 pounds, and measure about 32 to 

45 inches from nose to tip of tail (University of Nebraska, 1994).
Chapter 4. Overview and Identification of Nuisance Wildlife 51

Range of the red fox in the North America.

Range of the gray fox in North America.

Threat to Dams: Foxes do not pose a great threat to earthen 

dams. It is possible that they could cause damage by digging out burrowing animals for food. This type of damage 

may be prevented with good rodent control and vegetative 

management.

Habitat and Home: The red fox prefers open country with 

moderate cover, although it is generally adaptable to any 

habitat within its range. Red foxes are commonly found 

in urban areas. They may either dig their own dens or use 

abandoned groundhog or badger burrows. The gray fox 

prefers areas of dense cover such as swamp land or thickets. 

Gray foxes can also be found in urban areas. They commonly use wood piles, rocky outcrops, or hollow trees as den 

sites (University of Nebraska, 1994). 

Food Habits: Foxes mostly eat rabbits, mice, bird eggs, insects, 

and fruit (University of Nebraska, 1994). 

Behavior: Foxes are solitary animals that are most active during twilight and early morning hours. They have a variety of 

calls that sound like barks, screams, howls, yaps, growls, and 

hiccups (University of Nebraska, 1994).
52 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

Tracks of red fox.

walking

forefoot

hindfoot

Canada geese can cause 

erosion from overgrazing similar to that 

caused by livestock. 

The Canada Goose (Branta canadensis) is a large bird that grows to a 

height of 2 to 3 feet and weighs approximately 10 to 12 pounds. It has a 

grayish-brown body and wings; black feet, bill and neck; a white underside; 

and a white patch on each cheek (USDA, 2003). There are 11 subspecies 

that live in the United States (Virginia Cooperative Extension, 2001b). 

Field Tip: Fox dens may be identified by several 10-inch wide 

entrance holes, with sandy aprons of soil spilling from them 

(Benyus, 1989).

4.2.18 Canada Goose Overview

Tracks of gray fox.

walking

forefoot

hindfoot

Threat to Dam: Canada geese build their nests near water. If 

they choose to nest on or near an earthen dam, their nesting 

and feeding activities could cause external erosion. 

Habitat and Home: Canada geese are found across the United 

States. Many Canada geese spend their summers in Canada 

and migrate south to the United States during the winter. 

Some geese, known as resident Canada geese, spend most 

of the year in the same general area and fly only far enough 

to find food or open water (Virginia Cooperative Extension, 

2001b). Canada geese nest in areas near open water, such 

as swamps, marshes, meadows and lakes. Nests are typi-
Chapter 4. Overview and Identification of Nuisance Wildlife 53

Tracks of the Canada goose.

gait

Range of the Canada goose in North America.

cally made from weeds, twigs, grass, moss, and pine needles 

(University of Michigan Museum of Zoology, 2002). 

Food Habits: Canada geese eat a variety of grasses and aquatic 

plants. They will also eat crops such as corn, soybeans, and 

wheat. Young Canada geese require more protein, and will 

consequently eat insects, small crustaceans, and mollusks 

(Virginia Cooperative Extension, 2001b). 

Behavior: Canada geese are social animals that communicate 

to each other through a series of calls. They tend to be aggressive birds, particularly the males. They will vigorously 

defend their territory, nests, and eggs from intruders (University of Michigan Museum of Zoology, 2002). 

Field Tip: Canada geese can be easily identified by the white 

patches on their cheeks. In absence of the birds themselves, 

Canada geese can be identified by their long, black, cylindrical droppings.
54 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

4.2.19 American Alligator Overview

Alligators are considered 

a significant dam 

safety issue in 2% of 

the surveyed states.

The American Alligator (Alligator mississippiensis) is one of the largest 

animals in North America. Adult males can grow to a length of 14 feet 

and weight up to 1,000 pounds. Adult females can grow to a length of 10 

feet and weigh up to 250 pounds. They have a rounded snout and black 

and yellow-white coloration (University of Nebraska, 1994). Alligator 

hunting is allowed in several states under strict quota or licence guidelines.

Threat to Dam: Alligators sometimes dig burrows or dens 

for refuge from cold temperatures, drought, and predators. 

These burrows can cause internal erosion and structural 

integrity losses in earthen dams (University of Nebraska, 

1994).

Habitat and Home: Alligators can be found in almost any 

type of fresh water, including wetlands, lakes, canals, and 

streams. They will occasionally inhabit brackish or salt water 

environments (University of Nebraska, 1994).

Food Habits: Alligators will prey upon whatever creatures are 

most available, including fish, turtles, birds, mammals, and 

other alligators. Alligators are opportunistic feeders and will 

eat carrion if it is available and they are sufficiently hungry. 

If they are near human environments, they may also eat pets 

and livestock (University of Nebraska, 1994).
Chapter 4. Overview and Identification of Nuisance Wildlife 55

4.2.20 Ants Overview

Ants are considered a 

significant dam safety 

issue in 4% of the 

surveyed states.

Range of the American alligator in North America.

Behavior: Because they are cold-blooded, alligators are most 

active when the temperature is warm. When the temperature drops below 700

F, alligators will stop feeding, and 

when the temperature drops below 550F, they become 

dormant. Alligators are not typically aggressive toward humans, but they can and will attack if provoked (University 

of Nebraska, 1994). 

Field Tip: Alligators are large animals, but they blend into 

their surroundings. It is important to be vigilant and cautious around any water body in the alligator’s range. 

Ants (Formicidae spp.) are small insects that live in large colonies. The 

body of an ant is clearly divided into three sections. Many different species 

of ants live in the United States. Color and size varies widely across 

species (University of Florida Cooperative Extension Service, 2002). 

Threat to Dam: Ants often build their homes underground. 

Their colonies consist of a complex series of tunnels that 

excacerbate existing cracks and can “soften” the embankment, threatening the structural integrity of an earthen dam.

Habitat and Home: Ants can be found across the United States 

in a variety of habitats. Most ants live in the soil, although 

some also live in wood or in the cavities of plants (University of Arizona, 1997). 
56 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

Food Habits: Ants eat a variety of foods, including plants, sugars, seeds, and small insects (University of Florida Cooperative Extension Service, 2002). 

Behavior: Ants are social animals. They live in colonies comprised of one or a few queens and many workers. Some ants 

have a potent sting (University of Arizona, 1997).

Field Tip: Small mounds of soil are often indicative of ant 

inhabitation. 

Range of the ant in North America.
Chapter 5. Dam Repair and Intrusion Prevention Through Design 57

5.0 Dam Repair And Intrusion 

Prevention Through Design 

Once the inspection is completed according to the guidelines (refer to Chapter 3.0) and considering the biological 

perspectives presented in Chapter 4.0, the dam specialist 

will need to take action relative to damages found at the 

dam. Specifically, the dam owner will need to repair burrow 

or beaver dam damage, and determine the appropriate level 

and type of prevention action (e.g., reinforced concrete wall 

and slab system on upstream slope to prevent muskrat burrows). This Chapter first outlines burrow repair procedures, 

followed by a discussion of each earthen dam zone (which 

corresponds to the zones described in Chapter 3.3 of this 

manual) with regard to the relative priority of prevention 

action for each zone. Lastly, design options to mitigate and 

prevent future animal intrusions are presented for each 

wildlife species. The prevention methods in this chapter 

relate to modification of the dam or its structures; a discussion of prevention through animal control methods (e.g., 

trapping) is presented in Chapter 6.0. 

The majority of the prevention action design criteria of this 

Chapter are meant to be incorporated when major features 

of the dam can be easily altered such as during new dam 

construction or dam repair construction, when the majority 

of the dam or a large portion of the dam will be reworked. 

The input of a professional engineer is required to ensure 

proper design and construction of prevention actions. 

5.1 Conformity to the Clean Water Act of 1972

The Clean Water Act of 1972 (CWA) is the primary guidance for protecting surface water quality in the United 

States. The goals of the CWA are to restore and maintain the 

chemical, physical, and biological integrity of the nation’s 

waters so that they can support “the protection and propagation of fish, shellfish, and wildlife and recreation in and 

on the water.” Towards these goals, the CWA sets water quality standards for waterbodies, which are upheld by antidegradation policies and programs, ambient monitoring, and 

pollutant load reduction strategies as necessary. 

In the dam environment, extensive vegetation removal, burrow excavation and repair, and dam restoration measures 

could trigger the CWA if dredged or fill materials could 

be deposited into wetlands or Waters of the United States. 

As such, all remediation activities must be completed in 

accordance with the CWA and its provisions, and coordination with the State Dam Safety Official and the State Water 

Resources Agency is required.
58 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

5.2 The Role of Vegetation Management

Proper vegetation management is a cornerstone of effective 

wildlife intrusion management. In most cases, wildlife will 

not inhabit an earthen dam that does not provide vegetation for food supply, protective cover, or shelter. If a variety 

of vegetation exists at the dam, then wildlife will choose 

to inhabit the earthen dam environment over other areas 

lacking in vegetation or without a water supply. Ideally, the 

earthen dam environment will contain appropriate grass 

species maintained such that dam inspections can be conducted easily without visual obstruction of the embankment 

and other appurtenant structures. Vegetation such as dense 

groundcover and thick, woody trees and shrubs not only 

hinder dam inspections, but can also obscure indicators of 

potential performance problems such as animal burrows, 

settlement, depressions, cracks, and similar issues. If vegetation is too thick, animal burrows can go undiscovered and 

proper animal intrusion mitigation may not occur. 

In general, it is advised to limit vegetation at the earthen 

dam to low-growing native grass that is mowed regularly, 

and to keep the embankment and spillway inlet and outlets 

free of vegetation. Vegetated emergency spillways should be 

maintained in a similar fashion as the dam embankment. 

Maintained grass will accommodate thorough inspections 

and limit the number of wildlife species that can easily 

inhabit the dam. If a dam contains vegetation other than 

appropriate grasses, then the dam owner should complete 

mitigation and management as outlined in the FEMA document, A Technical Manual on the Effects of Tree and Woody Vegetation Root 

Penetrations on the Safety of Earthen Dams (FEMA, 2002) and the 

FEMA brochure, Dam Owner’s Guide to Plant Intrusion of Earthen 

Dams (FEMA, 2003). 

5.3 Burrow Repair Procedures

Repair actions can be separated into two categories: restoration measures and preventive measures. As the names imply, 

restoration measures address repairing a deficiency, whereas 

preventive measures prevent or avert future damage in the 

area. Specific restoration and preventive measures applicable 

for various locations in the dam are discussed below.

5.3.1 Restoration Measures

Damage from animal intrusions can occur throughout the 

dam. The damage can include removal of surface vegetation, 

rutting, and burrowing. Regardless of the damage location, 

applicable restoration options depend upon the judged 

severity of the damage. 

Filling Ruts and Near Surface Deformation

Ruts, near surface deformation, and loss of vegetation can 

be the result of frequent animal crossings, most likely by 

livestock. Repair of these deficiencies is generally considered not critical. However, if left unattended for a sufficiently long period of time, these deficiencies can result 

in a progressive loss of vegetation and surface soils due to 

erosion. In extreme cases, the damage can lead to increasing 

amounts of erosion in localized areas, jeopardizing performance and requiring significant maintenance. Timely repair 

of ruts and vegetation loss can save considerable effort and 

expense later.

The repair methodology for ruts, surface deformation, and 

vegetation loss includes the following steps:

Fill the rut with soil of a similar type to that of the dam 

embankment. Overfill the rut slightly to account for 

compaction of the fill material. 

Compact the soil using hand held or walk behind equipment. In order to achieve reasonable compaction, the fill 

material should not contain particle sizes greater than 

1 inch in diameter. For larger ruts, and ruts created by 

vehicles, larger diameter material may be acceptable. The 

compacted surface should be smooth and level with the 

surrounding ground.

Revegetate the area with grass species appropriate for the 

region (see Chapter 5.2).

Filling Burrows

Methods for repairing or filling an animal burrow are essentially limited to two basic types. The first method considers filling the burrow without excavation while the second 

method considers excavating the burrow and backfilling the 

area. Details for each method are discussed below.

Observed burrows without signs of embankment distress 

(e.g., cracking, slumping) in the area may simply require 

filling with an impervious material or cementious grout. 

To fill the entire burrow, a process often referred to as 

“mud-packing” can be applied. This method consists of 

placing one or two lengths of metal stove or vent pipe vertically into the burrow. When the pipe is properly sealed, a 

slurry of 90% earth and 10% concrete, plus an appropriate 

amount of water to make the slurry flow, is placed in the 

pipe and allowed to flow into the burrow (Virginia Dam 

1.

2.

3.
Chapter 5. Dam Repair and Intrusion Prevention Through Design 59

A local dam safety 

professional should be 

notified prior to any 

excavation activities in 

an embankment dam.

Safety Program, 2003). The last 6 inches is filled with dirt 

that will support grass growth.

On the other hand, signs of embankment stress surrounding 

a burrow may indicate massive soil movement into the burrow. In these cases and at the owner’s discretion, complete 

removal of the burrow is preferred. Shovels or backhoes 

could be necessary during excavation depending upon the 

burrow location, size, and depth. Excavation limits will be 

defined by the burrow size and location as well as the density and type of embankment material. Prior to excavation, 

dam safety professionals and dam owners should examine 

potential consequences of soil removal, including slope 

instability and increased hydraulic gradient. The completed 

excavation should be thoroughly inspected for adequate 

removal of the animal burrow. Voids remaining from an 

animal burrow can develop into potential internal erosion 

pathways or sinkholes.

Once excavation is complete, the resulting hole must be 

properly backfilled in a timely manner. Acceptable backfill 

The final step is to revegetate the disturbed area. Native 

grass species appropriate for embankment dam slopes 

should be provided (see Chapter 5.2). 

5.3.2 Preventive Measures

For a specific animal intrusion or animal related deficiency, 

appropriate preventive measures are highly dependent on 

the affected area’s location on the dam. Therefore, common 

preventive measures are discussed in the context of the 

Repair Zone in the following section. The use and effectiveness of preventive measures should be assessed by the dam 

owner in conjunction with a dam safety professional. It may 

not be cost effective to employ these measures for treatment 

of animal intrusions alone; however, coincident benefits 

such as protection against wave erosion and plant intrusion 

may make the measure more fiscally viable.

5.4 Dam Repair Zones

As discussed in this manual, a variety of animals can damage an embankment dam. The damage can be surfical with 

minor impact to dam safety or performance, or the damage 

can directly threaten the integrity of the dam, potentially 

leading to failure. However, all animal impacts should be 

considered undesirable and must be repaired. Dam regulators, owners, and engineers should develop an understanding of the potential impact of an animal intrusion to 

properly evaluate its impact on the safety and performance 

of the dam (refer to chapter 2.0 for a discussion on animal 

intrusion impacts).

Prioritization of necessary repairs is critical to maintain a 

proactive approach to repair and maintenance of a dam. 

With limited available capital, many dam owners may delay 

or avoid necessary dam repairs. In addition, routine safety 

inspections by either regulatory personnel or consulting 

engineers tend to overwhelm dam owners by listing all observed deficiencies without a clear indication of the relative 

importance or seriousness of each deficiency. The relative 

importance and criticality of a specific deficiency depends 

on the size and nature of the observation (length, width, 

depth, area, etc.) as well as its location. 

Developing a well-defined methodology for evaluating 

observed deficiencies will permit dam safety professionals to accurately communicate repair prioritization to dam 

owners. Chapter 3.0 describes an inspection process that 

considers both engineering and biological perspectives for 

a dam divided into five distinct zones. These dam zones cormaterial should consist of soil types (e.g., sand, clay, etc.) 

similar to that of the surrounding embankment. If desired, 

laboratory index testing such as grain size and Atterberg 

Limits of the backfill and embankment materials may be 

performed. To achieve adequate compaction of the backfill 

materials, necessary laboratory testing of backfill materials 

should include a maximum dry density determination by 

either the Standard or Modified Proctor test (ASTM D-698 

or ASTM D-1557). Backfill material should be compacted to 

a minimum of 95% of the maximum dry density and within +/- 2% of the optimum moisture content, as determined 

by ASTM D-698. The completed backfilled surface should 

be smooth and approximately level with the surrounding 

ground surface. Backfill should be placed and compacted in 

lifts of no more than 8 inches thick. A 2 to 4-inch gap can 

be left between the top of the completed backfill surface 

and surrounding ground surface to accommodate topsoil. 
60 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

respond to specific physical areas of the dam as illustrated 

on Figure 5-1 (ASDSO, 2001). The intent of the zones is to 

differentiate and prioritize animal intrusion damages based 

on their potential impact to dam safety or performance. 

Depending on the type of animal intrusion or deficiency 

observed, one or more zones may be considered critical 

and require near term or immediate repair. However, these 

critical zones will vary with the dam as well as the dam 

inspection. Therefore, the zones are not ordered by their 

importance; rather they are simply ordered from upstream 

to downstream. 

The following sections provide a description of each repair 

zone, potential damage from animal intrusion, and suggested preventive measures. These descriptions are limited 

to animal intrusions and their impact to embankment dams. 

However, other deficiencies such as plant intrusion and 

erosion can occur within each repair zone. Where appropriate, restoration and preventive measures should consider all 

observed deficiencies in the area.

Figure 5-1. Remedial dam repair zones.

5.4.1 Dam Repair Zone 1 

Zone 1 begins on the upstream slope at a point approximately 4 vertical feet below the normal pool elevation and 

extends to the center of the crest. A 4-foot vertical distance 

was recommended by Marks, et.al. (ASDSO, 2001) to account for average fluctuations in the normal pool and typical underwater animal burrows. The size of Zone 1 can vary 

significantly from dam to dam because it depends upon the 

distance between the crest elevation and the normal pool 

elevation. This distance is often referred to as freeboard. 

The relative importance of Zone 1 depends upon the crest 

width and freeboard. For a dam with a wide crest and large 

freeboard, animal intrusion within Zone 1 becomes less 

critical. However, as the crest narrows and freeboard lessens, 

the importance of repairing deficiencies in Zone 1 increases 

rapidly. 

The most common animal intrusions within Zone 1 are 

muskrat burrows in which the burrow entrance is underwater as shown on Figure 5-2. However, other intrusions are 

possible depending upon the specific characteristics of the 

crest

zone 1 zone 3

zone 2

zone 4

zone 5

theoretical seepage line

H/2

H/3

4’

Zone 1 Upstream slope area 

Zone 2 Dam crest area

Zone 3 Upper downstream slope area

Zone 4 Lower downstream slope area

Zone 5 Downsteam toe area

Zone 6 Spillway, outlets (not shown)
Chapter 5. Dam Repair and Intrusion Prevention Through Design 61

Figure 5-2. Zone 1 Pentration Problems.

upstream slope

top of

embankment

filter material

(sand or filter fabric)

lowest anticipated pool

concrete 

facing

dam and reservoir that include geographic location of the 

dam, proximate vegetation, and prevailing weather patterns. 

Zone 1 is also susceptible to other forms of deterioration 

including wave erosion, vehicle access, surface water erosion, and plant intrusion.

To effectively repair animal intrusions in Zone 1, the 

reservoir pool must be lowered as far below the observed 

deficiencies as necessary to allow proper access during construction. If the dam owner is unable or unwilling to lower 

the reservoir pool, then the repair costs will likely increase 

dramatically to account for necessary water management 

and diversion.

Preventive measures acceptable for use along the upstream 

slope generally consist of hardened or structural features. 

The intent is to provide a physical barrier to the animal, 

thus making the area much less attractive as a burrow site. 

These features include riprap, concrete facing, revetment 

mats, gabions, large gauge wire mesh, and mechanically 

stabilized earth walls among others. With proper design and 

installation procedures, each of the methods can be successful. Two of the more common measures are riprap and 

concrete facing because they are relatively simple to design 

and provide protection from wave action and plant intrusion as well as animal intrusion. 

A typical cross section of riprap, shown on Figure 5-3 

(Ohio DNR, 1999) should consist of a layer of rock 

riprap overlying bedding material and filter material or 

a geotextile separator. Limits of the protection should 

extend at least 4 feet below the normal pool elevation 

and several feet above depending on estimated wave 

•

Figure 5-3. Riprap Repair in Zone 1.

Figure 5-4. Concrete Facing in Zone 1.

upstream slope

top of

embankment

rock riprap

gravel bedding

filter material

(sand or filter fabric)

lowest anticipated pool

heights and average reservoir fluctuation. Rock size and 

layer thickness will vary significantly from dam to dam 

depending on the reservoir size, prevailing winds and 

other physical characteristics of the area. Therefore, material (e.g. riprap, bedding and filter) sizes and layer thickness, must be based on the anticipated wave action, ice 

thickness, and compatibility with neighboring materials. 

A number of guidelines including Technical Release No. 

69 developed by USDA, Natural Resources Conservation 

Service can assist dam safety professionals in detailed 

design for riprap slope protection.

A typical cross section of concrete facing as shown on 

Figure 5-4 (Ohio DNR, 1999) will resemble riprap in 

that the concrete will overlie a filter material. As with 

riprap, the concrete facing limits should extend at least 

•

crest

zone 1

old burrows theoretical 

seepage line

wave vehicle/animal ruts

erosion

new burows

elevated 

seepage line burrow entrance
62 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

4 feet below the normal pool elevation and several feet 

above, depending on estimated wave heights and average 

reservoir fluctuation. Concrete thickness, compressive 

strength, and reinforcing depend on wave action, freeze/

thaw cycles and other factors.

Regardless of the measure selected, proper implementation 

requires specific design recommendations from a qualified 

dam safety professional.

5.4.2 Dam Repair Zone 2

Repair Zone 2 corresponds to the limits of the dam crest 

and, therefore, overlaps with Zone 1 by one-half of the 

crest width. Overlapping a portion of Zone 1 with Zone 

2 emphasizes the importance and critical nature of both 

zones. This overlap essentially suggests that both zones be 

inspected twice during a dam safety inspection. 

As with Zone 1, the relative importance of Zone 2 depends 

upon the crest width and freeboard. For a dam with a wide 

crest and large freeboard, animal intrusion within Zone 

2 becomes less critical. However, as the crest narrows and 

freeboard lessens, the importance of repairing deficiencies 

increases rapidly. These intrusions may include terrestrial 

animal burrows such those made by groundhog, but most 

typically include ruts and other minor deformations. Zone 2 

is also susceptible to other forms of deterioration including 

vehicle access, surface water erosion, and plant intrusion.

Restoration of animal penetrations within Zone 2 should 

follow the guidelines presented in Chapter 5.3. Any excavation activities within a dam embankment should be coordinated with a dam safety professional. 

Applicable preventive measures for Zone 2 include hardening the crest surface with stone, concrete, or asphalt. These 

measures tend to prevent rutting from animal and vehicular 

traffic. Design of these measures depends upon the specific 

characteristics of the dam and expected loading conditions. 

5.4.3 Dam Repair Zone 3

Repair Zone 3 begins at the crest centerline and extends to a 

point on the downstream slope equivalent to one-third the 

structural height of the dam below the dam crest elevation. 

As with Zone 2, Zone 3 overlaps Zone 2 by one-half of the 

crest width to emphasize the importance of the dam crest 

area. However, the remaining portion of Zone 3 is typically 

considered the least critical dam repair zone relative to dam 

safety issues (ASDSO, 2001). The phreatic surface and zone 

of saturation within the embankment are generally below 

the depths of average animal burrows and should not interfere with restoration activities.

Zone 3 is the most attractive area for burrows of terrestrial 

animal, including groundhog, fox, and coyote. Similar to all 

other zones, Zone 3 is also susceptible to other forms of deterioration including vehicle access, surface water erosion, 

and plant intrusion.

Restoration of animal penetrations within Zone 3 should 

follow the guidelines presented in Chapter 5.3.1 and as 

shown on Figure 5-5. Any excavation activities within a 

dam embankment should be coordinated with a dam safety 

professional.

Applicable preventive measures for Zone 3 (beyond the 

limits of Zone 2) are limited. Use of hardening materials such as stone, riprap, or concrete is generally discouraged by dam safety professionals because they obscure the 

surface and prevent detailed inspection. Installation of wire 

mesh or fencing (e.g., chain link fencing) directly on the 

ground surface can effectively deter to burrowing animals. 

With properly sized openings, the wire mesh deters animal 

intruders and accommodates inspection of the area. However, these materials can represent an obstacle to routine 

maintenance activities such as mowing and be viewed as a 

tripping hazard. 

Figure 5-5. Zone 2 and 3 Repair Procedures.

zone 2

H/3

burrow/den - excavate, 

backfill, compact and seed 

or fill with cementious grout 

and top with dirt and seed

crest

zone 3
Chapter 5. Dam Repair and Intrusion Prevention Through Design 63

5.4.4 Dam Repair Zone 4

Repair Zone 4 extends from the point on the downstream 

slope that is one-third the dams’ structural height below the 

crest to the toe of the downstream slope. Zone 4 is one of 

the two most critical dam repair zones relative to dam safety 

issues because of the proximity of the phreatic surface and 

zone of saturation to the embankment slope. 

Animal and plant intrusions within this repair zone should 

be of major concern to dam owners and dam safety professionals. Any animal intrusion or dam penetration should be 

thoroughly evaluated for potential impact to dam safety and 

for the required repair. 

Restoration of animal burrows within Zone 4 should follow 

procedures presented in Chapter 5.3. However, due to the 

proximity of the phreatic surface to the animal burrow, the 

increased potential of soil migration and, therefore controlling water in the restored burrow must be considered. As 

shown in Figure 5-6, the use of filter materials within the 

backfilled burrow can control internal erosion, and with 

small diameter plastic piping, can manage the flow of water 

in the area. 

livestock paths - fill with soil compact 

 the soil, and 

 revegetate the area

zone 5

zone 4 H/2

2H/3

burrow/den

excavate 

and backfill

install

filter/drain

system

outlet pipe

Figure 5-6. Zone 4 and 5 Repair Procedures.

Similar to Zone 3, use of hardening materials such as stone, 

riprap, or concrete is generally discouraged by dam safety 

professionals because they obscure the surface and prevent 

detailed inspection. The use of wire mesh or fencing as discussed for Zone 3 is also applicable to Zone 4. It is essential 

that restoration and preventive measures in Zone 4 undergo 

review from a dam safety professional prior to implementation. 

5.4.5 Dam Repair Zone 5

Repair Zone 5 begins at the mid-height of the downstream 

slope and extends to a distance of one-half of the dam’s 

structural height horizontally beyond the downstream toe. 

Zone 5 overlaps a large portion of Zone 4 to emphasize the 

most critical portions of both zones and heighten scrutiny 

during inspection. Zone 5 is typically considered the most 

critical zone relative to dam safety issues (ASDSO, 2001) 

because the interception of the phreatic surface and downstream slope is typically located in this zone for homogeneous dams. 
64 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

Animal and plant intrusions in this zone often develop into 

serious conditions involving seepage and piping that are 

progressive and can lead to dam failure if left untreated. The 

installation of filter and drain systems to control soil migration and manage seepage must be considered in Zone 5. 

Similar to Zone 3 and 4, the use of wire mesh of fencing to 

deter animal intruders can also be considered in Zone 5. It 

is essential that restoration and preventive measures in Zone 

5 undergo review from a dam safety professional prior to 

implementation.

5.5 Professional Dam Safety Review

Construction or repair activities on an embankment dam 

should be reviewed by a dam safety professional prior to 

initiation. Due to the complexity of interaction among 

animal penetrations, the phreatic surface, slope stability, and 

other deficiencies, the impact of excavation activities on a 

dam can be unpredictable without thorough review by a 

qualified professional. This review should include the following elements at a minimum:

Evaluation of the existing dam relative to the position of 

the phreatic surface and slope stability through review of 

pre-existing inspection reports, design drawings, design 

memoranda, and owner observations.

Assessment of the impact of excavation given the phreatic 

surface position and physical characteristics of embankment materials (material type, density, plasticity, etc.). 

Evaluation of the restoration and preventive scheme 

proposed.

5.6 Sequenced Repair Program

Currently, dam safety inspections provide a comprehensive 

list of deficiencies observed at the time of the inspection. 

The list is generally separated into physical areas of the dam 

including the upstream slope, crest, downstream slope, 

emergency spillway, and principal spillway. However, in 

most cases, the list is not prioritized for the dam owner. 

Consequently, the dam owner is left with a long list of deficiencies with little guidance on immediate, near-term, and 

long-term repair items. 

Considering that most dam owners do not have the financial 

means to address all deficiencies quickly, a prioritization 

methodology should be established for dam repair. The following sequence is one that provides the owner, regulator, 

•

•

•

and dam safety engineer with a reasonable opportunity to 

effectively evaluate the condition of an earthen dam (ASDSO, 2001). It must be noted that the following sequence 

is intended for general guidance only. Specific dam inspections may substantially deviate from the following sequence 

based on the needs and requirements of the individual dam. 

Year 1. (from date of last inspection) Repair animal 

penetrations that exhibit seepage, soil migration, or have 

caused slope instability in Zones 1, 4, or 5. Preventive 

measures should be installed where appropriate.

Year 2. Repair penetrations in Zones 2 and 3. If deemed 

necessary, initiate investigation, analysis, and preliminary 

design of major repair activities. 

Year 3. Complete design and begin construction of major 

repair activities.

Year 4. Complete construction of major repair activities 

and establish an operation and maintenance program 

that will manage animal intrusions and penetrations on a 

frequent and regular basis. 

If dam failure is judged imminent or if dam safety or operation has greatly diminished, the above sequence may not be 

applicable. In these cases, a dam safety professional must be 

advised of the situation to develop a revised schedule.

5.7 Mitigation Through Design 

5.7.1 Muskrat 

Some of these design criteria are referred to as “overbuilding” however, they are generally effective at preventing 

serious muskrat burrow damages. The design measures 

are adapted from the following references: University of 

Nebraska, 1994; University of Missouri Extension, 1999; 

ASDSO, 2001; Connecticut DEP, 1999; USDA, 1991; and 

South Carolina DNR, 2003. 

Construct the upstream slope of the dam to a 3H to 1V 

slope. Muskrats favor steep slopes so gentle slopes will be 

less attractive (Figure 5-7). 

Construct the downstream slope of the dam at a 2H to 

1V slope with a crest width of not less than 8 feet, preferably 10 to 12 feet. 

•

•

•

•

•

•
Chapter 5. Dam Repair and Intrusion Prevention Through Design 65

gentle slope 

discourages burrowing

steep bank encourages burrowing

any slope steeper than 3’ to 1’ 

should be avoided

sod cover

1’

2’

1’

3’

20’ minimum

23’ perferred

less than 3’

less than 20’

new den

normal water level

(does not rise more than 6”)

more than 6”

3’

Proper Embankment Construction

Improper Embankment Construction

The normal water level in the pond should be at least 3 

feet below the top of the dam and the spillway should 

be wide enough that relatively frequent storms (less than 

the 10 year storm event) will not increase the level of the 

water for any length of time. 

Design for a minimum width of 20 feet at normal water 

level.

Bind soil adequately by sodding well.

Protect the crest from muskrat by applying compacted 

dense-graded aggregate base course 4 to 6 inches thick.

Construct a 10-foot-wide shelf projecting from the face 

of the dam into the reservoir at the water line. This shelf 

will act as a muskrat barrier and also reduce wave action 

erosion.

Place stone rip-rap underlain by fine filter stone and 

geotextile (high strength, non-woven) extending from 3 

to 4 feet below the water line to 1 foot above the water 

line. Riprap size and thickness will depend upon specific 

•

•

•

•

•

•

Figure 5-7. Proper dam construction can reduce muskrat damage.

reservoir characteristics. The riprap will prevent muskrat 

from burrowing into the dam.

Use an appropriate gabion wall system and/or enlarged 

reinforced concrete outlet works structures to act as exclusion systems at the toe of the downstream slope.

Embed 1 to 2-inch welded wire or chain link fencing 

into the dam upstream face. Mesh wire should extend 

from 3 to 4 feet below the water line to 1 foot above the 

water line. Lay the wire flat against the banks and fasten 

it down every few feet to secure the wire. It is likely that 

portions of the mesh below the water surface will corrode over time and require replacement. 

Using a narrow trenching machine, cut a vertical trench 

extending the full length of the embankment in the 

centerline of the earth fill. The trench should extend from 

3 to 4 feet below the water line to 1 foot above the water 

line. Fill the trench with concrete to create a core that 

will prevent muskrat from digging through the embankment.

•

•

•

flooded den

high water level

normal water level
66 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

Design water control structures with a concrete apron to 

prevent muskrat burrows from damaging these facilities.

Several of the above design components indicate placement 

of the barrier 3 to 4 feet below the water line of the normal 

pool. It should be noted that if the barriers are not placed 

at least 3 feet (and preferably 4 feet) below the water line, 

then the muskrat will burrow underneath the barrier and 

penetrate the embankment; failure of the slope protection 

system and embankment damages will result.

5.7.2 Beaver 

Structures or techniques to prevent beaver damage can often 

be included in initial engineering plans or added during 

dam upgrades and repairs. The following techniques have 

been adapted from the following references: University of 

Nebraska, 1994; North Carolina State University, 1994; Wilson, 2001; New York State DEC, 2002; Porter, 2003; Barnes, 

1991; Virginia Cooperative Extension, 2000; and FEMA, 

2000.

Gently slope the embankment (3H to 1V or flatter) to 

discourage burrowing and minimize the probability of 

beaver dam construction.

Install spillway risers so that they open upstream instead 

of toward the dam.

Place riser structures far from the face of the dam in the 

deepest water possible.

•

•

•

•

Protect large risers from clogging by installing mesh 

bars (at least 5 inches square) or hog pen panel (4 x 4 

inches). This will prevent beaver from entering the trash 

rack.

Protect intakes with a deep water cage or fence to prevent 

plugging. 

Replace the standard manhole cover on top of the riser 

tower with a “beehive” grate. This cast iron dome allows 

drainage during high water events, even if the lower 

orifices are blocked. 

Install a single strand, high-tensile electric wire across 

active beaver paths or around the shoreline just above the 

slope where beavers would exit the water. The electric 

wire should be staked about 3 to 4 inches above the soil 

surface and can be powered by a direct 110-volt charger 

or a rechargeable battery pack. After repeated shocks, the 

beaver will usually relocate to another area. Public safety 

issues and concerns must be addressed when considering 

this option.

Install fencing around outlets to prevent plugging. Secure 

the fence to the reservoir bottom with metal posts. Fencing should be about 5 feet high, made of heavy-gauge 

woven wire with no larger than 6-inch openings. It 

should extend 10 to 20 feet out from the outlet. Before 

installing the fence, debris should be removed from the 

outlet (Figure 5-8). 

•

•

•

•

•

Figure 5-8. Install fencing around culverts and outlets 

to prevent beavers from blocking flow.

The South Carolina Dam 

Safety Office indicates 

that using siphons and 

other “non-trickle” 

principal spillway systems 

may be effective against 

beaver, but their success 

is not documented. 
Chapter 5. Dam Repair and Intrusion Prevention Through Design 67

Avoid These Water Level Control Devices at Dams

Because these devices require partial obstruction of spillways or outlet pipes, their use at a dam 

should be strictly prohibited. Obstruction of spillways or outlets can cause reservoir levels to rise 

resulting in overtopping of the dam, erosion of earthen spillways and other detrimental impacts.

lashing (wire or rope)

Elbow and standpipe are 

optional. Needed only to manage 

water-level if maintaining 

pond is an objective

beaver dam

8” diameter

40 PVC pipe

1” re-bar

6” long

intake device

pond side

T-joint tilted with a drain 

plug may replace elbow

Figure 5-9. The Clemson Beaver Pond Leveler is a passive but effective means to control water levels through a beaver dam.

green sticks separate 

logs to allow water flow

15-20 cm green logs

roofing tin

Figure 5-10. A 3-log drain manipulates 

water levels through a beaver dam.

beaver dam

flow

beaver dam

Figure 5-11. PVC Beaver Drain Pipe

Figure 5-12. Massachusetts Beaver Pond Leveler

20’
68 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

Install a layer of riprap on the upstream side of the 

embankment to prevent burrowing. The riprap should 

extend from 4 feet below to 2 feet above normal water 

levels. 

5.7.3 Mountain Beaver

It may be possible to exclude mountain beavers from a dam 

by installing a rabbit-proof fence (chain-link, chicken wire, 

etc.) around the embankment. The bottom of the fence 

must be tight against the ground or, for better protection, 

buried about 1 to 2 feet (Pehling, 2003).

5.7.4 Groundhog 

It is possible to discourage groundhogs from burrowing 

in an earthen dam by armoring the structure with rock or 

other hard materials (Michigan State University Extension, 

1998). 

It is also possible to exclude groundhogs from an earthen 

dam by installing a fence around the area of concern. 

Groundhogs are good climbers so the fence should be at 

least 3 feet high and made of heavy poultry wire or 2-inch 

mesh woven wire. To prevent burrowing underneath the 

fence, it should be buried 10 to 12 inches into the ground 

or bent into an L-shaped angle (pointing away from the 

excluded area) buried 1 to 2 inches into the ground. For 

added protection, an electric wire placed 4 to 5 inches off 

the ground and 4 to 5 inches away from the fence may be 

installed (University of Nebraska, 1994). Public safety issues 

and concerns must be addressed when considering this option.

5.7.5 Pocket Gopher 

Fencing is of limited use for protecting earthen dams from 

pocket gophers; the method is expensive and generally not 

practical because pocket gophers burrow so deeply underground. However, if fencing is used to exclude pocket gophers from the dam, it should be buried at least 20 inches 

into the ground and extend 6 to 8 inches above the ground 

(USDA, 1991).

5.7.6 North American Badger

Fencing may be used to exclude badgers from an earthen 

dam. The fence should be made of mesh wire and it should 

be buried to a depth of 12 to 18 inches to prevent badgers 

from burrowing underneath. This control method may not 

• be practical for protecting large areas because installation 

can be costly and time consuming (University of Nebraska, 

1994).

5.7.7 Nutria

There are several design measures that can be implemented 

to reduce nutria damage. 

Install fencing around the dam embankment. Fences 

should be about 4 feet high with at least 6 inches of 

fencing buried underground.

Armor the embankment with riprap to discourage burrowing.

Contour embankment slopes to an angle less than 45o to 

discourage burrowing. 

5.7.8 Prairie Dog 

The use of fencing to exclude prairie dogs from a dam is 

a potential management tool, although it is rarely practical because prairie dogs burrow so deeply underground. If 

fencing is chosen as a control method, a tight-mesh, heavygauge, galvanized wire fence should be used, with 2 feet 

buried in the ground and 3 feet remaining above ground 

(University of Nebraska, 1994).

Visual barriers may also discourage prairie dogs from inhabiting an area. Prairie dogs prefer areas of low vegetation 

to provide a clear view of their surroundings and to improve their ability to detect predators. Objects such as fences 

or hay bales that are strategically placed to block prairie dog 

views may reduce suitability of the habitat. High construction and maintenance costs generally reduce the viability of 

this option (University of Nebraska, 1994).

5.7.9 Ground Squirrel

Fencing is not usually a practical method of control for 

ground squirrels because they are able to climb over or burrow under most exclusion structures. Routine weed control 

and vegetative management may limit some damage, but 

the effectiveness of this method is usually limited as well 

(USDA, 1991).

•

•

•
Chapter 5. Dam Repair and Intrusion Prevention Through Design 69

1/4” x 4 1/2” carriage bolt

galvanized woven wire

3” treated pole

7’ long

72”

galvanized

fencing

60”

56”

23” apron

(old fencing)

28”

5.7.10 Armadillo 

It is possible to exclude armadillos from an earthen dam by 

installing a fence or barrier around areas of concern. Armadillos can both climb and burrow so the fence should be 

slanted outward at a 40o angle with a portion buried underground sufficient to maintain the fence’s pitch. 

5.7.11 Livestock

Fencing is a highly effective method of protecting earthen 

dams from domestic livestock and is moderately effective 

with free-ranging or wild grazing animals (USDA, 1991). 

Heavy wire fences, wooden post fences, or electric fences 

may be used (University of Nebraska, 1994).

5.7.12 Crayfish

No design techniques are effective at discouraging crayfish 

inhabitation.

5.7.13 Coyote

Fencing can be used to 

exclude coyotes from a 

dam. Both wire and electric fences will work, and 

a combination of the two 

will probably be most effective. Net wire fences 

should be about 5 feet high 

with barbed wire at ground 

level or a buried wire 

apron. Horizontal spacing of the mesh should be less than 6 inches and vertical 

spacing should be less than 4 inches. Electric fences usually 

consist of strands of smooth, high-tensile wire stretched to 

a tension of 200 to 300 pounds. Studies have shown that 13 

strands of charged wire effectively protected pastures from 

coyote predation (University of Nebraska, 1994). 

5.7.14 Mole and Vole

Fencing may be useful for mole control in small dams. The 

fence should be made of rolled sheet metal or hardware 

cloth, with at least 12 inches buried underground and 12 

inches extending aboveground. It is also possible to discourage moles from burrowing in an earthen dam by packing the soil with a roller to reduce soil moisture. This will 

reduce the habitat’s attractiveness to moles (University of 

Nebraska, 1994).

Fencing of large-scale areas is generally not a cost-effective 

method of vole control (University of Nebraska, 1994). 

5.7.15 River Otter

Fencing may be used to exclude river otters from an earthen 

dam. The fence should be constructed of mesh wire (3 x 3-

inch or smaller) or hog-wire. Dam owners should regularly 

check the fence to ensure that it has not been spread apart 

Studies have shown that 

13 strands of charged wire 

effectively protected pastures 

from coyote predation.

Figure 5-13. Installation of a net fence with wire overhang 

and buried apron is an effective coyote exclusion method.
70 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

or raised to allow otters to enter (University of Nebraska, 

1994). 

5.7.16 Gopher Tortoise 

Fencing the dam embankment may be practical for protecting small areas from gopher tortoise damage (University of 

Nebraska, 1994). 

5.7.17 Red and Gray Fox

Fencing can be used to exclude foxes from an area of concern. Both wire and electric fences will work, and a combination of the two will probably be most effective. Net wire 

fences should be constructed so that all openings are less 

than 3 inches. The bottom should be buried 1 to 2 feet into 

the ground with at least 1 foot above ground. For an effective electric fence, there should be at least three charged 

wires spaced 6 inches, 12 inches, and 18 inches above the 

ground (University of Nebraska, 1994).

5.7.18 Canada Goose

It is often possible to discourage Canada goose inhabitation 

by installing fencing, rock barriers, or vegetative barriers 

around shorelines. Fencing can be constructed out of a variety of materials including mylar tape, metal mesh, plastic or 

synthetic mesh, electric wires, or wood. Fences should be at 

least 25 inches tall and should not contain openings greater 

than 3 inches (Virginia Cooperative Extension, 2001b).

5.7.19 American Alligator 

Fencing may be used to exclude alligators from earthen 

dams. The fence should be at least 5 feet high with the top 

edge angled outward (University of Nebraska, 1994).

5.7.20 Ants

There are no exclusion methods or design measures effective against ant inhabitation

5.8 Monitoring 

Once a dam specialist identifies the burrow and the species 

creating or occupying it, the burrow(s) would be filled and 

a prevention technique implemented as appropriate. The 

next step to maintaining safe dam operation is to monitor 

the effectiveness of the remedial action (e.g., has the riprap effectively deterred muskrat activity?). In many cases, 

regular dam inspections and swift burrow mitigation (and 

preventive actions when needed) will adequately preserve 

safe dam operations. However, it is possible for a dam to 

become overrun by nuisance animals, or for several species 

to cumulatively compromise safe dam operations. In these 

cases, repair actions are only partial solutions. Monitoring can help the dam owner determine whether additional 

mitigation is necessary. 

In general, it is recommended that the dam owner inspect 

the dam once every 3 months after first finding and repairing animal damage. The frequency is aimed at confirming 

the animal has not returned to the dam once the burrow is 

removed. Once burrows are identified, the owner should 

consider implementing a preventive action if a burrow 

occurred in one of the critical dam zones (see Chapter 5.4 

for a discussion on animal burrows in critical dam zones). 

Understanding the potential fiscal limitations of dam owners, the most realistic approach is to use the fewest actions 

needed to ensure dam safety. As a guideline, if the dam 

owner finds new animal burrows in the dam on two consecutive inspections following repair and preventive actions, 

then implementing a wildlife control strategy is probably 

necessary to maintain safe dam operations (see Chapter 6.0 

for a discussion on wildlife control).
Chapter 6. Mitigating Damaging Wildlife 71

6.0 Mitigating Damaging Wildlife 

This chapter of the manual details methods for managing 

wildlife populations. General wildlife management information is provided first, followed by specific management 

information for the 23 species considered in this manual. 

The application of this data in the dam environment can be 

beneficial and at times necessary to protect human populations from the disastrous effects of dam failure. However, 

applied indiscriminately, these methods can adversely affect the dam environment, protected wildlife species, and 

even human populations. For this reason, nuisance wildlife 

management practices should be implemented only with 

coordination and input from state and federal wildlife 

agencies and the county agent responsible for toxicant and 

fumigant registration and application (Appendix A contains 

state wildlife contacts). 

6.1 Compliance with State and Federal Regulations

6.1.1 Conformity to Federal Regulations

As the vast majority of surveyed states indicate, the dam 

owner is responsible for the identification and mitigation 

of nuisance wildlife at dams. Although the dam owner is 

empowered by the state dam safety official to manage a 

dam toward safe operation, the dam owner must abide by 

applicable federal and state regulations when implementing 

nuisance wildlife management measures. The Endangered 

Species Act of 1973 (ESA), the Migratory Bird Treaty Act 

of 1918 (MBTA), and the Federal Insecticide, Fungicide, 

and Rodenticide Act of 1996 (FIFRA) are three federal laws 

that must be complied with during application of wildlife 

management methods. The ESA protects species of plants 

and animals that are in danger of extinction. Under the ESA, 

it is illegal for anyone to “take” a species listed as threatened 

or endangered. 

The ESA defines “take” as, “to harass, harm, pursue, hunt, 

shoot, wound, kill, trap, capture, or collect or attempt to engage in any such conduct” (USFWS, 2002a). The MBTA was 

established to conserve migratory bird species in the United 

States and prohibits the hunting, trapping, possession, and 

transfer of listed species except under the terms of a valid 

permit or during authorized hunting seasons (USFWS, 

2002b). 

Species that are discussed in this manual and protected under the ESA and the MBTA include: 
72 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

Gopher Tortoise (Gopherus polyphemus). This species is listed 

as Threatened under the ESA throughout its range of 

Mississippi, Louisiana, and portions of Alabama, and is 

protected by state laws in Alabama, Georgia, Florida, and 

South Carolina.

The American Alligator (Alligator mississippiensis). This 

species is listed as “Threatened by Similarity of Appearance to a Threatened Taxon” under the ESA throughout 

its range of Alabama, Arkansas, Florida, Georgia, Louisiana, Mississippi, North Carolina, Oklahoma, South 

Carolina, and Texas. This designation means that the 

American Alligator is protected under the ESA because 

of its similarity in appearance to the American Crocodile 

(Crocodylus acutus). The American Crocodile is classified as 

Endangered under the ESA. The USFWS determined that 

in order to adequately protect the American Crocodile, 

which is often mistaken for the American Alligator, the 

USFWS must also protect the American Alligator. Therefore, though populations of the American Alligator are 

healthy throughout its range, it is afforded full protection 

under the ESA.

Point Arena Mountain Beaver (Aplodontia rufa nigra). This 

subspecies is listed as Endangered throughout its range of 

California. 

Utah Prairie Dog (Cynomys parvidens). This species is listed 

as Threatened throughout its range of Utah. 

Northern Idaho Ground Squirrel (Spermophilus brunneus brunneus). This subspecies is listed as Threatened throughout 

its range of Idaho. 

Canada Goose (Branta canadensis). This species is protected 

under the MBTA throughout its range of the United 

States.

If dam owners suspect that one of these species is damaging the earthen dam, then the dam owner must contact the 

USFWS and the state wildlife agency to discuss management 

options. While it is often possible to relocate these animals 

with permits and guidance from the USFWS and the state 

wildlife agency, the permitting agency must be consulted 

prior to taking any action. It should be noted that the list of 

protected species can and does change, and regular contact 

with an agency is required to ensure that no protected species are adversely affected. 

•

•

•

•

•

•

While difficult to predict each potential circumstance, there 

may be cases when management of a species not protected 

by the ESA or MBTA may result in the illegal taking of a 

protected species that is associated with the targeted nuisance species. For example, the endangered black-footed 

ferret (Mustela nigripes) depends on the burrows of prairie 

dog colonies for survival. Mitigation against the prairie dog 

may impact the ferret. Similarly, the eastern indigo snake 

(Drymarchon corais couperi) is afforded refuge by gopher tortoise burrows; thus, managing a dam for the tortoise could 

have secondary effects on the indigo snake. As some species show interdependencies on others, it is recommended 

that coordination with state and federal wildlife agencies be 

conducted before management of any species, protected or 

not, occurs. 

Last, FIFRA divides pesticides, including toxicants and 

fumigants, into two categories: General Use Pesticides and 

Restricted Use Pesticides. General Use Pesticides will not 

ordinarily cause unreasonable adverse effects on the user or 

the environment when used as directed and as such, they 

are commercially available to the public. Restricted Use 

Pesticides, however, could cause adverse effects to the user 

or the environment even when used correctly. Restricted 

Use Pesticides can only be purchased by a certified pesticide applicator and applied by or under the supervision of 

a certified pesticide applicator, in accordance with FIFRA. 

Appropriate disposal of pesticide containers is also required.

6.1.2 Conformity to State Regulations

Certain wildlife species are protected by the state even 

though they are not listed as Federally threatened or endangered; each state determines its own regulations with 

regard to protected species. Furthermore, hunting and 

trapping regulations in regard to furbearer, game, and nongame species vary from state to state. For these reasons, it 

is recommended that a dam owner contact the appropriate 

state wildlife agency for information about mitigation of 

wildlife species, and hunting and trapping seasons, licenses, 

and permits before attempting to remove an animal from 

the dam environment or before any wildlife management 

actions are taken. As with federal laws, the list of protected 

species can change from year to year and regular contact 

with an agency is required to ensure that no protected species are adversely affected. 

Finally, legal use of specific toxicants and fumigants varies from state to state; one state may allow a toxicant that is 

banned in another. As such, it is recommended that coor-
Chapter 6. Mitigating Damaging Wildlife 73

dination with the state wildlife agency or county agent be 

conducted to determine which substances are allowed for 

use in each state. If toxicants or fumigants are selected as the 

management option, it is recommended that:

The substance is used according to direction and precaution;

The substance is stored securely in original containers 

away from children, animals, food, and feed;

The substance is applied so as not to endanger humans, 

livestock, crops, beneficial wildlife, or water supply, or 

leave illegal residues; 

Excess substance is not dumped, and associated equipment is not cleaned near ponds, streams, or wells; and 

Substance containers are disposed of properly at an appropriate landfill facility.

6.2 Muskrat Management Methods 

6.2.1 Muskrat Control Through Habitat Modification 

(South Carolina DNR, 2003; University 

of Nebraska, 1994; Michigan State 

University Extension, 1998; USDA, 1991)

Mow regularly to remove food supply. Specifically, remove 

cattails, arrowhead, and other plants that grow on the fringe 

of the reservoir. 

Implement an aquatic vegetation control program to 

reduce aquatic vegetation preferred by the muskrat for food 

and cover. Muskrat populations can be effectively managed 

by eliminating food sources. The vegetation control program can be achieved through several management approaches: 

Herbicides are widely used to control aquatic vegetation. Out of the 200 herbicides registered with the U.S. 

Environmental Protection Agency, only 8 are available 

for aquatic uses, and only 6 of those 8 are widely used 

(2 herbicides are limited to use in 17 western States’ 

irrigation systems under Bureau of Reclamation control). Coordination with the state agency responsible for 

aquatic plant management is required to ensure that the 

appropriate herbicide is selected based on management 

goals and that herbicides are lawfully applied.

•

•

•

•

•

•

Hand Removal of preferred muskrat vegetation can be 

implemented; however this method is labor-intensive 

and needs to be repeated frequently to keep vegetation, 

especially perennial plants, under adequate control. Hand 

removal can be combined with herbicide application.

Mechanical Removal utilizes small and large weed harvesters 

to remove vegetation around the shoreline. This method 

achieves immediate vegetation control in small dams 

and does not carry water-use restrictions after treatment, 

unlike herbicide application. However, weed harvesters cannot be used in all environments—for example, 

obstructions may preclude harvester use. This method 

is usually higher in cost, slower, and less efficient than 

other available methods.

Manipulate water levels in the reservoir to create an 

undesirable habitat for the muskrat. A 2-foot drawdown in 

the reservoir during the winter months can be an effective 

muskrat management tool. Drawdown allows a dam specialist to identify and repair muskrat holes in the upstream 

slope (refer to Chapter 5.3.1 for burrow repair discussion), 

and may drive away resident muskrats, which need adequate 

water levels. It is recommended that muskrats be trapped 

and removed during the drawdown; however, trapping and 

relocation should be coordinated with the appropriate state 

agency, since a permit may be required. 

A secondary benefit of water level manipulation is the potential drying and freezing of aquatic plants—the muskrat’s 

primary food supply—as the plants are exposed to air. It 

should be noted that some aquatic plants are tolerant of 

drawdown and may actually increase after a drawdown; 

therefore, drawdown as a primary aquatic plant management method is not recommended.

6.2.2 Muskrat Control Through Trapping 

(University of Nebraska, 1994; 

South Carolina DNR, 2003)

The most effective types of traps for muskrat include the 

Conibear® traps No. 110 and 120, and leghold traps like the 

long spring No. 1, 11⁄2 or 2, and similar coil spring traps 

(Figure 6-1 and 6-2). The Conibear® traps are preferred 

because they are effective in shallow and deep water settings, easy to set up, and kill the muskrat quickly, preventing 

escapes. The Conibear® and leghold traps are most effective 

when set close to the den entrance in the “runs” or trails 

carved into the reservoir bottom by the muskrat’s hind feet. 

Runs can be easily seen in clear water, or can be felt with 

•

•
74 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

Figure 6-1. To capture muskrats, leghold traps should be set along runways, den openings, 

or natural resting areas. Conibear No. 110 traps should be set in the water.

Leghold Trap

Conibear® - Type Body 

Gripping Traps

Figure 6-2. Muskrat traps can be effectively set in four locations. Bait traps with carrots, potatoes, sweet potatoes, or apples.

trail set

rock set

den set

feed bed set

trap set in trail 

through rushes

Field testing in a 100-acre 

rice field (36 Conibear®

110 traps were set) and a 

60-acre minnow pond (24 

11⁄2 leghold traps were set) 

yielded an effective muskrat 

removal rate of 93.3% and 

87.5% for the Conibear®

and leghold traps, 

respectively. All tripped 

traps were 100% effective. 
Chapter 6. Mitigating Damaging Wildlife 75

the hands or feet in murky or deep water. Poles can be used 

to anchor the trap in front of the den (Figure 6-3). 

Where legal, homemade stovepipe traps can also be effective. This type of trap is cheap, simple, and easy to make, but 

it requires more time and effort to set. A trap can be constructed by forming sheet metal into a 6 x 6-inch rectangular box, 30 to 36 inches long with heavy-gauge hardware 

cloth or welded wire doors. The doors should be hinged at 

the top to allow entry from either end, but no escape out of 

the box. The trap should be set right up against the primary 

den entrance to be most effective.

6.2.3 Muskrat Control Through Fumigants 

(University of Nebraska, 1994)

No fumigants are registered for muskrat control.

6.2.4 Muskrat Control Through Toxicants 

(University of Nebraska, 1994)

Zinc phosphide (63% concentration) is the only toxicant 

Federally registered for muskrat control. To make a bait, 

vegetable oil is applied to cubes of apples, sweet potatoes, 

or carrots; the zinc phosphide is sprinkled on top; and the 

ingredients are mixed together thoroughly. The bait is then 

placed at the burrow entrance, on floating platforms (Figure 

6-4), or on feeding houses. Zinc phosphide is a Restricted 

Use Pesticide and may therefore, only be purchased and 

applied by a certified pesticide applicator. Zinc phosphide 

should always be used as directed. Dam owners should contact the appropriate state wildlife agency regarding legality 

of toxicant use in their state. 

Anticoagulants such as pivalyl, warfarin, diphacinone, and 

chlorophacinone have also been registered for muskrat 

control in some states. These anticoagulants come in the 

form of a “lollipop” made of grain, pesticide, and melted 

paraffin. As with zinc phosphide, anticoagulant baits can 

Figure 6-3. Pole set at muskrat den.

water line

bamboo pole

muskrat den 

entrance
76 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

be placed at burrow entrances, on floating platforms, or on 

feeding houses. Dam owners should contact their state wildlife agency to see which, if any, anticoagulants are registered 

in their state. 

6.2.5 Muskrat Control Though Frightening 

(University of Nebraska, 1994)

Frightening is not an effective method of muskrat control.

6.2.6 Muskrat Control Through Repellents 

(University of Nebraska, 1994)

No repellents are registered for muskrat control.

6.2.7 Muskrat Control Through Shooting 

(University of Nebraska, 1994)

Shooting can be an effective method of eliminating a few 

individual muskrats. Hunting efforts are most successful 

at dawn and dusk. Dam owners should contact their state 

wildlife agency for information on hunting regulations and 

restrictions. 

6.3 Beaver Management Methods

6.3.1 Beaver Control Through Habitat 

Modification (University of Nebraska, 1994; 

University of New Hampshire Cooperative 

Extension, 1997; USDA, 1994)

Clearing trees and shrubs near the reservoir will reduce potential food sources and habitat and may discourage beaver 

inhabitation of a dam. Daily destruction of existing dams 

Researchers in Louisiana 

found that deep water 

beaver dams could be 

removed more effectively 

than shallow water 

beaver dams, and that 

it was more effective to 

remove beaver dams in 

later summer rather than 

early or midsummer. 

and removal of dam construction material will sometimes 

cause existing beaver colonies or individuals to relocate. 

6.3.2 Beaver Control Through Trapping 

(University of Nebraska, 1994)

In most situations, trapping is the most effective and economical method of controlling beaver damage. Various types 

of traps can be used, but the Conibear® No. 330 is generally considered the most effective (refer to Figure 6-1 for trap 

types). It is designed primarily for water use, and works 

equally well in deep and shallow areas. Conibear®-type 

traps should be set on dry, solid ground to prevent injury 

to the person setting the trap. Once the trap is set, it can be 

Figure 6-4. Toxicant bait platforms.

pulley system

concrete block

tie-down
Chapter 6. Mitigating Damaging Wildlife 77

moved to the water and anchored down with stakes. Traps 

can be effectively set in front of lodge entrances, in front of 

a hole in the beaver dam, or on underwater beaver trails. 

Leghold traps (No. 3 double spring or larger) are also commonly used to capture beavers. This type of trap should be 

used with a drowning set attachment so that the captured 

beaver cannot escape. Proper placement is very important 

with leghold traps. They should be set just at the water’s 

edge, slightly underwater, with the pan, jaws, and springs 

covered lightly with leaves or debris. There must be a cavity 

under the pan for the trap to properly trigger. Leghold traps 

are most effective when they are set slightly off-center on 

an underwater beaver trail. 

Snares can also be used to capture beavers. The equipment 

costs less than trapping equipment, and snares can be set 

so that the beaver is caught alive and can then be relocated. 

Snares are frequently set under logs, near bank dens, and 

next to castor mounds. 

Dam owners should contact their state wildlife agency 

regarding trapping regulations and seasons and regulations 

regarding live trapping and relocation. 

6.3.3 Beaver Control Through Fumigants 

(University of Nebraska, 1994)

No fumigants are registered for beaver control.

6.3.4 Beaver Control Through Toxicants 

(University of Nebraska, 1994)

No toxicants are registered for beaver control. 

6.3.5 Beaver Control Through Frightening 

(University of Nebraska, 1994)

Frightening is not an effective method of beaver control.

6.3.6 Beaver Control Through Repellents 

(University of Nebraska, 1994)

No repellents are Federally registered for beaver control. 

6.3.7 Beaver Control Through Shooting

Shooting may also be used to remove small populations of 

beavers. If permitted by law, night shooting is most effective; however, hunting in the early evening and early morning hours can also be effective. Dam owners should contact 

their state wildlife agency for information on hunting 

regulations and restrictions. 

6.4 Mountain Beaver Management Methods

The Point Arena mountain beaver is a Federally listed endangered subspecies and therefore subject to the provisions of 

the Endangered Species Act. This subspecies is found only in 

California. Dam owners in California who suspect that they 

have a mountain beaver problem should contact the USFWS 

and the California Department of Fish and Game for definitive species identification and management guidance.

6.4.1 Mountain Beaver Control Through Habitat 

Modification (University of Nebraska, 1994)

Removal of plants such as sword fern, bracken fern, or salal 

may reduce the attractiveness of a site to mountain beavers. 

6.4.2 Mountain Beaver Control Through Trapping 

(University of Nebraska, 1994)

Trapping is an effective method of controlling mountain 

beavers. The Conibear® No. 110 is most commonly used 

(refer to Figure 6-1). The trap should be set in the main 

burrow entrance, anchored with three stakes. Trapping is 

most effective in warm months when mountain beaver are 

most active. 

Live trapping is also possible using double-door wire mesh 

traps such as the Tomahawk. This method of trapping is 

recommended in areas where pets or livestock could accidentally be captured. The trap should be placed in the main 

burrow entrance with vegetation arranged along the inside 

and outside of the trap. The trap should be wrapped with 

black plastic and covered with soil to protect the captured 

mountain beavers from the weather. Captured animals 

should be placed in a dry burlap sack and euthanized or 

relocated to an appropriate location. 

Dam owners should contact their state wildlife agency regarding trapping regulations and seasons and requirements 

for euthanasia or relocation. 

6.4.3 Mountain Beaver Control Through Fumigants 

(University of Nebraska, 1994)

No fumigants are registered for mountain beaver control.
78 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

6.4.4 Mountain Beaver Control Through Toxicants 

(University of Nebraska, 1994)

No toxicants are Federally registered for mountain beaver 

control. Some toxicants may be registered in certain states, 

though, so dam owners should contact their state wildlife 

agency regarding this option.

6.4.5 Mountain Beaver Control Through Frightening 

(University of Nebraska, 1994)

Frightening is not an effective method of controlling mountain beaver.

6.4.6 Mountain Beaver Control Through Repellents 

(University of Nebraska, 1994)

Repellents are effective for controlling mountain beaver that 

are causing damage to trees/seedlings, but this method is 

not practical for preventing damage to earthen dams.

6.4.7 Mountain Beaver Control Through Shooting 

(University of Nebraska, 1994)

Mountain beavers are nocturnal animals that spend most of 

their time below ground; therefore, shooting is not a practical method of mountain beaver control.

6.5 Groundhog Management Methods

6.5.1 Groundhog Control Through Habitat 

Modification (Michigan State 

University Extension, 1998)

It is possible to discourage groundhog inhabitation by 

mowing vegetated areas of the earthen dam to remove 

cover.

6.5.2 Groundhog Control Through Trapping (USDA, 

1991; University of Nebraska, 1994)

Trapping is an effective method of controlling limited 

populations of groundhogs. Steel leghold traps (No. 2) 

(refer to Figure 6-1) and live traps are both commonly 

used. Traps should be set at the main burrow entrance or on 

major travel lanes. Live traps, which can be purchased commercially or home-built, require bait such as apple slices, 

carrots, or lettuce. Groundhogs captured in live traps should 

be euthanized or relocated to a suitable habitat where they 

will not cause further damage. 

Conibear® traps (110, 160, or 220) may also be used in 

certain situations (refer to Figure 6-1). They should not be 

used where they could capture domestic animals or livestock. Conibear® traps should be set in major travelways or 

at the main entrance of a burrow system. No bait is necessary. 

Dam owners should consult with their state wildlife agency 

regarding specific trapping regulations and requirements for 

euthanasia or relocation.

6.5.3 Groundhog Control Through Fumigants 

(University of Nebraska, 1994)

Use of the commercial gas cartridge is the most common 

method of groundhog control. The cartridge is ignited and 

placed in the burrow with all other entrances sealed. As the 

cartridge burns, it produces carbon monoxide and other 

gases lethal to the groundhog. Gas cartridges are General 

Use Pesticides that can usually be purchased at local farm 

supply stores or pesticide dealers. They should be used with 

caution and in accordance with the directions on the label. 

Aluminum phosphide is a Restricted Use Pesticide that 

may be applied by a certified pesticide applicator to control 

groundhogs. The legal application of aluminum phosphide 

may vary from state to state, so dam owners should consult 

with their state wildlife agency or state pesticide registration 

board before implementing this control method. Aluminum 

phosphide comes in tablet form. Two to four tablets should 

be inserted into the main burrow and then all burrow entrances must be tightly sealed. Aluminum phosphide should 

always be used as directed on the label. 

Dam owners should consult with their state wildlife agency 

for information on state and local regulations regarding the 

use of fumigants to control groundhogs.

6.5.4 Groundhog Control Through Toxicants 

(University of Nebraska, 1994)

No toxicants are registered for groundhog control. 

6.5.5 Groundhog Control Though Frightening 

(University of Nebraska, 1994)

Scarecrows or other effigies may be installed on or around 

the earthen dam to frighten groundhogs. This method of 

control works best if the scarecrows are moved regularly 

and if there is a high level of human activity around the 

dam.
Chapter 6. Mitigating Damaging Wildlife 79

Figure 6-7. Death-Klutch 1 gopher and mole trap.

jaws

flat metal

piece

trip lever

thumb latch

body 

shaft

Figure 6-6. Victor® Gopher Getter.

6.5.6 Groundhog Control Through Repellents 

(University of Nebraska, 1994)

No repellents are registered for groundhog control. 

6.5.7 Groundhog Control Through Shooting 

(University of Nebraska, 1994)

Shooting is most effective if used as a follow-up to other 

control measures. Groundhogs are considered game animals 

in most states; therefore a hunting license may be required. 

Dam owners should consult with their state wildlife agency 

regarding specific hunting regulations and requirements. 

6.6 Pocket Gopher Management Methods

6.6.1 Pocket Gopher Control Through Habitat 

Modification (Colorado State University 

Cooperative Extension, 2003)

Removal of forbs, through either chemical or mechanical 

treatment, may control some pocket gopher damage. This 

technique is generally effective only for individuals of the 

genera Thomomys, because they prefer the underground storage structure of forbs. Other species easily survive on grass 

and therefore will not likely be deterred by this technique.

6.6.2 Pocket Gopher Control Through Trapping 

(USDA, 1994; University of Nebraska, 1994)

Trapping can be extremely effective for pocket gopher 

control in small areas or when used in conjunction with 

toxicants. There are many types of traps available for pocket 

gopher control. The Macabee® gopher trap is the most popular, but other traps are also commonly used, including the 

Victor® Gopher Getter, the Death-Klutch 1 gopher and mole 

trap, and the Guardian gopher trap (Figures 6-5 through 

6-8). Traps may be set in either the main tunnel or in one of 

the lateral tunnels (Figure 6-9). Trapping is most effective 

in the spring and fall, when gophers are pushing up new 

mounds, although it can be done year-round. Dam owners 

should consult with their state wildlife agency regarding 

specific trapping regulations.

Figure 6-5. Macabee® gopher trap.

hold-down

bar

trigger

wire

spring

bar

Figure 6-8. Guardian (California box-type) gopher trap.
80 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

Figure 6-9. Traps can be staked in lateral or main pocket gopher tunnels.

6.6.3 Pocket Gopher Control Through Fumigants 

(University of Nebraska, 1994)

Aluminum phosphide and gas cartridges are both Federally 

registered for pocket gopher control. They are generally not 

effective though because the gas moves slowly through the 

tunnel system, allowing the fumigant to diffuse through 

the soil and escape to the surface. Carbon monoxide from 

automobile exhaust has proven more effective because of its 

greater volume and pressure. To implement this method of 

control, connect a hose or pipe to the engine exhaust and 

place it in a burrow opening near a fresh soil mound. Tightly pack soil around the hose or pipe and allow the engine 

to run for at least 3 minutes. This method is generally 90% 

effective and requires no federal registration. Dam owners 

should consult with their state wildlife agency for information on state and local regulations regarding fumigants.

6.6.4 Pocket Gopher Control Through Toxicants 

(University of Nebraska, 1994)

Several rodenticides are currently registered for pocket 

gopher control. Strychnine alkaloid (0.3 to 0.5% active 

mound

lateral

main tunnel

hole dug

with shovel

Carbon monoxide is 

generally 90% effective 

for pocket gopher 

control and requires no 

Federal registration. 

ingredient) on grain baits is the most widely used. It is 

classified as a Restricted Use Pesticide and can only be sold 

to and used by a certified pesticide applicator. Applying 1 

to 2 pounds per acre of 0.3 to 0.5% strychnine alkaloid 

grain with a burrow builder should provide an 85% to 95% 

reduction in the pocket gopher population. Zinc phosphide 

(2%) is also a registered toxicant for pocket gopher control, though it is less effective than strychnine. Additionally, 
Chapter 6. Mitigating Damaging Wildlife 81

two anticoagulants (chlorophacinine and diphacinone) are 

registered for pocket gopher control. Bait can be placed in 

a pocket gopher burrow system by hand, using a special 

hand-operated bait dispenser probe or with a mechanical 

burrow builder (Figures 6-10 and 6-11). 

The first step to hand baiting with the bait dispenser is finding the main burrow, which is generally located 12 to 18 

inches away from a plugged mound. Once the main burrow 

is located, place the probe over the burrow and push down 

until there is decreased resistance on the probe. Then push 

the button on the bait dispenser to release a metered dose 

of bait. For best results, each burrow should be baited in 

two or three locations. 

Figure 6-10. Effective baiting with a bait dispenser requires 

accurately finding the pocket gopher burrow. Use the probe to 

detect the main burrow, which is usually on the plug-side of the 

mound, 8-18 inches away from the plug (USDA, 1994). 

Figure 6-11. A burrow builder mechanically dispenses bait into 

constructed burrows. Adequate soil moisture is needed to form 

effective burrows. Adequate soil can be compressed in the hand 

and rolled gently without crumbling (USDA, 1994).

Properly applied, strychnine 

alkaloid can provide an 

85% to 95% reduction in 

a pocket gopher population. 

The burrow builder is a tractor-drawn device that mechanically delivers bait underground. As the burrow builder 

moves along, it makes an artificial burrow, dispenses the bait 

into the newly formed burrow, and then closes up the hole. 

Artificial burrows should be constructed at depths similar to 

those constructed by pocket gophers in the area. 

All toxicant products should be used as directed on the 

label. Dam owners should consult with their state wildlife 

agency regarding legality of toxicant use in their state before implementing any control measures. 

6.6.5 Pocket Gopher Control Through Frightening

No frightening methods are effective for pocket gopher 

control. 

6.6.6 Pocket Gopher Control Through 

Repellents (University of Nebraska, 

1994; Witmer et al., 1995)

Repellents may be used to discourage pocket gopher inhabitation, although the effectiveness of this method is still 

in question. Initial testing has shown that some predator 

odors, such as coyote or bobcat urine, may effectively repel 
82 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

pocket gophers. Additionally, the mole plant (Euphoriba lathyrus), also known as the caper spurge or gopher purge, and 

the castor-oil plant (Ricinus lathyrus) have both been promoted 

as gopher repellents, although there is no scientific evidence 

to support this claim. Use of these plants is not recommended because they are poisonious to humans and pets, 

and can grow thickly, obscuring the dam.

6.6.7 Pocket Gopher Control Through Shooting 

(University of Nebraska, 1994)

Shooting pocket gophers is usually not a practical option 

because they spend most of their time below ground.

6.7 North American Badger Management Methods

6.7.1 North American Badger Control Through 

Habitat Modification (University of 

Nebraska, 1994; Texas Wildlife Damage 

Management Service, 1998)

Rodent control will alleviate most problems associated with 

badger damage. Badgers commonly prey on ground squirrels, pocket gophers, and prairie dogs. If this food source 

is eliminated, then damage from badger predation will be 

reduced and the badger will often move elsewhere in search 

of food. Dam owners should refer to sections of this manual 

pertaining to management of ground squirrels, pocket gophers, and prairie dogs for rodent control guidance. 

6.7.2 North American Badger Control Through 

Trapping (University of Nebraska, 1994; Texas 

Wildlife Damage Management Service, 1998)

Badgers can often be removed from an area through the 

use of cage traps, leghold traps, or snares placed near the 

entrance of an active den. Cage traps require bait, such as a 

dead chicken or large rodent. After a badger is caught alive, 

it should be euthanized or relocated to an area where it will 

not cause further damage. 

Leghold traps (No. 3 or 4) are most effective if attached to a 

drag such as a strong limb or fence post. If leghold traps are 

staked into the ground, it is likely that the badger will dig 

out the trap and escape. 

Snaring involves setting a steel-cable loop in an animal’s 

path to capture it by the neck, body, or leg. Snares are lightweight, compact, easy to set, low-cost, and they offer a high 

degree of human safety. Ready-made snares and snare components may be purchased from trapping suppliers. They 

must be attached to a solid object so the captured animal 

cannot escape. Snares should not be set where they could 

capture pets or livestock. 

Dam owners should contact their state wildlife agency regarding trapping regulations.

6.7.3 North American Badger Control Through 

Fumigants (University of Nebraska, 1994)

No fumigants are registered for badger control.

6.7.4 North American Badger Control Through 

Toxicants (University of Nebraska, 1994)

No toxicants are registered for badger control.

6.7.5 North American Badger Control Through 

Frightening (University of Nebraska, 1994)

Badgers may be discouraged from inhabiting an area if 

high-intensity lights are installed and used at night.

6.7.6 North American Badger Control Through 

Repellents (University of Nebraska, 1994)

No repellents are registered for badger control.

6.7.7 North American Badger Control Through 

Shooting (University of Nebraska, 1994)

Shooting can be an effective method of controlling small 

populations of badgers. Early morning, late evening, and 

after dark are the best times for hunting. Where legal, 

spotlights can be an effective tool for hunting at night. Dam 

owners should contact their state wildlife agency regarding 

hunting regulations and restrictions. 

6.8 Nutria Management Methods

6.8.1 Nutria Control Through Habitat Modification 

(University of Nebraska, 1994; USDA, 1991)

Nutria can be discouraged from inhabiting an area by eliminating brush, trees, thickets, and weeds, which provide food 

and cover. Cleared vegetation should be burned or removed. 

In certain situations, water level manipulation may be 

another damage control option. Dropping water levels in 
Chapter 6. Mitigating Damaging Wildlife 83

the summer and raising water levels in the winter will 

cause stress to nutria populations and may encourage them 

to relocate. The viability of this option is dependent upon 

reservoir useage (e.g., water spray, recreation, etc.) and 

owner willingness. In addition, lowering the water level has 

not yet been proven effective by researchers, but it is a tool 

to consider as part of a comprehensive nutria management 

strategy. 

6.8.2 Nutria Control Through Trapping 

(University of Nebraska, 1994)

Trapping is a very effective method of controlling nutria. 

Leghold traps are most commonly used. Most trappers 

prefer double longspring traps (No. 11 or 2), but the No. 1 

1⁄2 coilspring, No. 3 double longspring, and soft-catch fox 

traps are also effective. Traps should be set just under the 

water where an active nutria trail enters the reservoir. The 

trap should be staked to the ground just off to the side of 

the trail and covered with leaves or other debris. To increase 

effectiveness, traps should be baited with chunks of apples, 

carrots, sweet potatoes, or watermelon rinds. In deep water, 

a drowning set should be used. If a nutria is captured alive 

in shallow water, then it should be disposed of humanely. 

Single- or double-door live traps may be used to capture 

nutria. The cage should be at least 9 x 9 x 32 inches in size. 

Place the trap along active trails and bait with sweet potatoes 

or carrots. Captured nutria should be humanely destroyed.

Conibear® traps (No. 220-2, 160-2, and 330-2) are also 

commonly used to reduce nutria populations. These traps 

should be set on trails, at den entrances, in culverts, or in 

narrow waterways. They should not be used in areas frequented by children, domestic pets, or desirable wildlife 

species. 

Snaring is another option for capturing nutria. Snaring 

involves setting a steel-cable loop in an animal’s path to 

capture it by the neck, body, or leg. Snares constructed with 

3/32-inch flexible stainless steel wire or galvanized aircraft 

cable are suitable for catching nutria. They should be set 

along trails, travel routes, feeding lanes, or bank slides. 

Dam owners should contact their state wildlife agency regarding trapping regulations.

6.8.3 Nutria Control Through Fumigants 

(University of Nebraska, 1994)

No fumigants are registered for nutria control.

6.8.4 Nutria Control Through Toxicants 

(University of Nebraska, 1994)

Zinc phosphide is the only toxicant registered for nutria 

control. It is a Restricted Use Pesticide that must be purchased and applied by a certified pesticide applicator. The 

zinc phosphide is mixed with bait, such as apples, carrots, 

or sweet potatoes, and then the bait is placed in waterways, 

ponds, and ditches where permanent standing water and 

recent signs of nutria activity are found. Do not place bait 

directly in the water, but rather on floating rafts (anchored 

to the bottom or tied to the shore as depicted on figure 

6-4), small islands, floating logs, or exposed tree stumps. 

Ground baiting is not recommended because humans and 

nontarget animals may be exposed to the toxicant. 

Prebaiting increases the effectiveness of this control method. 

Apply corn oil to chunks of apples, carrots, or sweet potatoes and place the prebait at the designated baiting station. 

The station should be prebaited for several nights. Observe 

the station to ensure that nutria, rather than nontarget 

animals, are taking the bait. Once the nutria are accustomed 

to eating the prebait, the zinc-phosphide treated bait can 

be applied. The toxic bait should be applied until no more 

bait is being taken. Dead nutria that have been exposed to 

zinc phosphide should be collected and disposed of by deep 

burial or burning to prevent zinc phosphide exposure to 

domestic and wild scavengers. 

6.8.5 Nutria Control Through Frightening 

(University of Nebraska, 1994)

Harassment may temporarily deter nutria from inhabiting 

an area. Loud noises and high-pressure water sprays have 

worked in some cases. As a long-term control method, however, frightening is not an effective or practical option. 

6.8.6 Nutria Control Through Repellents 

(University of Nebraska, 1994)

No repellents are registered for nutria control. 
84 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

In certain areas, legal 

hunting with a shotgun 

or small caliber rifle 

has reduced nutria 

populations by 80%.

6.8.7 Nutria Control Through Shooting 

(University of Nebraska, 1994)

Shooting is an effective method of controlling nutria. This 

method is most effective at night with a spotlight, although 

it should be noted that this technique is not legal in all 

states. Shooting can be effective when carried out at bait 

stations, from boats, or from the bank. Dam owners should 

contact their state wildlife agency for information on hunting regulations and restrictions.

6.9 Prairie Dog Management Methods

Because other animals frequently inhabit prairie dog towns, 

including the Federally protected burrowing owl and blackfooted ferret, dam owners need to be particularly cautious 

when taking action to control prairie dogs. In regions and 

habitats where burrowing owls and black-footed ferrets are 

known to live, dam owners should coordinate with their 

state wildlife agency and the USFWS to determine whether 

either of these species is present; field surveys by qualified 

biologists may be required. Burrows that have feathers or 

white droppings at the mouth probably contain burrowing 

owls. Black-footed ferrets are secretive animals, and since it 

can be very difficult to verify their existence in a particular 

burrow system, it is best to contact the USFWS and the state 

wildlife agency for guidance on completing a black-footed 

ferret survey (University of Nebraska, 1994). If either of 

these species is present, the dam owner must contact the 

USFWS and their state wildlife agency for management 

guidance.

It is also important to remember that the Utah prairie dog, 

one of the four prairie dog species found in the United 

States, is listed as a Federally threatened species and is therefore subject to the provisions of the Endangered Species Act. 

As the name implies, the Utah prairie dog is found only 

in Utah. Dam owners in Utah who suspect that they have 

a prairie dog problem should contact the USFWS and the 

Utah Division of Wildlife Resources for species identification and management guidance.

6.9.1 Prairie Dog Control Through Habitat 

Modification (University of Nebraska, 1994)

Installation of visual barriers may discourage prairie dogs 

from inhabiting an area. Prairie dogs prefer areas of low 

vegetation to provide a clear view of their surroundings and 

to improve their ability to detect predators. Objects such 

as fences or hay bales that are strategically placed to block 

prairie dog views may reduce suitability of the habitat. 

6.9.2 Prairie Dog Control Through 

Trapping (USDA, 1991)

Trapping may be used to control prairie dogs, but it is quite 

labor intensive and therefore only practical for removing 

small populations. Cage traps for live capture, Conibear®

traps (No. 110), and leg-hold traps are often used. Cage 

traps are most effective in early spring. They should be baited with oats flavored with corn or anise oil. Dam owners 

should consult with their state wildlife agency for guidance 

on releasing captured prairie dogs. Conibear® and leg-hold 

traps should be set in burrow entrances. They do not require 

bait. Dam owners should consult with their state wildlife 

agency regarding specific trapping regulations.

6.9.3 Prairie Dog Control Through Fumigants 

(University of Nebraska, 1994)

Fumigants can be used to control prairie dogs in some situations, however this method is often costly, time-consuming, and particularly hazardous to other wildlife. Fumigation is most effective as a follow-up to toxic baits. It should 

not be used in burrows where nontarget species are thought 

to be present. 

Aluminum phosphide 

can reduce prairie 

dog populations by 

85% to 95%.

Aluminum phosphide is a registered fumigant for control of 

burrowing rodents, including prairie dogs. It is a Restricted 

Use Pesticide and therefore must be purchased and ap-
Chapter 6. Mitigating Damaging Wildlife 85

Gas cartridges can provide 

a 95% reduction in 

prairie dog populations.

Zinc phosphide can be 

75% to 85% successful 

in controlling prairie dogs 

when used correctly. 

A prebait must be applied to the burrows before the toxic 

bait. The prairie dogs will become accustomed to eating the 

non-toxic grains, which will increase the effectiveness of 

the toxic bait. The prebait and the toxic bait may be applied 

by hand or by a mechanical bait dispenser attached to an 

all-terrain vehicle, motorcycle, or horse. 

6.9.5 Prairie Dog Control Through Frightening 

(University of Nebraska, 1994)

Frightening is not an effective method of control for prairie 

dogs. 

6.9.6 Prairie Dog Control Though Repellents 

(University of Nebraska, 1994)

No repellents are Federally registered for prairie dog control.

6.9.7 Prairie Dog Control Through Shooting 

(University of Nebraska, 1994)

Continuous shooting of prairie dogs can remove about 65% 

of the population annually, but it is generally not a practical 

or cost-effective method of control. Shooting is most effective in spring because it can disrupt breeding. Dam owners 

should consult with their state wildlife agency regarding 

specific hunting regulations and requirements.

6.10 Ground Squirrel Management Methods

The northern Idaho ground squirrel, one of 23 ground 

squirrel species in the United States, is Federally listed as a 

threatened species and is therefore subject to the provisions 

of the Endangered Species Act. The northern Idaho ground 

squirrel is found in limited distribution in the northwest. 

Dam owners in that region who experience problems with 

ground squirrels should contact the USFWS and their state 

wildlife agency for species identification and management 

guidance.

plied by a certified pesticide applicator. Aluminum phosphide comes in tablet form. One tablet should be inserted 

into each burrow and then the burrow entrance should be 

tightly plugged with soil. When used correctly, aluminum 

phosphide typically provides an 85% to 95% reduction in 

prairie dog populations. The legal application of aluminum 

phosphide may vary from state to state so dam owners 

should consult with their state wildlife agency or state pesticide registration board before implementing this control 

method.

Gas cartridges may also be used to control prairie dogs. Gas 

cartridges are General Use Pesticides that can usually be 

purchased at local farm supply stores or pesticide dealers. 

When ignited, a gas cartridge will produce carbon monoxide, carbon dioxide, and other gases that are toxic to the 

prairie dog. The cartridge should be lit before it is placed in 

the burrow. Once it has been inserted, the burrow should 

be immediately plugged with soil. Gas cartridges should be 

used with caution and in accordance with the directions on 

the label. When used correctly, gas cartridges can provide a 

95% reduction in prairie dog populations. 

Dam owners should consult with their state wildlife agency 

for information on state and local regulations regarding gas 

cartridges and the use of fumigants.

6.9.4 Prairie Dog Control Through Toxicants 

(University of Nebraska, 1994)

Baiting with a toxicant is generally the most economical 

and effective method of controlling prairie dogs. Zinc phosphide bait is currently the only registered and legal toxicant 

available for prairie dog control. It is available in 2% zinc 

phosphide-treated grain bait and pellet formulations. It is a 

Restricted Use Pesticide, which means that it is only available for sale to and use by certified pesticide applicators. 

Zinc phosphide baits can be applied from July 1 through 

January 31, though it is best to apply the baits in late summer and fall when prairie dogs are most active and there is 

no green forage available. 
86 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

The New Mexico and 

Nebraska Dam Safety 

Offices have set up roosts 

in the dam environment 

to support raptors such 

as red-tailed hawks to 

provide predator control 

of small rodents.

6.10.1 Ground Squirrel Control Through 

Habitat Modification (USDA, 1991)

Routine weed control and vegetative management may limit 

some ground squirrel damage, but the effectiveness of this 

method is usually limited.

6.10.2 Ground Squirrel Control Through Trapping 

(University of Nebraska, 1994)

Trapping is a labor-intensive control method, and therefore 

it is generally only useful for removing small populations 

of ground squirrels. Jaw traps (No. 1 or No. 0), box or cage 

traps, and Conibear® traps (No. 110 or No. 110-2) may be 

used (refer to Figure 6-1). Generally, one trap is needed for 

every 10 to 15 squirrels present. Traps should be set on trails 

or near burrow entrances. Box or cage traps require bait, 

such as fruit, vegetables, peanut butter, or grain; baiting is 

not necessary with jaw traps or Conibear® traps. Dam owners should contact their state wildlife agency for information on state and local trapping regulations. 

6.10.3 Ground Squirrel Control Through Fumigants 

(University of Nebraska, 1994)

Aluminum phosphide and gas cartridges are both registered 

fumigants for ground squirrel control. Fumigants work best 

for light squirrel infestations limited to a few acres. This 

method is most effective in the spring, when ground squirrels have just emerged from hibernation. 

Aluminum phosphide is a Restricted Use Pesticide that 

comes in tablet form. This fumigant can only be purchased 

and applied by a certified pesticide applicator. One tablet 

should be placed in each burrow entrance and then the 

burrow should be plugged with soil to form an air-tight 

seal. The legal application of aluminum phosphide may vary 

from state to state so dam owners should consult with their 

state wildlife agency or state pesticide registration board 

before implementing this control method.

Gas cartridges are General Use Pesticides that can usually be 

purchased at local farm supply stores or pesticide dealers. 

When ignited, a gas cartridge will produce carbon monoxide, carbon dioxide, and other gases that are toxic to ground 

squirrels. The cartridge should be lit before it is placed in 

the burrow. Once it has been inserted, the burrow should 

be immediately plugged with soil. Gas cartridges should be 

used with caution and in accordance with the directions on 

the label. Dam owners should consult with their state wildlife agency for information on state and local regulations 

regarding gas cartridges and the use of fumigants.

6.10.4 Ground Squirrel Control Through Toxicants 

(University of Nebraska, 1994)

Zinc phosphide and two anticoagulants, chlorophacinone 

and diphacinone, are currently registered for ground squirrel control. 

When used correctly, zinc 

phosphide can result in an 

85% to 95% reduction in 

ground squirrel population. 

Zinc phosphide is a Restricted Use Pesticide, which means 

that it can only be purchased and applied by a certified 

pesticide applicator. It is a single-dose toxicant delivered on 

oat baits. The ground squirrels should be exposed to an untreated prebait several days before using the toxic grain. Bait 

can be delivered by hand or mechanically dispensed. 

Chlorophacinone and diphacinone are two anticoagulant 

baits that are registered in some states under various trade 

names. A continuous supply of bait must be applied for 4 to 

9 days for the toxicant to be effective. The bait is usually delivered in a bait box, which can be made of rubber tires or 

metal, plastic, or wood containers. The commonly used PVC 

Inverted-T anticoagulant bait station consists of 4-inch sections of plastic irrigation pipe formed into an inverted “T” 

configuration (Figure 6-12). Dam owners should contact 
Chapter 6. Mitigating Damaging Wildlife 87

their state wildlife agency for information on anticoagulants 

that may be available for use.

All products should be used as directed. Dam owners should 

consult with their state wildlife agency regarding legality of 

toxicant use in their state.

6.10.5 Ground Squirrel Control Through Frightening 

(University of Nebraska, 1994)

Frightening is not an effective method of control for 

ground squirrels.

6.10.6 Ground Squirrel Control Through Repellents 

(University of Nebraska, 1994)

No repellents are registered for ground squirrel control.

6.10.7 Ground Squirrel Control Through Shooting 

(University of Nebraska, 1994)

Shooting may be used to remove small populations of 

ground squirrels, although it is an expensive and time-consuming method of control. Dam owners should consult 

with their state wildlife agency regarding specific hunting 

regulations and requirements

6.11 Armadillo Management Methods

6.11.1 Armadillo Control Through Habitat 

Modification (University of Nebraska, 1994)

It is possible to discourage armadillos from burrowing in an 

earthen dam by implementing the following habitat mitigation techniques:

Remove brush or other cover to reduce the amount of 

suitable habitat.

Apply soil insecticides to remove insects and other invertebrates that make up the majority of the armadillo’s diet. 

6.11.2 Armadillo Control Through Trapping 

(University of Nebraska, 1994)

Trapping can be an effective method of managing armadillos. Live or box traps (10 x 12 x 32-inch), such as the 

Havahart or Tomahawk, work best. A trap’s effectiveness can 

be enhanced by adding “wings” (1 x 4-inch or 1 x 6-inch 

boards about 6 feet long) to funnel the animal into the trap 

(Figure 6-13). The best locations to set traps are along pathways to burrows and along fences or other barriers where 

armadillos may travel. Conibear® (No. 220) or leghold 

traps (No. 1 or 2) may also be used (refer to Figure 6-1). 

These types of traps should be placed at the entrance of a 

burrow.

•

•

Figure 6-13. The effectiveness of cage traps can be enhanced 

by adding “wings” to funnel the armadillo into the trap.

12” to 15”

24” to 30”

45°

PVC (4”) T 

4”

Figure 6-12. The PVC Inverted-T bait station delivers 

anticoagulant bait to ground squirrels. 
88 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

6.11.7 Armadillo Control Through Shooting 

(University of Nebraska, 1994)

Shooting is an effective method of controlling armadillos. The best time to shoot is during twilight hours or at 

night when armadillos are most active. Dam owners should 

consult with their state wildlife agency regarding specific 

hunting regulations and requirements. 

6.12 Livestock (Cow, Sheep, Horse, Pig, and 

Wild Pig) Management Methods

6.12.1 Livestock Control Through Habitat 

Modification (USDA, 1991)

Providing a water source away from the earthen dam may 

help reduce livestock damage near the dam, since livestock 

are often at the dam in search of drinking water.

6.12.2 Livestock Control Through Trapping (USDA, 

1991; University of Nebraska, 1994)

Trapping is quite effective for wild pigs. Stationary corraltype traps and box traps are commonly used (Figure 6-14). 

They are most effective in summer when acorns and other 

Figure 6-14. Stationary hog trap.

2” x 4” x 24’ wood

36” x 48” x 3/4” plywood

36’ x 2” x 4” mesh welded wire

4 6” strap hinges

2 12” screen door springs

8 6” steel fence posts

4 lbs 16-penny nails

1 lbs 12-penny nails

2 lbs 1 1/2” staples

1 100 12-gauge wire

6”

2” x 4” mesh welded 

wire (12 gauge)

steel fence post

spring 18”

48”

front

48”

side

96”

6.11.3 Armadillo Control Through Fumigants 

(University of Nebraska, 1994)

No fumigants are Federally registered for armadillo control. 

However, there are some fumigants that are effective and 

that may be legal in certain states. Dam owners should consult their state wildlife agency regarding fumigants that may 

be legal in their area.

6.11.4 Armadillo Control Through Toxicants 

(University of Nebraska, 1994)

No toxicants are registered for armadillo control.

6.11.5 Armadillo Control Through Frightening

Frightening is not an effective method of armadillo control.

6.11.6 Armadillo Control Through Repellents 

(University of Nebraska, 1994)

No repellents are registered for armadillo control.
Chapter 6. Mitigating Damaging Wildlife 89

preferred natural foods are not available. Traps should be 

baited with grains, fruits, or vegetables. The traps may be 

placed anywhere that wild pigs concentrate.

6.12.3 Livestock Control Through 

Fumigants (USDA, 1991)

Fumigants are not suitable for livestock control.

6.12.4 Livestock Control Through 

Toxicants (USDA, 1991) 

Toxicants are not suitable for livestock control.

6.12.5 Livestock Control Through 

Frightening (USDA, 1991)

Frightening devices such as animated scarecrows or firecrackers may temporarily deter livestock from inhabiting an 

area, but these techniques generally do not provide a longterm solution to livestock damage. 

6.12.6 Livestock Control Through 

Repellents (USDA, 1991)

Repellents are not suitable for livestock control.

6.12.7 Livestock Control Through 

Shooting (USDA, 1991)

Shooting may be an effective method of removing a small 

population of nuisance livestock; however, hunting is generally only permitted for wild animals such as pigs. Dam 

owners should contact their state wildlife agency regarding 

hunting regulations and restrictions. 

6.13 Crayfish Management Methods

6.13.1 Crayfish Control Through Habitat Modification 

(Virginia Cooperative Extension, 2001a).

Damage may be prevented by stocking the reservoir with 

natural enemies of crayfish, such as trout, bass, catfish, and 

large bluegills. These species will eat the crayfish, which 

will reduce the overall crayfish population and decrease the 

number of burrows. 

6.13.2 Crayfish Control Through Trapping 

(University of Nebraska, 1994)

Wire cage traps baited with fish or meat can be used to 

catch crayfish. 

6.13.3 Crayfish Control Through Fumigants 

(University of Nebraska, 1994)

No fumigants are Federally registered for crayfish control. 

6.13.4 Crayfish Control Through Toxicants 

(University of Nebraska, 1994)

No toxicants are Federally registered for crayfish control. 

Some states, however, have regulations that allow application of certain insecticides for crayfish burrow treatment. 

Dam owners should consult with their state wildlife agency 

regarding the legality of toxicants in their state. 

6.13.5 Crayfish Control Through Frightening

Frightening is not an effective method of controlling crayfish.

6.13.6 Crayfish Control Through Repellents 

(University of Nebraska, 1994)

No repellents are registered for crayfish control.

6.13.7 Crayfish Control Through Shooting

Shooting is not a suitable method of controlling crayfish.

6.14 Coyote Management Methods

6.14.1 Coyote Control Through Habitat 

Modification (USDA, 1991)

Proper vegetative management (mowing and brush removal) and rodent control will often discourage coyotes from 

digging in earthen dams. 

6.14.2 Coyote Control Through Trapping 

(University of Nebraska, 1994)

Steel leg-hold traps (No. 3 and 4) are often used for coyote removal. Effective use of these traps for coyote control 

generally requires a great deal of experience and training. 
90 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

Dam owners should contact their state wildlife agency for 

guidance on trapping nuisance coyotes. 

Snaring is another method of removing coyotes. Snaring 

involves setting a steel-cable loop in an animal’s path to 

capture it by the neck, body, or leg. Snares are light-weight, 

compact, easy to set, low-cost, and they offer a high degree of human safety. In one study, they were proven to 

be more effective than leg-hold traps for coyote control. 

Snares are usually made of a 2.5- to 10-foot long piece of 

galvanized aircraft cable with a slide lock that forms a loop. 

Snares should be set along known coyote trails. They must 

be attached to a solid object so that the captured animal 

cannot escape. Snares should not be set where they could 

capture pets or livestock. Snares are not legal in all states so 

dam owners should consult with their state wildlife agency 

before choosing this control method. Once caught, coyotes 

should be humanely destroyed.

6.14.3 Coyote Control Through Fumigants 

(University of Nebraska, 1994)

Gas cartridges are the only registered fumigant for coyote 

control. Gas cartridges are General Use Pesticides that can 

usually be purchased at local farm supply stores or pesticide 

dealers. When ignited and placed in the den, a gas cartridge 

will produce carbon monoxide, carbon dioxide, and other 

gases that are toxic to the coyote. Gas cartridges should be 

used with caution and in accordance with the directions 

on the label. Dam owners should consult with their state 

wildlife agency regarding state and local regulations on gas 

cartridges and the use of fumigants.

6.14.4 Coyote Control Through Toxicants 

(University of Nebraska, 1994)

The only toxicant registered for coyote control is sodium 

cyanide used in an M-44 ejector device. The M-44 is a 

spring-activated device that expels a sodium cyanide capsule into the animal’s mouth. The M-44 device should be 

set along the sides of trails or paths used by coyotes. This 

control method is most effective during cooler months. The 

M-44 sodium cyanide device is classified as a Restricted Use 

Pesticide and may only be used by USDA Animal Damage 

Control personnel and, in some states, certified pesticide 

applicators. The M-44 is not registered for use in all states so 

dam owners must consult their state wildlife agency before 

implementing this control measure. 

6.14.5 Coyote Control Through 

Frightening (USDA, 1991)

Several types of frightening devices are available for coyote 

control, but these devices were designed for livestock protection and are not practical for protection of earthen dams.

6.14.6 Coyote Control Through Repellents 

(University of Nebraska, 1994)

No repellents have proven effective for coyote control.

6.14.7 Coyote Control Through 

Shooting (USDA, 1991)

Coyote hunting is often an effective method of control for 

livestock protection, but it is generally not practical for 

protecting earthen dams. If a dam owner decides to pursue 

this method of control, they must contact the state wildlife 

agency for information on hunting regulations. 

6.15 Mole and Vole Management Methods

6.15.1 Mole and Vole Control Through 

Habitat Modification (University of 

Nebraska, 1994; USDA, 1991)

It is possible to discourage moles from burrowing in an 

earthen dam by implementing the following habitat modification techniques:

Compact the soil with a roller to reduce soil moisture. 

This will reduce the habitat’s attractiveness to moles.

Apply insecticides to reduce food supply. Legal insecticides may vary by state so dam owners should contact 

their state wildlife agency for specific guidance. 

6.15.2 Mole and Vole Control Through Trapping 

(University of Nebraska, 1994) 

Trapping is the most effective method of reducing mole 

populations. Several traps are specifically designed for 

moles, including the Victor mole trap, Out O’ Sight, and 

Nash (choker loop) mole trap. If used properly, any of these 

traps can be effective. Traps should be set in the surface runway where there is evidence of recent mole activity.

Trapping is generally not an effective method of reducing large vole populations because of prohibitive time and 

•

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Chapter 6. Mitigating Damaging Wildlife 91

labor costs. Mouse snap traps may be used for control of a 

few individual voles. Traps should be set perpendicular to a 

runway with the trigger end in the runway. Voles are easiest 

to trap in the fall and late winter. 

6.15.3 Mole and Vole Control Through Fumigants 

(University of Nebraska, 1994)

Both aluminum phosphide and gas cartridges are Federally registered for mole control. Aluminum phosphide is 

a Restricted Use Pesticide that comes in tablet form. One 

tablet should be placed in each burrow entrance and then 

the burrow should be plugged with soil to form an air-tight 

seal. The legal application of aluminum phosphide may vary 

from state to state so dam owners should consult with their 

state wildlife agency or state pesticide registration board 

before implementing this control method.

Gas cartridges are General Use Pesticides that can usually be 

purchased at local farm supply stores or pesticide dealers. 

When ignited, a gas cartridge will produce carbon monoxide, carbon dioxide, and other toxic gases. The cartridge 

should be lit before it is placed in the burrow. Once it has 

been inserted, the burrow should be immediately plugged 

with soil. Gas cartridges should be used with caution and 

in accordance with the directions on the label. Dam owners 

should consult with their state wildlife agency for information on state and local regulations regarding gas cartridges 

and the use of fumigants.

Fumigants are generally not effective for vole control. The 

vole burrow system is so complex and shallow that the 

fumigant easily escapes to the surface.

6.15.4 Mole and Vole Control Through Toxicants 

(University of Nebraska, 1994)

Strychnine alkaloid and chlorophacinone are both Federally 

registered for mole control. Strychnine alkaloid is a Restricted Use Pesticide that can only be purchased and applied by 

a certified pesticide applicator. However, since moles do not 

normally consume grain, strychnine alkaloid grain baits are 

seldom effective. Chlorophacinone is commercially available 

in pellet form under the name Orco Mole Bait. Researchers 

have found that this is a highly effective and easy to apply mole control technique. Dam owners should be aware, 

though, that two or more successive treatments are often 

required. If a dam owner chooses either of these methods 

of control, they should contact the state wildlife agency 

regarding the legality of toxicant use in their state.

Zinc phosphide is often used for vole control. Zinc phosphide is a single-dose toxicant available in pellet or grain 

bait formulas. Pellets or grain bait can be delivered to burrows by hand or mechanically dispensed. Zinc phosphide is 

a Restricted Use Pesticide, which must be purchased and applied by a certified pesticide applicator. Anticoagulant baits 

can also be used to reduce vole populations. Anticoagulants 

generally require several feedings and can take anywhere 

from 5 to 15 days to be effective. Bait can be delivered by 

hand, mechanically dispensed, or placed in various types 

of bait containers. Registration for anticoagulants varies by 

state.

All products should be used as directed. Dam owners should 

consult with their state wildlife agency regarding legality of 

toxicant use in their state.

6.15.5 Mole and Vole Control Through Frightening 

(University of Nebraska, 1994)

Frightening is not an effective method of control for moles 

or voles.

6.15.6 Mole and Vole Control Through Repellents 

(University of Nebraska, 1994)

No repellents are registered for mole control.

Several repellents using thiram or capsaicin as the active 

ingredient are registered for vole control, but there is no 

evidence that these repellents are actually effective. Dam 

owners should contact their state wildlife agency or pesticide regulatory agency for information on available repellents in their state. 

6.15.7 Mole and Vole Control Through Shooting 

(University of Nebraska, 1994)

Shooting is not an effective method of control for moles or 

voles.

6.16 River Otter Management Methods

6.16.1 River Otter Control Through Habitat 

Modification (University of Nebraska, 1994)

Habitat modification is generally not an effective method 

of control for river otters. Otters often share their environment with beavers, whose burrowing activity is detrimental 

to the earthen dam environment. Otters will often live in 
92 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

beaver burrows and dens and do not often dig their own 

dens. Before mitigating for the river otter, evaluate whether 

the damaging actions are caused by beaver so that the appropriate species is managed and proper preventive actions 

are implemented (as discussed in Chapters 4.0 and 5.0 of 

this manual).

6.16.2 River Otter Control Through Trapping 

(University of Nebraska, 1994)

Both Conibear (No. 220 and 330) and leghold (modified 

No. 1 1⁄2 soft-catch and No. 11 double coilspring) traps have 

been successfully used to catch river otters. Traps should 

be placed underwater along river otter trails or on “pullouts” where otters leave the water. Leghold traps can also be 

used out of the water along trails and peninsula crossings. 

River otter trapping is illegal in many states so dam owners 

should contact their state wildlife agency before initiating a 

trapping program. 

6.16.3 River Otter Control Through Fumigants 

(University of Nebraska, 1994)

No fumigants are registered for river otter control.

6.16.4 River Otter Control Through Toxicants 

(University of Nebraska, 1994)

No toxicants are registered for river otter control.

6.16.5 River Otter Control Through Frightening 

(University of Nebraska, 1994)

Frightening has not proven to be an effective method of 

river otter control.

6.16.6 River Otter Control Through Repellents 

(University of Nebraska, 1994)

No repellents are registered for river otter control.

6.16.7 River Otter Control Through Shooting 

(University of Nebraska, 1994)

Shooting is generally only effective for removing small 

populations of river otters. Dam owners should contact their 

state wildlife agency for information on hunting regulations 

and requirements. 

6.17 Gopher Tortoise Management Methods

The gopher tortoise is a Federally listed threatened species and therefore subject to the provisions of the Endangered Species Act. The historic range of the gopher tortoise 

includes Alabama, Florida, Georgia, Louisiana, Mississippi, 

and South Carolina. Dam owners in those states who suspect 

that they have a gopher tortoise problem should contact 

the USFWS and their state wildlife agency for management 

guidance.

6.17.1 Gopher Tortoise Control Through Habitat 

Modification (University of Nebraska, 1994)

Habitat modification is generally not an effective method of 

gopher tortoise control.

6.17.2 Gopher Tortoise Control Through Trapping

Since the gopher tortoise is Federally listed as a threatened 

species, dam owners should contact the USFWS or their 

state wildlife agency for management guidance. 

6.17.3 Gopher Tortoise Control Through Fumigants 

(University of Nebraska, 1994)

No fumigants are registered for gopher tortoise control.

6.17.4 Gopher Tortoise Control Through Toxicants 

(University of Nebraska, 1994)

No toxicants are registered for gopher tortoise control.

6.17.5 Gopher Tortoise Control Through Frightening

Frightening has not proven to be an effective method of 

gopher tortoise control and would be prohibited under the 

Endangered Species Act.

6.17.6 Gopher Tortoise Control Through Repellents 

(University of Nebraska, 1994)

No repellents are registered for gopher tortoise control.

6.17.7 Gopher Tortoise Control Through Shooting 

(University of Nebraska, 1994)

Gopher tortoises are protected under the Endangered Species Act and therefore, cannot be shot. Dam owners should 
Chapter 6. Mitigating Damaging Wildlife 93

contact the USFWS or their state wildlife agency for management guidance. 

6.18 Red Fox and Gray Fox Management Methods

6.18.1 Red Fox and Gray Fox Control 

Through Habitat Modification

Proper vegetative management (mowing and brush removal) and rodent control will often discourage foxes from 

digging in earthen dams by reducing their primary food 

source.

6.18.2 Red Fox and Gray Fox Control Through 

Trapping (University of Nebraska, 1994)

Trapping is a very effective method of controlling foxes, 

however it requires a great deal of expertise and training. 

Steel leg-hold traps (No. 1 1⁄2, 1 3⁄4, and 2 doublespring coil 

traps; and No. 2 and 3 double longspring trap) are suitable 

for both red and gray foxes. Cage traps may be used for juvenile red foxes. Traps set along trails, at entrances to fields, 

and near bait carcasses are most effective. 

Snares may also be used to capture foxes. Snaring involves 

setting a steel-cable loop in an animal’s path to capture it by 

the neck, body, or leg. Snares should be made from 1/16-

inch, 5/64-inch or 3/32-inch cable to capture red or gray 

foxes. The snare should have a 6-inch loop that is placed 10 

to 12 inches off the ground. Snares should be set on trails 

or in crawl holes that are frequented by foxes. 

Traps and snares are not legal in all states. Dam owners 

should contact their state wildlife agency for specific information on trapping regulations.

6.18.3 Red Fox and Gray Fox Control Through 

Fumigants (University of Nebraska, 1994)

Gas cartridges are the only registered fumigant for red and 

gray fox control. Gas cartridges are General Use Pesticides 

that can usually be purchased at local farm supply stores or 

pesticide dealers. When ignited and place in the den, a gas 

cartridge will produce carbon monoxide, carbon dioxide, 

and other gases that are toxic to the fox. Gas cartridges 

should be used with caution and in accordance with the 

directions on the label. Dam owners should consult with 

their state wildlife agency for information on state and local 

regulations regarding gas cartridges and the use of fumigants.

6.18.4 Red Fox and Gray Fox Control Through 

Toxicants (University of Nebraska, 1994)

The only toxicant registered for red and gray fox control is 

sodium cyanide used in an M-44 ejector device. The M-44 

is a spring-activated device that expels a sodium cyanide 

capsule into the animal’s mouth. It should be set along trails 

and at crossings regularly used by foxes. This is a Restricted 

Use Pesticide and may only be used by USDA Animal Damage Control personnel and, in some states, certified pesticide applicators. The M-44 is not registered in all states so 

dam owners must consult their state wildlife agency before 

implementing this control measure.

6.18.5 Red Fox and Gray Fox Control Through 

Frightening (University of Nebraska, 1994)

Noise-making devices such as radios, amplifiers, or propane 

exploders may temporarily deter foxes from inhabiting an 

area, but they do not provide a long-term solution.

6.18.6 Red Fox and Gray Fox Control Through 

Repellents (University of Nebraska, 1994)

No repellants are registered for red or gray fox control. 

6.18.7 Red Fox and Gray Fox Control 

Through Shooting

Shooting is another method of managing both red and gray 

foxes. Hunting regulations and seasons vary by state. Dam 

owners should contact their state wildlife agency for specific 

information on hunting foxes.

6.19 Canada Goose Management Methods

6.19.1 Canada Goose Control Through Habitat 

Modification (Virginia Cooperative Extension, 

2001b; University of Nebraska, 1994)

The following habitat modification techniques can be 

implemented to reduce Canada goose damage:

Minimize the amount of forage plants that exists near the 

water body by mowing or hand removal.

Construct a wire grid of stainless steel spring wire or 

monofilament line above the surface of the water. This 

will prevent Canada geese and other waterfowl from using the water and discourage them from nesting in that 

•

•
94 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

area. The individual lines should be staked to the ground 

about 12 inches above the water’s surface. 

6.19.2 Canada Goose Control Through Trapping 

(University of Nebraska, 1994; Virginia 

Cooperative Extension, 2001b)

Live trapping may be effective for small populations of 

Canada geese. Several types of traps are effective including 

walk-in funnel traps, rocket or cannon nets, and springpowered nets. A federal permit is required before trapping 

may be initiated. In addition, all relevant state and federal 

agencies must agree on what will happen to the geese after 

capture. Dam owners should contact the USFWS and their 

state wildlife agency for guidance.

Walk-in funnel traps are most effective in late June or early 

July. These types of traps can be constructed using poultry 

wire, woven wire fencing, steel fence posts, and netting 

(Figure 6-15). The trap should be set immediately next to 

the affected waterbody and then the geese should be herded 

into the trap. The herders must surround the geese on three 

sides, forcing them into the trap. Once the geese are secured 

in the trap, they may be transported to a designated location.

Net traps may also be used to capture Canada geese. Rocket 

or cannon nets with 2- to 2.5-inch mesh work well for 

large geese. The net should be placed at a location near the 

water and a second site should be repetitively baited with 

corn or other suitable bait until the bait is well accepted. 

Once the geese are trained to feed at the bait site, the area 

should be re-baited in preparation for capture. When the 

geese are concentrated at the site, the rocket or cannon 

net should be fired at the location so the birds are trapped 

underneath. The Canada geese can then be transported to a 

designated location. Spring-powered nets work in a similar 

fashion, though they are smaller than standard rocket or 

cannon nets. The net is triggered mechanically or electronically, and because it does not create as much noise as the 

rocket or cannon net, it may be more effective even though 

it is smaller. 

A final method of capturing Canada geese is through the 

use of an immobilizing agent, Alpha-chloralose. Alpha-chloralose is a non-lethal chemical that is applied to bait and 

then fed to the geese. Approximately 20 to 90 minutes after 

ingestion, the geese will be unable to fly or escape and can 

be captured by hand. Alpha-chloralose may only be used 

by USDA Animal Damage Control (ADC) staff or biologists of other certified state or federal wildlife management 

agencies. Dam owners should contact USDA ADC staff, the 

USFWS, or their state wildlife agency for more information 

about this option 

6.19.3 Canada Goose Control Through Fumigants

Fumigants are not a practical method of control for Canada 

geese. 

6.19.4 Canada Goose Control Through Toxicants 

(University of Nebraska, 1994)

No toxicants are registered for Canada goose control.

6.19.5 Canada Goose Control Through Frightening 

(Virginia Cooperative Extension, 2001b)

Auditory and visual scare devices may be used to deter 

Canada geese from inhabiting an area. Auditory scare devices make loud noises that will frighten geese away. Commonly used devices include propane cannons, pyrotechnics, 

and pre-recorded tapes of Canada goose distress calls. Visual 

scare devices installed on or around an earthen dam are also 

effective. They are usually inexpensive and easy to install, 

Figure 6-15. Canada goose funnel trap. but they work best in conjunction with another deterrent. 

Holding pen

5’ welded 

turkey-wire

15’ to 20’ square

Funnel opening 75’ to 100’

Space steel fence posts every

20’ to 30’ along wings 

as needed for support

Trap wings

 3’ chicken wire

 50’ to 100’ long

Install steel fence 

posts as needed 

for support
Chapter 6. Mitigating Damaging Wildlife 95

6.20.1 American Alligator Control Through Habitat 

Modification (University of Nebraska, 1994)

Removal of emergent wetland vegetation may reduce alligator densities by reducing cover. There are strict laws however, regarding human modifications to wetlands so dam 

owners must consult with appropriate state environmental 

agencies before disturbing any wetland vegetation. 

6.20.2 American Alligator Control Through 

Trapping (University of Nebraska, 1994)

Trapping is an effective method of eliminating alligators 

from an area. A baited hook is the simplest and most effective method. This involves rigging a large fish hook (12/0 

forged) with bait (e.g., fish, beef, chicken, or nutria) and 

suspending it via rope from a tree or pole about 2 feet 

above the water. When the alligator swallows the bait, the 

hook is lodged in its stomach and the alligator is retrieved 

using the attached rope. This method almost always kills or 

injures the alligator. 

Trip-snare traps and wire box traps may also be used. They 

are not quite as effective as the baited hook, but they do 

not kill or injure the alligator, which then must be relocated. Dam owners must contact the USFWS and their state 

wildlife agency for information on trapping regulations, the 

Endangered Species Act, and permit requirements.

6.20.3 American Alligator Control Through 

Fumigants (University of Nebraska, 1994)

No fumigants are registered for alligator control.

6.20.4 American Alligator Control Through 

Toxicants (University of Nebraska, 1994)

No toxicants are registered for alligator control.

6.20.5 American Alligator Control Through 

Frightening (University of Nebraska, 1994)

Under the Endangered Species Act, no actions to harass or 

frighten a protected species are allowed.

6.20.6 American Alligator Control Through 

Repellents (University of Nebraska, 1994)

No repellents are registered for alligator control.

Examples of visual scare devices include strobe lights, scarecrows, owl effigies, mylar reflective tape, flags, and balloons. 

Harassment or hazing of Canada geese is generally more 

effective than visual or auditory deterrents, but it can be 

labor intensive and expensive. Examples of common hazing 

programs include use of radio-controlled toys (boats or 

airplanes), trained dogs, or high-power water spray devices. 

These deterrent activities must be persistent and repeated to 

remain effective. 

6.19.6 Canada Goose Control Through Repellents 

(Virginia Cooperative Extension, 2001b)

Methyl anthranilate has been registered as a goose repellant under the name ReJeX-iT. This repellant is non-toxic 

and does not harm the geese. Re-JeX-iT is applied directly 

to the grass of an affected area. It may have to be reapplied 

frequently to remain effective. Repellents should always be 

used as directed. 

6.19.7 Canada Goose Control Through Shooting 

(University of Nebraska, 1994)

Hunting is another effective method of reducing Canada 

goose populations. Since Canada geese are listed as migratory birds under the Migratory Bird Treaty Act, a federal 

permit is required. In many areas, state permits are also 

required for hunting Canada geese. Dam owners should 

contact the USFWS and their state wildlife agency for specific hunting regulations and requirements. 

6.19.8 Other Methods of Canada Goose Control

It is also possible to reduce resident Canada goose populations by oiling, shaking, or puncturing their eggs. This requires a federal permit; dam owners should contact USFWS 

and their state wildlife agency for more information. 

6.20 American Alligator Management Methods

The American Alligator is Federally listed as a threatened 

species “due to similarity of appearance” to the federally endangered American crocodile. This listing grants the 

American Alligator protection under the Endangered Species 

Act. Dam owners who experience problems with nuisance 

alligators should contact the USFWS and their state wildlife 

agency for management guidance. 
96 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

6.20.7 American Alligator Control Through 

Shooting (University of Nebraska, 1994)

Shooting is an effective method of eliminating alligators. 

A sufficiently powerful rifle (.243 caliber or larger) should 

be used for a humane kill. Dam owners must contact the 

USFWS and their state wildlife agency for information on 

hunting regulations, compliance with the Endangered Species Act, and permit requirements.

6.21 Ant Management Methods

6.21.1 Ant Control Through Habitat Modification 

(University of Georgia Cooperative 

Extension Service, 2000)

It may be possible to reduce ant populations by physically 

destroying visible ant mounds. This can be accomplished by 

simply knocking down or disturbing mounds with a stick 

or shovel. Another option is to pour very hot (almost boiling) water directly on each mound. 

Insecticides can 

contaminate both ground 

and surface waters so 

dam owners need to be 

particularly cautious when 

applying baits or chemical 

treatments near a reservoir. 

Insecticide use must occur 

in accordance with Federal 

law (FIFRA of 1996).

Pouring very hot water 

on each ant mound 

will eliminate about 

60% of mounds. 

6.21.4 Ant Control Through Toxicants (University of 

Florida Cooperative Extension Service, 2002)

Ants can usually be controlled with baits or chemical treatments. Many of these products are available commercially at 

hardware stores, home and garden suppliers, and other retail outlets. These treatments come in various forms, including granules, liquids, gels, and ready-to-use tamper resistant 

containers. Treatment should be tailored to the type of ant 

species present and the extent of infestation. Dam owners 

should contact their local cooperative extension agency or 

a professional pest control company for assistance. Professional pest control companies may also be able to provide 

stronger treatment options if damage is significant and the 

use of commercially available products is not effective. 

6.21.2 Ant Control Through Trapping

Ant traps are commercially available, but they are not effective for large, outdoor ant infestations.

6.21.3 Ant Control Through Fumigants (University 

of Georgia, 1993; University of Georgia 

Cooperative Extension Service, 2000)

Fumigants may help control some type of ant species. 

Earthfire® (vaporized resmethrin) and Brom-O-Gas (methyl 

bromide) are two examples of fumigants that have proven 

effective against fire ants. Both are Restricted Use Pesticides 

that must be purchased and applied by a certified pesticide 

applicator. These fumigants may not necessarily be effective 

for all ant species. Dam owners should contact a professional pest removal company for information on fumigants that 

may be effective for their particular ant infestation. 

6.21.5 Ant Control Through Frightening

Frightening is not an effective or practical method of ant 

control.

6.21.6 Ant Control Through Repellents

Large, outdoor ant infestations cannot be effectively controlled through the use of repellents.

6.21.7 Ant Control Through Shooting

Shooting is not a practical method of ant control.
Chapter 7. Fiscal Considerations For Managing Animal Damage On Earthen Dams 97

“There is no free lunch. Either we make the investments required to keep our 

nation’s dams safe, or we will pay the price in dam failures.”

Martin McCann, consulting professor of civil and environmental engineering at Stanford 

University and director of the National Performance of Dams Program (NPDP). 

7.0 Fiscal Considerations 

for Managing Animal 

Damage on Earthen Dams

Almost everyone in the dam community agrees that the 

funds spent preserving a dam’s integrity and safe operation will almost always be less than those spent repairing 

an unsafe dam or worse, recovering from a dam failure. The 

economics behind this understanding are self-explanatory 

and probably need no quantitative explanation; yet across 

the nation, dams deteriorate from animal intrusion damages 

and dam owners struggle with the financial responsibility 

of repairing their unsafe dams, or removing them altogether 

when the repair costs become too great. Clearly then, the 

economic considerations related to appropriate dam management go beyond the economic efficiency and long-term 

benefit of such repairs; the considerations involve acknowledgement of animal damages as a problem, human motivation factors, and the availability of funding mechanisms at 

the federal and state level.

7.1 Fiscal Considerations for the 

Reluctant Dam Owner

As indicated in the FEMA/ASDSO workshops, inspectors, 

engineers, and regulators can find it difficult to convince 

dam owners that animal burrows and erosion can have 

serious detrimental effects on their dams. Even though dam 

failures are becoming all too common—partially a product 

of America’s aging dams—some dam owners put too much 

confidence in the integrity of their dams, even when visible 

evidence of animal burrows and inappropriate vegetation 

are present on their dams. For these dam owners, animal 

damage management is not likely to become a budget line 

item until an understanding is developed of how adverse 

animal intrusion effects can cascade, resulting in extensive 

repair/replacement costs, as well as the associated liabilities, 

that follow a dam failure. 

7.2 Fiscal Considerations of the Willing Dam Owner

Other dam owners are aware of the dangers inherent to 

animal damages at an earthen dam, but overlook routine 

owner actions that are relatively affordable and can save 

hundreds of thousands of dollars in the long-term, not to 

mention reduce the public safety hazard for those located 

downstream of the dam. Inspections and repair actions are 

indeed overlooked, as documented by the states in the 2003 

surveys and in the 2002 workshop where “financial limitations by owners” is listed as the most common impediment 

to timely and adequate dam upkeep. Considering that over 

50% of the dams in this country are privately owned (AS-
98 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

comes to the upkeep of their dams. Economic impacts of a 

failed dam can include:

Liability Costs of Loss of Life and Property Damage. Liability may be imposed on a dam owner if maintenance, 

repair, or operations were conducted in an unsafe or 

improper manner. Liability could apply to the dam owner 

as well as the company who possesses the dam and the individual who or company which operates and maintains the 

dam. The dam owner must take actions to ensure the dam 

functions properly so that injuries to people or property are 

avoided. This applies to foreseeable conditions or circumstances that can be predicted with reasonable certainty. If an 

inspection identifies problems at the dam, then an owner 

should correct them (Pennsylvania DEP, 1995). 

Clean-up Costs. The costs associated with clean-up from a 

dam failure can be tremendous, depending on the size of 

the reservoir and the amount of downstream development. 

Debris removal, sediment clean-up, and reconstruction of 

damaged infrastructure could be required. 

Loss of Dam Infrastructure and Its Revenue. Over 30% of 

the dams in the United States are used primarily for recreation (ASDSO, 2003). The benefit of dams to recreational 

income to the community can be in the millions of dollars 

each year, depending on the reservoir size and recreational 

opportunities available. 

Environmental Losses. Many reservoirs provide wildlife 

habitat and associated ecotourism revenue, which generates $59 billion annually in the United States. Communities 

often benefit from the “wilderness” which dams and their 

reservoirs provide. 

Economic Effect on Community. A community that 

depends on the dam for several uses (e.g., flood control, 

irrigation, water supply) will have to locate other facilities 

to serve these purposes should the dam fail or be removed. 

Alternative sources could be costly or may not be available 

as quickly as needed, resulting in an adverse social and economic impact on the community. 

In essence, a neglected dam can cause a cascade of adverse 

effects at the community level as well as result in liability issues for the dam owner. Attaching a reasonable dollar figure 

to each of the considerations above would illustrate that this 

considerable investment per year in maintenance is like paying an insurance premium that covers the dam owner and 

their community. 

Vegetation Management

(mowing twice per year)

$500 to $1000 annually*

Owner Inspection (one to

two times per year)

No cost for dam owner inspection;

inspection once every 2 to 5 years

by a Professional Engineer can cost

between $3,500 and $7,500

Filling animal burrows

(per burrow)

$100 to $300 depending upon

burrow size and repair method (grout

or excavate and replace)

*for most dams, as indicated in FEMA, 2002.

This estimate assumes the dam is in good condition and that

the owner is providing upkeep of an already stable operation

Table 7.1

DSO, 2003), financial limitations to upkeep pose a daunting 

threat to public safety. 

Still other dam owners know the inherent problems of 

animal damage, and vigilantly conduct inspections, mow 

twice annually, and fill burrows in a timely manner. However, some dams because of their size, location, and biological attractiveness continue to have animal damage problems 

despite owner vigilance. In these cases, the dam owner pays 

continuously to correct animal damages and routine owner 

actions become an expensive proposition in terms of both 

time and money. 

7.3 Overcoming the Economic Hurdles

The current and persisting economic issues with regard to 

animal damage management at earthen dams is twofold: 

first, reluctant owners need to be educated on the dangers 

of animal damages and motivated by economic examples; 

and second, funding sources for all owners need to be identified to assist funding of needed repairs. To begin to address 

the first consideration, a simple estimate of routine dam 

maintenance as it relates to vegetation and animal management (one influences the other) is given below: 

As the table indicates, the cost of routinely maintaining a 

dam is estimated at greater than $500.00 dollars per year. 

For many private dam owners, such as businesses and 

citizens, the outlay of these funds, though relatively low, 

is prohibitive. Even those dam owners with substantial 

financial resources are often overwhelmed by the costs of 

dam maintenance and repairs (WaterWebster, 2003). In 

these cases, it is important for dam owners to consider that 

neglect will eventually lead to greater costs on many levels; 

in short, dam owners can’t afford to save money when it 
Chapter 7. Fiscal Considerations For Managing Animal Damage On Earthen Dams 99

Lessons Learned:

Maintenance of animal burrows is critical. Burrows 

should be backfilled and animals removed as soon as 

possible.

Owners should inspect their dams in a regular and thorough manner.

Pond levels should be monitored and safety precautions 

such as spillways and freeboard should be factored into 

design.

The second consideration presents the most current and 

widespread dilemma facing the entire dam community. 

Many dam owners conduct inspections and typical maintenance as required, but preventive measures and wildlife 

mitigation actions may also be required. It would seem 

that vigilant dam owners would ensure the required actions were forthcoming; however, this is not always the case. 

According to the workshop (FEMA, 2001) and the state 

surveys (FEMA, 2003), and as echoed in the document The 

Cost of Rehabilitating Our Nation's Dams (ASDSO, 2003), 

owners of dams in need of repair are often not able to 

finance the required actions due largely to a lack of funding 

mechanisms at the state and federal levels; dams become 

neglected and deteriorate to the point of being hazardous. 

Currently, there are only a handful of states that provide 

financial assistance in the form of loans or grants to repair 

unsafe dams, as presented in Table 7-2.

•

•

•

Animal Burrows Contribute to $5 Million Dam 

Breach 

Wallula, Iowa

The Iowa Beef Processor’s (IBP) Waste Pond was 

constructed in 1971 to store wastewater from the 

IBP Plant. When full, the pond had a surface area of 

37 acres and a maximum storage capacity of 270 

acre-feet. The pond was located on a natural drainage 

course and was impounded behind a 15-foot-high, 

1000-foot-long earthen dam. State inspections in 

1981 and 1985 discovered that the embankment was 

riddled with animal burrows. It was recommended 

that the burrows be filled and the animals removed 

from the site. Repairs were not made quickly enough, 

and the rapid melting of record snow pack coupled 

with higher than normal pond levels filled the waste 

pond and overtopped a portion of the west end of 

the dam (the dam had no emergency spillway). High 

pond levels allowed water to exit through animal 

burrows that were normally above the pond elevation. Uncontrolled leakage and seepage through the 

animal borrows exiting on the downstream face likely 

resulted in erosion that backcut rapidly toward the upstream face, eventually breaching the dam.

The estimated cost of the failure was $5 million, 

which included the cost of the five locomotives that 

were derailed downstream, environmental cleanup, 

and repair to the rail line. The cost to construct a new 

facility was several million more dollars.
100 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

State Program Name and Type Eligibility Loan/Grant Amount

Arizona Dam Repair (loan or grant) State engineer determines dam to

be dangerous to life, non-emergency

Loan – Cost of project

Maryland Maryland Environmental Service (loan

and planning assistance)

Counties, utilities, and private

groups; must have established

service district for water supply,

resource reclamation, dredging or

stormwater

Massachusetts No name given (grants) Local communities for repair or

removal

75% of the project; local share

can be in-kind contributions

New Jersey Dam Restoration and Clean Water Trust

Fund (revolving loan fund; new grant

fund for municipally-owned dams)

Local units of governments; private

owners can be co-applicants

Loan – Cost of project

Grants – Up to 100%

New York Clean Water/Clean Air Bond Act

(grants)

Municipalities for dam safety

projects

75% of eligible project with 25%

local match; $300,000 cap per

project

Ohio Ohio Water Development Authority

(revolving loan fund)

Owner must be under mandate from

ODNR

Dam Safety Loan Program – Local

units of government, state, districts

Dam Safety Linked Deposit Program

– private owners/organizations

Cost of project

Pennsylvania Pennvest (revolving loan fund) Projects associated with wastewater,

water supply, or stormwater

Up to cost of project

Utah Utah Board of Water Resources (loans

or grants)

High hazard dam owners; mandated

repairs

80-95% grant for irrigation or water

supply dams; loans or grants for

other owners

Wisconsin DNR Municipal Dam Grant Program

(grants)

Local units of government and lake

districts

50-50 grants; $200,000

maximum

Table 7-2 Summary of State Dam Funding Programs 

Similarly, the federal government extends dam rehabilitation 

assistance through only a few programs. The combination 

of existing state and federal assistance does not approach 

the estimated $36.2 billion needed nationwide to support 

needed dam repair and rehabilitation related to wildlife 

damages and other structural integrity issues.
Chapter 7. Fiscal Considerations For Managing Animal Damage On Earthen Dams 101

Table 7-3. Summary of Potential Federal Programs for Dam Management

In conclusion, the dam community is composed of owners 

in need of education and economic understanding of the 

consequences associated with neglected dams, as well as 

those owners who are diligent in dam upkeep, but perhaps 

unable to fund the necessary repair and preventive actions. 

Even if federal, state, and local agencies can educate the 

reluctant dam owners such that they become vigilant in the 

upkeep of their dams, our nation's dams will likely continue 

to degrade without adequate funding to implement the 

sometimes perpetual animal damage repair and management needed.

Agency Program Description

Natural Resources

Conservation Service,

Department of Agriculture

10.916 Watershed

Rehabilitation Program

Provides grants to rehabilitate dams originally built with assistance from

USDA Watershed Programs. Rehabilitation must extend the life of the dam

and meet applicable performance and safety requirements. Priority is given to

high hazard dams.

Natural Resources

Conservation Service,

Department of Agriculture

10.904 Watershed

Protection and Flood

Prevention

Provides grants and technical assistance to carry out watershed improvement

projects that protect, develop, and utilize the land and water resources in

small watersheds.

Bureau of Indian Affairs,

Department of the Interior

15.065 Safety of Dams

on Indian Lands

Provides direct payments to federally recognized Indian tribal governments

and Native American organization to improve the structural integrity of dams

on Indian lands.

Federal Emergency

Management Agency,

Department of Homeland

Security

97.047 Pre-Disaster

Mitigation (PDM)

Provides grants to states and communities for cost-effective hazard

mitigation activities that are part of a comprehensive mitigation program, and

that reduce injuries, loss of life, and damage and destruction of property.

Dam repair and rehabilitation projects may be eligible for PDM funding if:

Federal Emergency

Management Agency,

Department of Homeland

Security

P.L. 107-310 National

Dam Safety and Security

Act of 2002

Funds are granted each year to state dam safety programs.

Federal Insurance and

Mitigation Administration,

Federal Emergency

Management Agency

83.550 National Dam

Safety Program (Dam

Safety State Assistance

Program)

Funds are distributed each year (in the form of project grants) to state dam

safety programs.

• The project has a high benefit-cost ratio; 

• There is a high risk of dam failure or dam failure would result in 

significant damages; and 

• The project is consistent with State funding priorities. 
102 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

Association of State Dam Safety Officials. 2001. ASDSO West 

Region Technical Seminar. Plant and Animal Penetrations of Earthen Dams. Dr. B. Dan Marks, P.E.; Dr. Bruce 

Tschantz, P.E., and Mr. David K. Woodward, M.S., editors.

Association of State Dam Safety Officials. 2002. A Technical Manual on the Effects of Tree and Woody Vegetation 

Root Penetrations on the Safety of Earthen Dams.

Association of State Dam Safety Officials. 2003. The Cost 

of Rehabilitating our Nation’s Dams: A Methodology, 

Estimate & Proposed Funding Mechanisms.. 

Barnes, Thomas G. 1991. Managing Beaver Problems in 

Kentucky. University of Kentucky College of Agriculture. 

http://www.ca.uky.edu/agc/pubs/for/for50/for50.

htm. Site accessed December 8, 2003.

Benyus, Janine M. 1989. The Field Guide to Wildlife Habitats of the Eastern United States. Simon & Schuster Inc.: 

New York, New York.

Colorado State University Cooperative Extension. 2003. 

Managing Pocket Gophers. www.ext.colostate.edu/

pubs/natres/06515.html. Site accessed December 3, 

2003.

Connecticut Department of Environmental Protection. 1999. 

Muskrat. http://dep.state.ct.us/burnatr/wildlife/factshts/muskrat.htm Site accessed December 12, 2003. 

Enchanted Forest Nature Sanctuary. 2003. Gopher Tortoises. 

http://nbbd.com/godo/ef/gtortoise/ Site accessed 

October 31, 2003. 

Federal Emergency Management Agency. 2000. Report on 

Specialty Workshop #1. Plant and Animal Impacts on 

Earthen Dams. Prepared by the Association of State Dam 

Safety Officials; Lexington, Kentucky.

Federal Emergency Management Agency. 2003. Dam Owner’s Guide to Plant Intrusion of Earthen Dams. Prepared 

by URS Group, Inc.

8.0 References
Chapter 8. References 103

Gopher Tortoise Council. 2001. The Gopher Tortoise: A Species in Decline. http://www. gophertortoisecouncil.

org/tortoise.htm. Site visited October 31, 2003; and 

Novermber 4, 2004.

Indiana Department of Natural Resources. 2003. Dam 

Safety: Rodent Control. Fact Sheet 03-14.

Indiana Department of Natural Resources. 2003. Division of 

Water. Indiana Dam Safety Inspection Manual.

Michigan State University Extension. 1998. Aquatic Pest 

Management: A Training Manual for Commercial Pesticide Applicators (Category 5). http://www.msue.msu.

edu/msue/imp/modet/morefile/e-2437.pdf. Site accessed December 12, 2003. 

New York State Department of Environmental Conservation 

(DEC). 2002. Handout #5 Modifying Sites to Discourage Beaver Occupation. http://www.dec.state.ny.us/

website/dfwmr/wildlife/beaver/handout5.htm. Site 

accessed December 8, 2003. 

Niering, William A. 1985. Wetlands. Chanticleer Press, Inc. 

New York.

North Carolina State University. 1994. Beavers. http://www.

ces.nscu.edu/nreos/wild/wildlife/wdc/beavers.html. 

Site accessed December 8, 2003. 

__2003. Wildlife. http://h2osparc.wq.ncsu.edu/wetland/

aqlife/wildlife.html. Site accessed October 31, 2003. 

Ohio Department of Natural Resources (DNR). 1999. Dam 

Safety: Rodent Control. http://www.dnr.state.oh.us/

water/pubs/fs_div/fctsht27.htm. Site accessed November 11, 2003. 

Peckarsky, Barbara L., Pierre R. Fraissinet, Marjory A. Penton, 

and Don J. Conklin Jr. 1990. Freshwater Macroinvertebrates of Northeastern North America. Cornell University Press: Ithaca, New York. 

Pehling, Dave. 2003. Principles of Vertebrate Pest Management. http://snohomish.wsu.edu/vertchap.htm. Site 

accessed December 10, 2003.

Pennsylvania Department of Environmental Protection 

(DEP). 1995. Liability and Responsibility of Dam Owners. 3200-FS-DEP-1954. http://www.dep. state.pa.us/

dep/deputate/watermgt/WE/FactSheets/Dam/fs1954.

htm. Site accessed December 8, 2003. 

Porter, Mike. 2003. Beaver Damage Preventable With Appropriate Techniques. Noble Foundation. http://www.

noble.org/Ag/Wildlife/BeaverDamagePreventable/ Site 

accessed December 8, 2003. 

Salisbury, David. 1998. $20 Billion Needed to Ensure Safety 

of Nation’s Dams, Engineer Estimates. Stanford Online Report. http://news-service.stanford.edu/news/

march11/damsafety.html. Site accessed November 11, 

2003. 

Smith, Diana. 2003. University of Nebraska. Personal 

Communication with E. Zamensky. URS Corporation. 

October 21. 

__2004. University of Nebraska. Personal Communication 

with E. Zamensky. URS Corporation. Novermber 22.

South Carolina Department of Natural Resources. 2003. 

The Muskrat in South Carolina: Biology, Management 

& Control. www.dnr.state.sc.us/wild/img/muskrat.pdf. 

Site accessed November 21, 2003. 

Texas Wildlife Management Damage Service. 1998. Controlling Badger Damage. Publication L-1923. 

U.S. Department of Agriculture. 1991. Prevention and Control of Animal Damage to Hydraulic Structures. 

U.S. Fish and Wildlife Service. 2002a. ESA Basics. http://endangered.fws.gov/pubs/esa%20basics.pdf. Site accessed 

November 3, 2003.

__2002b. Migratory Bird Permits. http://birds.fws.gov/Permits-Fact-Sheet.pdf. Site accessed November 3, 2003.

U.S. Forest Service. 1994. Animal Damage Management 

Handbook. Pacific Northwest Research Station.

University of Arizona. 1997. Ant Information. http://insected.arizona.edu/antinfo.htm. Site accessed November 

25, 2003.
104 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

University of Florida Cooperative Extension Service. 2002. 

Ants. http://edis.ifas.ufl.edu/BODY_IG080. Site accessed November 25, 2003. 

University of Georgia Cooperative Extension Service. 1993. 

Controlling Fire Ants in Urban Areas. Bulletin 1068. 

http://www.ces.uga.edu/pubcd/b1068-w.html. Site 

accessed December 4, 2003.

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in Urban Areas. Bulletin 1191. http://www.ces.uga. 

edu/pubcd/B1191.htm. Site accessed December 4, 

2203.

University of Michigan Museum of Zoology. 2002. Branta 

Canadensis. http://animaldiversity.ummz.umich.

edu/accounts/branta/b._canadensis$narrative.html Site 

accessed November 25, 2003. 

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http://muextension.missouri.edu/explore/miscpubs/

mx0136.htm. Site accessed June 2, 2003. 

University of Nebraska. 1994a. Prevention and Control of 

Wildlife Damage.

__1994b. Animal Damage Management Handbook. General 

Technical Report PNW-GTR-332. 

__2003. Fact Sheet: Managing Canada Goose Damage. 

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12, 2003. 

Virginia Cooperative Extension. 2000. Managing Wildlife Damage: Beavers (Castor Canadensis). Publication 

Number 420-202. http://www.ext.vt.edu/pubs/wildlife/420-202/420-202.html. Site accessed December 8, 

2003. 

Virginia Dam Safety Program. 2003. www.dcr.state.va.us/

sw/damrdnts.htm. Site accessed June 2, 2003.

Virginia Tech. 2001a. The Control of Burrowing Crayfish in 

Ponds. Publication Number 420-253. http://www.ext.

vt.edu/pubs/fisheries/420-253/420-253.html. Site accessed November 17, 2003.

__2001b. Managing Wildlife Damage: Canada Goose (Branta 

canadensis). Publication Number 420-203. http://

www.ext.vt.edu/pubs/wildlife/420-203/420-203.

html. Site accessed November 25, 2003. 

Washington State Department of Ecology. 2003. Iowa Beef 

Processors Waste Pond. http://www.ecy.wa.gov/programs/wr/dams/iowa.html. Site accessed November 

13, 2003.

Water Webster. 2003. America’s Crumbling Infrastructure: 

$36 billion needed to fix nation’s dams; $10.1 billion 

for ‘most critical’ structures. http://www.waterwebster.

com/Assn.ofStateDamSafetyOfficialsNov.102003.htm. 

Site accessed December 8, 2003. 

Wilson, Judy M. 2001. Beavers in Connecticut: Their Natural 

History and Management. Connecticut Department of 

Environmental Protection. 

Witmer, Gary W., Rodney D. Sayler, and Michael J. Pipas. 

1995. Repellant Trial to Reduce Reforestation Damage 

by Pocket Gophers, Deer, and Elk. In: Proceedings of the 

Second DWRC Special Symposium: pp. 321-332.
Appendix A. State Wildlife Agency Contacts 105

Alabama Department of Conservation and Natural Resources

Division of Wildlife and Freshwater Fisheries

64 N. Union Street

Montgomery, Alabama 36130

(334) 242-3469

Alaska Department of Fish and Game

PO Box 25526

Juneau, Alaska 99802-5526

(907) 465-4100

Arizona Game and Fish Department

2221 W. Greenway Road

Phoenix, Arizona 85023-4399

(602) 942-3000

Arkansas Game and Fish Commission

Natural Resources Drive

Little Rock, Arkansas 72205

(501) 223-6359

California Department of Fish and Game

1416 Ninth Street

Sacramento, California 95814

(916) 445-0411

Colorado Department of Natural Resources

Division of Wildlife

6060 Broadway 

Denver, Colorado 80216

(303) 297-1192 

Connecticut Department of Environmental Protection

Bureau of Natural Resources, Wildlife Division

79 Elm Street

Hartford, Connecticut 06106-5127

(860) 424-3011

Delaware Department of Natural Resources and 

Environmental Control

Division of Fish and Wildlife

89 Kings Highway

Dover, Delaware 19901

(302) 739-5297

Florida Fish and Wildlife Conservation Commission

620 South Meridian Street

Tallahassee, Florida 32399-1600

(850) 921-5990 

Appendix A

State Wildlife Agency Contacts
106 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

Georgia Department of Natural Resources

Wildlife Resources Division

2070 U.S. Highway 278, S.E.

Social Circle, Georgia 30025

(770) 918-6400

Hawaii Department of Land and Natural Resources

Division of Forestry and Wildlife

1151 Punchbowl Street, Room 325

Honolulu, Hawaii 96813

(808) 587-0166

Idaho Department of Fish and Game

600 S. Walnut, PO Box 25

Boise, Idaho 83707

(208) 334-3700

Illinois Department of Natural Resources

1 Natural Resources Way

Springfield, Illinois 62702-1271

(217) 782-6302

Indiana Department of Natural Resources

Division of Fish and Wildlife

402 W. Washington Street, Room W273 

Indianapolis, Indiana 46204

(317) 232-4080

Iowa Department of Natural Resources

Wildlife Bureau

Henry A. Wallace Building 

502 E. 9th Street

Des Moines, Iowa 50319-0034 

(515) 281-5918 

Kansas Department of Wildlife and Parks

14639 W. 95th

Lenexa, Kansas 66215 

(913) 894-9113

Kentucky Department of Fish and Wildlife

1 Game Farm Road

Frankfort, Kentucky 40601

(800) 858-1549

Louisiana Department of Wildlife and Fisheries

2000 Quail Drive

Baton Rouge, Louisiana.70808

(225) 763-3557

Maine Department of Inland Fisheries and Wildlife

284 State Street

41 State House Station

Augusta, Maine 04333-0041

(207) 287-8000

Maryland Department of Natural Resources

Wildlife and Heritage Service

Tawes State Office Building, E-1 

580 Taylor Avenue 

Annapolis, Maryland 21401

(410) 260-8540 

Massachusetts Department of Fisheries, Wildlife and 

Environmental Law Enforcement

Division of Fisheries & Wildlife

251 Causeway Street, Suite 400

Boston, Massachusetts 02114-2152

(617) 626-1590

Michigan Department of Natural Resources

Wildlife Division

Mason Building, Fourth Floor

PO Box 30444

Lansing, Michigan 48909-7944

(517) 373-1263

Minnesota Department of Natural Resources

500 Lafayette Road

St. Paul, Minnesota 55155-4040

(651) 296-6157

Mississippi Department of Wildlife, Fisheries and Parks

1505 Eastover Drive

Jackson, Mississippi 39211-6374

(601) 432-2400

Missouri Department of Conservation

2901 W. Truman Boulevard

Jefferson City, Missouri 65109

(573) 751-4115

Montana Fish, Wildlife & Parks

1420 East Sixth Avenue

Helena, Montana 59620-0701

(406) 444-2535
Appendix A. State Wildlife Agency Contacts 107

Nebraska Game and Parks Commission

2200 North 33rd Street

Lincoln, Nebraska 68503

(402) 471-0641

Nevada Department of Wildlife

1100 Valley Road

Reno, Nevada 89512

(775) 688-1500

New Hampshire Fish and Game Department

Wildlife Division

11 Hazen Drive

Concord, New Hampshire 03301

(603) 271-2461

New Jersey Department of Environmental Protection

Division of Fish and Wildlife

PO Box 400

Trenton, New Jersey 08625-0400

(609) 292-2965

New Mexico Department of Game and Fish

PO Box 25112

Santa Fe, New Mexico 87507

(800) 862-9310

New York State Department of Environmental Conservation

Division of Fish, Wildlife and Marine Resources

625 Broadway

Albany, New York 12233-4750

(518) 402-8919

North Carolina Wildlife Resources Commission

Archdale Building

512 N. Salisbury Street

Raleigh, North Carolina 27604-1188

(919) 733-7191

North Dakota Game and Fish Department

100 N. Bismarck Expressway 

Bismarck, North Dakota 58501-5095

(701) 328-6300

Ohio Department of Natural Resources

Division of Wildlife

1840 Belcher Drive 

Columbus, Ohio 43224-1300

(800) 945-3543

Oklahoma Department of Wildlife Conservation

1801 N. Lincoln

Oklahoma City, Oklahoma 73105

(405) 521-3851

Oregon Department of Fish and Wildlife

3406 Cherry Avenue N.E.

Salem, Oregon 97303-4924

(503) 947-6000

Pennsylvania Game Commission

2001 Elmerton Avenue

Harrisburg, Pennsylvania 17110-9797

(717) 787-4250

Rhode Island Department of Environmental Management

Division of Fish and Wildlife

4808 Tower Hill Road

Wakefield, Rhode Island 02879

(401) 789-3094

South Carolina Department of Natural Resources

Wildlife and Freshwater Fisheries Division

PO Box 167

Columbia, South Carolina 29202

(803) 734-3886

South Dakota Department of Game, Fish, and Parks

Wildlife Division

523 East Capitol Avenue

Pierre, South Dakota 57501-3182

(605) 773-3381

Tennessee Wildlife Resources Agency

Wildlife Division

Ellington Agricultural Center

PO Box 40747

Nashville, Tennessee 37204

(615) 781-6610

Texas Parks and Wildlife Department

4200 Smith School Road

Austin, Texas 78744

(800) 792-1112 

Utah Department of Natural Resources

Division of Wildlife Resources

1594 W. North Temple

Salt Lake City, Utah 84114

(801) 538-4700
108 Dam Owner’s Manual to Animal Intrusion of Earthen Dams

Vermont Agency of Natural Resources

Fish and Wildlife Department

103 South Main Street 

Waterbury, Vermont 05671-0501

(802) 241-3700

Virginia Department of Game and Inland Fisheries

4010 West Broad Street

Richmond, Virginia 23230

(804) 367-1000 

Washington Department of Fish and Wildlife

Natural Resources Building 

1111 Washington Street, SE

Olympia, Washington 98501

(360) 902-2200

West Virginia Division of Natural Resources

Wildlife Resources

State Capitol Building 3, Room 812

Charleston, West Virginia 25305

(304) 558-2771

Wisconsin Department of Natural Resources

101 South Webster Street

Madison, Wisconsin 53703

(608) 266-2621

Wyoming Game and Fish Department

5400 Bishop Boulevard

Cheyenne, Wyoming 82006-0001

(307) 777-4600
Appendix B. Association of State Dam Safety Officials Contact Information 109

Association of State Dam Safety Officials 

450 Old Vine Street, 2nd Floor 

Lexington, KY 40507-1544 

Phone: 859-257-5140 

Fax: 859-323-1958 

E-Mail: info@damsafety.org 

Web: www.damsafety.org

Lori Spragens, Executive Director lspragens@damsafety.org 

Susan Sorrell, Meetings & Membership Director 

sasorrell@damsafety.org 

Sarah Mayfield, Information Specialist smayfield@damsafety.

org 

Maureen Hogle, Administrative Database Specialist 

mhogle@damsafety.org

Appendix B

Association of State Dam Safety 

Officials Contact Information 

For information on obtaining a print, CD, or online 

version of this publication or the technical manual go 

to www.fema.gov/fima/damsafe