Hydraulic Laboratory Report HL-2022-02 

Glen Canyon Dam Fish Escapement 

Options 

Colorado River Storage Project 

Upper Colorado Basin Region 

U.S. Department of the Interior September 2022 
 

 

 

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1. REPORT DATE (DD-MM-YYYY) 

09/01/2022 

2. REPORT TYPE 

Technical 

3. DATES COVERED (From - To) 

2022 

4. TITLE AND SUBTITLE 

Glen Canyon Dam Fish Escapement Options 

5a. CONTRACT NUMBER 

5b. GRANT NUMBER 

5c. PROGRAM ELEMENT NUMBER 

6. AUTHOR(S) 

Svoboda, Connie D. 

5d. PROJECT NUMBER 

5e. TASK NUMBER 

5f. WORK UNIT NUMBER 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 

Bureau of Reclamation, Technical Service Center 

Hydraulic Investigations and Laboratory Services 

8. PERFORMING ORGANIZATION REPORT 

NUMBER 

HL-2022-02 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 

Bureau of Reclamation, Upper Colorado Region 

10. SPONSOR/MONITOR'S ACRONYM(S) 

11. SPONSOR/MONITOR'S REPORT 

NUMBER(S) 

12. DISTRIBUTION/AVAILABILITY STATEMENT 

13. SUPPLEMENTARY NOTES 

14. ABSTRACT

As water levels in Lake Powell on the Colorado River in Utah and Arizona are declining to historically low levels, the epilimnion where some 

non-native fish reside approaches the penstock intake elevations at Glen Canyon Dam. Non-native fish entrained through the penstocks 

threaten to compete with and/or predate the downstream native fish community, including threatened and endangered species. This study 

explores fish exclusion devices that may limit fish escapement from reservoirs through physical exclusion, behavioral exclusion, or by 

reducing downstream survival. Relevant example projects were identified, and alternatives were assessed in the context of preventing fish 

passage through Glen Canyon Dam. Applicability was based on scalability, effectiveness, operational impact and loss of power production, 

inspection and maintenance requirements, and recreational impact. There is no clear alternative that can fully eliminate non-native fish 

escapement from Glen Canyon Dam. Based on the review of applicable projects, a forebay barrier net or multi-stimulus barrier may be the 

most likely alternative to limit impacts to power production, operations, and recreation while maintaining a reasonable level of entrainment 

protection. Deeper water withdrawal through the river outlet works or installation of an energy dissipating valve on the penstock pipe will 

also likely limit passage of non-native fish, but considerable impacts to power production are expected. Preferred alternatives should be 

evaluated in greater detail to identify possible installation layouts and design features, anchoring strategies, anticipated efficacy, impacts to 

power production, implementation timeframe, and initial and ongoing costs. 

15. SUBJECT TERMS 

Fish passage, fish entrainment, fish escapement, fish barriers, behavioral barriers, non-native fish 

16. SECURITY CLASSIFICATION OF: 17. LIMITATION 

OF ABSTRACT 

18. NUMBER 

OF PAGES 

35

19a. NAME OF RESPONSIBLE PERSON 

Connie D. Svoboda 

a. REPORT b. ABSTRACT a. THIS PAGE 19b. TELEPHONE NUMBER (Include area code) 

303-445-2152

Standard Form 298 (Rev. 8/98) 

Prescribed by ANSI Std. Z39.18 
Hydraulic Laboratory Report HL-2022-02 

Glen Canyon Dam Fish Escapement 

Options 

Colorado River Storage Project 

Upper Colorado Basin Region 

prepared by 

CONNIE SVOBODA Digitally signed by CONNIE SVOBODA 

Date: 2022.10.11 14:27:33 -06'00'

Connie D. Svoboda, P.E. 

Manager, Hydraulic Investigations and Laboratory Services, 86-68560 

reviewed by 

Digitally signed by BRYAN HEINER 

Date: 2022.10.11 18:34:41 -06'00'

Peer Review: Bryan Heiner, P.E. 

Hydraulic Engineer, Hydraulic Investigations and Laboratory Services, 86-68560 

MICHAEL HORN Digitally signed by MICHAEL HORN 

Date: 2022.10.12 06:44:39 -06'00'

Peer Review: Mike Horn 

Manager, Fisheries and Wildlife Resources, 86-68290 

U.S. Department of the Interior 

Bureau of Reclamation 

Technical Service Center 

Hydraulic Investigations and Laboratory Services 

Denver, Colorado September 2022 
 

 

 

Mission Statements 

The mission of the Department of the Interior is to protect and 

manage the Nation’s natural resources and cultural heritage; provide 

scientific and other information about those resources; and honor its 

trust responsibilities or special commitments to American Indians, 

Alaska Natives, and affiliated island communities. 

The mission of the Bureau of Reclamation is to manage, develop, and 

protect water and related resources in an environmentally and 

economically sound manner in the interest of the American public. 

Hydraulic Laboratory Reports 

The Hydraulic Laboratory Report series is produced by the Bureau of Reclamation’s Hydraulic 

Investigations and Laboratory Services Group (Mail Code 86-68560), PO Box 25007, Denver, Colorado 

80225-0007. This report was made available online at https://www.usbr.gov/tsc/ 

Disclaimer 

The information provided in this report is believed to be appropriate and accurate for the specific purposes 

described herein, but users bear all responsibility for exercising sound engineering judgment in its 

application, especially to situations different from those studied. References to commercial products do not 

imply endorsement by the Bureau of Reclamation and may not be used for advertising or promotional 

purposes. 

Cover Photo: Aerial photograph of Glen Canyon Dam. 

Funding was provided by the Bureau of Reclamation’s Upper Colorado Basin Region. 
Contents 

EXECUTIVE SUMMARY..............................................................................................................................1 

INTRODUCTION...........................................................................................................................................2 

APPROACH ......................................................................................................................................................3 

CONSIDERATIONS ......................................................................................................................................3 

REVIEW OF OPTIONS.................................................................................................................................4 

In-Reservoir Barrier Options ....................................................................................................................4 

Physical Barrier Screens.......................................................................................................................4 

Barrier Nets...........................................................................................................................................6 

Air Bubble Curtains and Underwater Acoustic Barriers................................................................8 

Multi-Stimulus Barriers......................................................................................................................10 

Carbon Dioxide Barrier.....................................................................................................................11 

Floating Barriers .................................................................................................................................12 

Electrical Barriers ...............................................................................................................................13 

Other In-Reservoir Barriers..............................................................................................................15 

At Dam Options .......................................................................................................................................15 

Deeper Water Withdrawal ................................................................................................................15 

Turbine Mortality ...............................................................................................................................16 

Energy Dissipating Valve..................................................................................................................17 

Other At Dam Options.....................................................................................................................17 

Downstream Removal..............................................................................................................................18 

Manual Collection and Removal......................................................................................................18 

Other Downstream Options ............................................................................................................18 

DISCUSSION..................................................................................................................................................19 

REFERENCES................................................................................................................................................25 

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Executive Summary 

Water levels in Lake Powell on the Colorado River in Utah and Arizona are declining to historically 

low levels due to the extended drought in the western United States. With a reduced water surface 

elevation, the epilimnion where some non-native fish reside approaches the penstock intake 

elevations at Glen Canyon Dam and the risk of fish entrainment increases. Non-native fish species 

threaten to compete with and/or predate the downstream native fish community, including 

threatened and endangered species such as Humpback Chub Gila cypha and Razorback Suckers 

Xyrauchen texanus. 

This study explores fish exclusion devices that may limit fish escapement from reservoirs through 

physical exclusion, behavioral exclusion, or by reducing downstream survival. Relevant example 

projects were identified where fish escapement solutions have been installed or were considered for 

installation. Alternatives were assessed in the context of preventing fish passage through Glen 

Canyon Dam. Applicability was based on scalability to large lateral and vertical dimensions and large 

capacity withdrawal, effectiveness in excluding non-native fish populations, operational impact or 

loss of power production, inspection and maintenance requirements, and recreational impact. 

In-reservoir options included physical barrier screens, barrier nets, air bubble curtains, underwater 

acoustic barriers, multi-stimulus barriers, carbon dioxide barriers, floating barriers, and electric 

barriers. At dam options included deeper water withdrawal, turbine mortality, and energy dissipating 

valves. Downstream removal options such as manual collection and removal through collection and 

sorting facilities and boat-based electrofishing and netting were also explored. 

Preventing downstream movement of non-native fish from Lake Powell to the Colorado River 

downstream of Glen Canyon Dam is a difficult problem without a definitive solution. There is no 

clear alternative that can fully eliminate fish escapement. Based on the review of applicable projects, 

a forebay barrier net or multi-stimulus barrier may be the most likely alternative to limit impacts to 

power production, operations, and recreation while maintaining a reasonable level of entrainment 

protection. Deeper water withdrawal through the river outlet works will likely reduce fish 

entrainment, but water releases through the outlet works bypass the turbines and power production 

is currently not possible. Another option is installation of an energy dissipating valve on the 

penstock pipe to limit fish survival, but this device will impact power production by increasing 

headloss in the penstock pipe. Preferred alternatives should be evaluated in greater detail to identify 

possible installation layouts and design features, anchoring strategies, anticipated efficacy, impacts to 

power production, implementation timeframe, and initial and ongoing costs. 

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Introduction 

Water levels in Lake Powell on the Colorado River in Utah and Arizona are declining to historically 

low levels due to the extended drought in the western United States. Glen Canyon Dam is a 

concrete arch structure with a structural height of 710 ft, a hydraulic height of 583 ft, and a crest 

length of 1,560 ft. Eight 15-ft-diameter steel penstocks are embedded in the dam for power 

production. The minimum water surface elevation for power operation is 3490 ft. The river outlet 

works, located near the left abutment, consist of two intake structures with trash racks, four 96-inchdiameter steel pipes, ring-follower guard gates, and hollow-jet valves for flow regulation. The 

centerline of each river outlet intake is 96 ft below the centerline of the penstock intakes. 

With a reduced water surface elevation, the epilimnion where some non-native fish reside currently 

approaches the penstock intake elevations at Glen Canyon Dam and the risk of fish entrainment 

increases. The 2016 Long Term Experimental and Monitoring Plan Biological Opinion (U.S. Fish 

and Wildlife Service 2016) directed the Bureau of Reclamation (Reclamation) to pursue means of 

preventing the passage of deleterious invasive non-native fish through Glen Canyon Dam. 

Above Glen Canyon Dam, the fish assemblage is mostly non-native sport fish (e.g., Smallmouth 

Bass Micropterus dolomieu, Striped Bass Morone saxatilis, Walleye Sander vitreus, Green Sunfish Lepomis 

cyanellus, Black Crappie Pomoxis nigromaculatus, Bluegill Sunfish Lepomis macrochirus, Channel Catfish 

Ictalurus punctatus) and below Glen Canyon Dam in Glen, Marble, and Grand Canyons, the fish 

assemblage consists of mostly native fish including the threatened Humpback Chub Gila cypha and 

endangered species Razorback Sucker Xyrauchen texanus. There is a Rainbow Trout Oncorhynchus 

mykiss fishery immediately below the dam that extends through Glen Canyon. A 2007-2009 

hydroacoustic survey demonstrated there are non-native sport fish in the reservoir forebay that 

could become entrained in the penstocks when water is withdrawn from the epilimnion. Results of 

the hydroacoustic survey show that most sampled fish were found in the top 14 m (45.9 ft) of the 

water column for both light and dark periods with the first 4 m (13.1 ft) of water having the highest 

densities of fish (Bureau of Reclamation 2012). Forebay fish densities were highest during the 

summer months. 

Downstream in Lees Ferry, Striped Bass and other non-native fish species have been detected 

during routine monitoring by the Grand Canyon Monitoring and Research Center (GCMRC) and 

Arizona Game and Fish Department (AZGFD), but water temperatures are now warm enough that 

there is risk of establishment. In July 2022, juvenile Smallmouth Bass were detected in the Colorado 

River below Glen Canyon Dam. These non-native fishes threaten to compete with and/or predate 

the downstream native fish community. The financial cost to Reclamation may be very high if longterm non-native fish eradication efforts are required. 

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Approach 

The goal of this study is to explore fish exclusion devices and methodologies to restrict non-native 

fish in the reservoir from passing through Glen Canyon Dam powerplant and into the downstream 

river. This study includes a review of devices that may limit fish escapement from reservoirs through 

physical exclusion, behavioral exclusion, or by reducing survival. Literature was reviewed and subject 

matter experts were contacted in all of Reclamation’s regions, along with other federal and state 

entities, to obtain best professional input on fish escapement strategies. Results from the 2020 Fish 

Protection Prize competition conducted by Reclamation and the Department of Energy Water 

Power Technologies Office and the 2019 Improving Fish Exclusion from Water Diversions and 

Intakes prize competition conducted by Reclamation were reviewed. Relevant example projects were 

identified where fish escapement solutions have been installed or were considered for installation by 

Reclamation or other entities. 

Alternatives were assessed in the context of preventing fish passage through Glen Canyon Dam. 

Applicability was based on: 

• Scalability to large lateral and vertical dimensions and large capacity withdrawal 

• Effectiveness in excluding non-native fish populations, particularly mid-size fish 

• No operational impact or loss of power production 

• Inspection and maintenance requirements (including impacts by invasive mussels) 

• Recreational impact 

Considerations 

Due to the urgency of the fish escapement problem, viable technologies should be field tested and 

commercially available rather than theoretical concepts that require significant development. 

Identified technologies should address longer-term solutions rather than stop-gap measures. The 

focus of the evaluation is on mid-size fish due to the possibility of this size class surviving passage 

through Francis turbines. It is likely that larger adult fish will be susceptible to turbine blade strikes 

and larval fish will be most susceptible to pressure change and shear stress. In addition, Lewis et al. 

(2022) report that small-bodied individuals tended to escape from reservoirs at higher rates than 

larger fish. 

Inspection and maintenance requirements will be elevated due to the presence of invasive quagga 

mussels Dreissena bugensis in Lake Powell. Quagga mussel issues were first detected at the Glen 

Canyon powerplant in 2013. Mussels are considered a moderate problem at the powerplant. The 

most impacted components at the powerplant are Bailey valves, transformer cooling system, fixed 

wheel gates, and service station air compressors (Pucherelli et al. 2021). A 2019 study found rapid 

progression of mussel settlement on the penstock intake trashracks since a previous survey in 2017. 

Complete occlusion is not likely due to the large size of the trashrack openings, but extensive fouling 

has the potential to increase velocities and increase head loss. 

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Infrastructure installed at the dam face or in the reservoir forebay will be susceptible to biofouling 

by mussels. The highest densities of mussels are found near existing infrastructure and canyon walls. 

Settlement of mussels on installed infrastructure may result in occlusion of components that result 

in the device not working properly (e.g., clogging of air bubble lines) or adding weight to a system 

that exceeds design specifications or impedes performance. Application of commercially available 

silicone foul release coatings may limit mussel attachment on fish barriers installed in Lake Powell, 

although abrasion and gouge resistance needs to be assessed (Skaja 2012). 

Colonial hydroid (Cordylophora caspia, Pallas, 1771) was found on settlement plates in Lake Powell in 

2015. Colonial hydroid colonies have significant biofouling potential at hydropower facilities, 

including increasing maintenance and causing system failure (Pucherelli et al. 2016), and may be a 

biofouling concern for newly installed fish barrier infrastructure. 

Local velocity is a factor in the design and effectiveness of fish exclusion technologies in the 

reservoir forebay. From a report on penstock withdrawal characteristics, near-field velocity 

measurements adjacent to the trashrack bars at the penstock centerline elevation for Unit 7 were 

1.64 ft/s during a release of 3,600 ft3/s (Vermeyen 2011). Velocity magnitudes decline to less than 

0.4 ft/s at a distance of 20 ft from the operating intake at 3,600 ft

3

/s. Far-field velocity 

measurements approximately 420 ft upstream of the dam face were less than 0.37 ft/s over a range 

of release flows (Vermeyen 2011). 

Installation of a barrier components in the reservoir forebay may create infrastructure safety 

concerns. If part of a barrier system dislodges, it could block spillways or outlets or become 

entrained in penstocks. A Risk Analysis to identify potential impacts to dam safety may be required. 

Review of Options 

In-Reservoir Barrier Options 

Physical Barrier Screens 

Description 

Physical barrier screens prevent the movement of fish into a diversion using a porous structure that 

allows water to flow through it while preventing objects larger than the opening size from moving 

through. There are many types of screens including vertical and horizontal flat plate screens, inclined 

screens, cylindrical and conical screens, Coanda screens, closed conduit screens (e.g., Eicher, 

Modular Inclined Screens (MIS)). Vertical wells and infiltration galleries (e.g., Ranney collector wells) 

can be used to withdraw water below the river bed. Rotating screens such as vertical or inclined 

traveling screens and cylindrical drum screens rotate to prevent debris from clogging the screen. 

Screens must have enough surface area to maintain low velocities through the screen to prevent fish 

from impinging on the screen face. Therefore, fish screens at large diversions or intakes can be very 

long. 

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The screen material is typically metal (e.g., woven wire, perforated plate, and profile bar) or 

engineered polymers. Screens are cleaned with automated traveling brushes, air burst, water jets, or 

manually raking the screen. Flow baffles or porosity boards (vertical louvers or perforated plate) 

designed to distribute diverted flow uniformly over the screen area can be located either behind the 

screen (flat screen panels) or inside the screen (cylindrical screen units). Recent research by a winner 

of the Fish Protection Prize was conducted to determine if a biometric-informed screen shape holds 

advantages for exclusion of larval fish and eggs (Benjamin Mater and Charles Coutant; 

https://americanmadechallenges.org/challenges/fishprotection/index.html). 

Related Examples 

The Interlake Tunnel Project is a proposed gravity water conveyance tunnel approximately 11,000 

feet long connecting Nacimiento and San Antonio reservoirs in San Luis Obispo and Monterey 

Counties, respectively. A screened intake structure would be constructed to prevent White Bass M. 

chrysops from moving from Lake Nacimiento to San Antonio Reservoir. The screening system would 

be comprised of four cylindrical screen assemblies at a 1.75-mm screen opening. The proposed 

location of the intake structure would likely preclude the presence of eggs and larvae. A debris 

management system would require a debris boom across the intake structure, a trashrack with trash 

rake within the intake approach channel, and cylindrical screens with external and internal brushes. 

At Willow Springs Lake in eastern Arizona, the Arizona Game and Fish Department is considering a 

fixed fish screen to prevent Smallmouth Bass and Green Sunfish escapement into Chevelon Canyon 

where several species of native fish reside, including listed Little Colorado Spinedace Lepidomeda 

vittata. Installation of a fish screen with 1/8-inch diameter holes is proposed to prevent downstream 

passage of nearly all fish except for small fry. The 40-ft-wide by 4-ft-tall fish screen would be 

installed downstream of the control structure in the spillway with operation up to a 25-year flow 

event. Annual mechanical removal efforts via boat electrofishing are currently conducted. 

The Colorado Division of Parks and Wildlife operates a fish screen in Rifle Creek (Garfield County, 

Colorado) to prevent non-native fish in Rifle Gap Reservoir from entering the downstream 

Colorado River via Rifle Creek. The project aims to assist in recovery of listed species such as 

Humpback Chub, Razorback Sucker, Bonytail Chub Gila elegans, Colorado Pikeminnow Ptychocheilus 

lucius. The screening structure consists of a concrete structure with two 50-ft-long by 5-ft-wide 

Coanda screens. The two screens are constructed parallel to each other to minimize the overall 

structure size while maintaining a maximum flow capacity of 200 ft3

/s. Water is retained by a 

concrete barrier and pools up until it overtops the side of the concrete channel and flows down the 

angled screens. Most water passes through the screen with a mesh size of 3/32-inch opening. Larger 

objects such as fish and debris are collected in concrete troughs. Fish are sorted manually and 

selectively relocated. Debris must be removed manually from the screen by staff with a long-handled 

brush. 

Fish protection alternatives were considered in 2011 to address fishery concerns in the Banks Lake 

Feeder Canal at the John W. Keys III Pump Generating Plant at Grand Coulee Dam (Svoboda 

2011). Fish in Banks Lake tended to congregate in the feeder canal during pumping operations to 

feed when water is brought up from Franklin D. Roosevelt Lake by the pumping units. If the mode 

of operation quickly reversed from pumping to generating, fish were entrained through the feeder 

canal and into the generating units. Due to pressure changes within the pump-generator unit 

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runners, a high level of mortality occurs. Species of interest in Banks Lake included Lake Whitefish 

Coregonus clupeaformis, Smallmouth Bass, Walleye, Rainbow Trout, Common Carp Cyprinus carpio, 

Kokanee Salmon O. nerka, and Yellow Perch Perca flavescens. A 357-ft-long bar rack with 1-inch 

spacing was proposed in the feeder canal for the exclusion of adult fish. Since water would flow in 

both directions in the feeder canal daily, areas of the screen clogged during generation were expected 

to dislodge when pumping resumed. 

Applicability 

Physical barrier screens in Lake Powell would need to be very large in horizontal extents for a flat 

plate screen, or would require a large number of cylindrical screens to meet the required discharge 

capacity. Fixed screens would not be possible with variable water surface elevations in the reservoir, 

so the system would need to be moveable and removable and be adjustable with water level. 

Although highly effective at reducing entrainment, physical barrier screens are susceptible to debris 

clogging and biofouling, including invasive mussel attachment. Screens must be inspected and 

cleaned regularly. Recreational impacts would be minimal because a physical barrier would be 

located within the forebay. Due to the capacity, extents, and variable water level, there is no 

identified practical application of physical barrier screens in the reservoir at Glen Canyon Dam. 

Closed conduit screens (e.g., Eicher, Modular Inclined Screens (MIS)) could be used to generate 

impact mortality in fish passing through the penstock with a smaller screening footprint. However, 

the potential for screen clogging would be high and the subsequent increase in head loss at the 

turbine and subsequent negative impacts on power production limit practical application of this 

technology. 

Barrier Nets 

Description 

A fish exclusion barrier net is installed to allow water to pass through while physically blocking the 

movement of fish larger than the net open area. Net open area is selected based on the size of the 

fish desired for exclusion while considering debris accumulation and cleaning requirements. Fish 

nets may include upstream floating booms to limit floating debris collection on the net. Nets can be 

installed and removed seasonally or left in place. Nets must be inspected regularly for integrity. 

Related Examples 

A fish exclusion barrier net was installed at Lovewell Dam by the Kansas Department of Wildlife, 

Parks, and Tourism. The purpose of the net was to reduce the loss of fish from the reservoir during 

periods of canal outlets works discharges and/or lower operational releases through the spillway. 

Due to concerns about installation of a fish exclusion barrier net upstream of dam components, the 

Bureau of Reclamation conducted a Risk Analysis in 2012 to review potential dam safety and 

operations and maintenance issues associated with the barrier net. The installation of the barrier was 

approved. A net with 0.25-inch aperture designed by Mackworth-Enviro Aquatic Barrier & 

Screening Solutions was designed to exclude juvenile and adult Walleye, Crappie Pomoxis spp., and 

Gizzard Shad Dorosoma cepedianum (Mackworth Aquatic Environmental Systems 2012). The 430-ftlong, 21-ft-maximum height net successfully excluded fish during 3 years of operation, however, the 

flotation and netting deteriorated due to winter ice conditions and wind. To extend performance life, 

the barrier would have needed to be removed in September following the irrigation season and then 

reinstalled in April prior to first releases. Twice annual removal and reinstallation would have 

required significant personnel and resources. The barrier also caused unintended consequences to 

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fish populations. About ninety-five percent of the retained fish were gizzard shad and overabundant 

numbers of gizzard shad in the reservoir competed with young sportfish for food resources. 

A fish exclusion spillway net was installed in 1999 at Highline Lake near Loma, Colorado as part of 

the Upper Colorado River Endangered Fish Recovery Program’s effort to keep non-native 

Smallmouth Bass and other non-native species from spilling out of the reservoir into the Colorado 

River where they prey on four native fish — Humpback Chub, Bonytail Chub, Colorado 

Pikeminnow, and Razorback Sucker. The Highline Lake spillway net is 363 feet wide, 19 feet deep, 

has a dry weight of 1,400 pounds, and mesh openings of 0.25 inches (Martinez 2001). It is fabricated 

of a high-tech sturdy polyethylene fiber called Dyneema, a material well suited for the net due to its 

resistance to abrasion, light degradation, and fatigue without special coverings or coatings (Martinez 

2002). The net durability has resulted in the spillway net being left in place year-round, even during 

winter when the lake is frozen (Martinez 2001). Since the original installation in 1999, the Highline 

Lake spillway net has been replaced in 2006, 2014, and 2022. Colorado Parks and Wildlife conducts 

inspection and cleaning with a dive team at an annual cost of about $10,000-$20,000. The dive team 

conducts underwater inspections and cleanings approximately four-to-five times per year due to 

algal and debris buildup on the spillway net. Sampling efforts by the Colorado Parks and Wildlife 

show that the effectiveness of the net was favorable in controlling escapement of resident and 

stocked non-native fishes from the reservoir. Catch rates between the net and the spillway, however, 

were higher in 2021 and 2022 than previous years, likely due to net condition and canal surges that 

partially submerged the net (Upper Colorado River Endangered Fish Recovery Program 2022). 

A similar fish exclusion spillway net was installed at Elkhead Reservoir near Craig, Colorado in 2016 

as part of the Upper Colorado River Endangered Fish Recovery Program to prevent escapement of 

Northern Pike Esox lucius and Smallmouth Bass into the Yampa River. The Elkhead Reservoir net is 

575-feet long and 30-feet deep and is also fabricated with the polyethylene fiber Dyneema. The net 

is fully exclusionary, extending from the reservoir bottom to the water surface and can remain 

effective for a spillway release of up to 2,000 ft3/s. The $1.3M net was fabricated by Pacific Netting 

Products (www.craigdailypress.com/news/net-installation-begins-at-elkhead-reservoir/). It is 

secured to the reservoir bottom via anchors. A 2-foot diameter 800-foot long foam-filled debris 

boom with a 4-foot skirt extending beneath the water surface is situated upstream of the spillway net 

to reduce wave action and protect the net from large logs and other debris. The net is not removed 

seasonally. Colorado Parks and Wildlife conducts inspection and cleaning with a dive team at an 

annual cost of about $10,000-$20,000. Four underwater inspections and cleanings were completed in 

2021 and four inspections and cleanings are expected in 2022. There are no Dreissenid mussels in 

Highline Reservoir and Elkhead Reservoir, so biofouling is limited to algal growth. The Elkhead 

Reservoir spillway net has no anticipated near-time replacement timeline. Sampling efforts show that 

the Elkhead Reservoir net is effective at substantially reducing escapement of non-native fish from 

the reservoir, but not eliminating it. 

Floating nets near the spillway gates at Canyon Ferry Dam in Montana were considered by the 

Montana Fish, Wildlife, and Parks to prevent non-native stocked Walleye from passing over the 

spillway to the downstream blue ribbon trout stream. Floating nets were not installed due to dam 

safety concerns regarding the ability to sufficiently anchor the netting system and costs associated 

with the project. 

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Applicability 

Fish exclusion nets have been installed at a few locations with some success. All identified projects 

with fish exclusion nets were fully exclusionary with the net extending from the reservoir bottom to 

the water surface. Due to fabrication, inspection, and anchoring requirements in the deep reservoir 

depths at Glen Canyon Dam, the fish exclusion net would need to be floating in about the upper 30-

50 ft section of the water column. If an exclusion net were installed at the log boom location, the net 

would need to be approximately 1,000 ft long. Nets are installed in sections, so the length of the net 

is feasible but may produce notable installation and maintenance challenges. 

For similar projects, fish exclusion nets were installed once and left in place. Due to the extensive 

length of the net barrier and no icing concern at Glen Canyon Dam, the net may be able to stay 

installed if biofouling can be managed and invasive mussels do not cause occlusion of the openings. 

Nets installed in other locations were inspected and cleaned several times per year to maintain 

effectiveness. If the net is left in place during years with higher water levels, maintenance may 

become difficult. One of the winners of the Fish Protection Prize is currently testing an additive to 

the manufacturing process to make underwater nets susceptible to inspection using sonar 

instruments, so that nets can be inspected in any water turbidity by boat (Prometheus Innovations, 

LLC; https://americanmadechallenges.org/challenges/fishprotection/index.html). This technology 

may improve future inspection and maintenance opportunities at fish nets. 

Installation of a net upstream of a dam creates infrastructure safety concerns. If the net dislodges, it 

could block spillways or outlets or become entrained into penstocks. For the Lovewell Dam 

application, the Bureau of Reclamation conducted a Risk Analysis to identify potential impacts to 

dam safety and operations and maintenance. It is reasonable to expect that a similar assessment 

would be required for installation of a barrier net at Glen Canyon Dam. 

Air Bubble Curtains and Underwater Acoustic Barriers 

Description 

Air bubble curtains are created when compressed air enters a linear air diffuser. The inner pressure 

releases bubbles through holes in the tubing line which forms a curtain of evenly dispersed bubbles. 

Air bubbles can be used for increasing oxygen, de-icing, debris collection, and sediment 

containment. In the context of fish deterrence, a continuous screen of bubbles in the water column 

creates an unnatural visual cue for fish to avoid. As a visual deterrent, air bubbles are limited by light 

penetration, especially due to turbidity. Air bubble curtains also produce ancillary acoustic and 

hydrodynamic fields that may deter fish. 

Underwater acoustic barriers are sound-based behavioral deterrents. Fixed submerged sound 

projector arrays create sound waves at a certain frequency and amplitude to induce an avoidance 

response in fish. Bureau of Reclamation (2006) summarizes field application experience with sound 

systems from EPRI 1999. 

Related Examples 

Tennessee Valley Authority has been installing aeration systems in the southeast United States on 

hydropower projects since the 1970s. An oxygen diffuser system in the forebay of Tennessee Valley 

Authority’s Douglas Dam near Knoxville, Tennessee was installed to increase dissolved oxygen 

levels (Mobley and Brock 1995). Although the purpose of the aeration system is not for fish 

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exclusion, the scale of the installation makes this project relevant to Lake Powell. Liquid oxygen is 

delivered by truck to an on-site bulk oxygen storage facility and gaseous oxygen is distributed to 12 

miles of porous hoses attached to a frame. The hoses float approximately 20 ft above the reservoir 

bottom by using weights adjusted to match the bottom topography. 

In 2002, a hypolimnetic oxygenation system was installed at Upper San Leandro Reservoir near 

Oakland, California to address algal blooms and taste and odor complaints (Mobley 2003). Similar to 

Tennessee Valley Authority aeration designs, the single-line diffuser extends 8,500 ft along the 

centerline of the reservoir with two sections of porous hose. Stainless steel cable attaches to anchors 

placed at the reservoir bottom with a buoyancy pipe connected to the porous hose. Pure gaseous 

oxygen is supplied by a 6,000-gallon storage tank onsite. 

Laboratory research is being conducted on the use of oblique bubble screens as two-way dispersal 

barriers (Cupp et al. 2021). Oblique bubble screens are deployed across a channel at an angle to the 

flow (e.g., 45 degrees) to guide upstream-moving fish toward potential collection zones and to 

redirect downstream-moving particulates toward an active or passive collection point. After 

laboratory studies are complete, field tests are planned for 2023. 

A winner of Reclamation’s Improving Fish Exclusion from Water Diversions and Intakes prize 

competition (https://www.usbr.gov/research/challenges/fishexclusion.html) and finalist in the Fish 

Protection Prize suggested using air currents to direct larvae and eggs from intakes though physical 

attachment to bubbles (TWB Environmental Research and Consulting; 

https://americanmadechallenges.org/challenges/fishprotection/index.html). 

A laboratory study conducted by Zielinski and Sorensen (2016) used a unidirectional bubble curtain 

to reduce passage of Silver Carp Hypopthalmichthys molitrix, Bighead Carp H. nobilis, and Common 

Carp. Passage was reduced in the experiment channel by 73–80% for all three carp species. The air 

bubble curtain produced sound between 100 and 1,000 Hz at 145 dB which was within the hearing 

range of the tested carp. A study by Zielinski et al. 2014 indicates that the addition of speaker arrays 

and lighting to an air bubble curtain created avoidance responses based on sound and fluid motion 

rather than visual cues. Researchers conclude that sound produced by the bubble curtains is most 

likely responsible for carp deterrence as bubble plumes efficiency can be limited by ambient light 

(Zielinski et al. 2014). 

A study by Dennis et al. (2019) found that when an air curtain was coupled with sound, the 

combined stimulus was more effective in blocking Bighead Carp, Common Carp, and Largemouth 

Bass. They also concluded that response to behavioral sound barriers is species-specific and soundspecific, such that a proprietary sound was most effective in deterring carp, but not Largemouth 

Bass since they have less sensitive hearing than carp. 

After successful pond studies, an experimental underwater acoustic deterrent system was tested in 

2021 on the Mississippi River near Keokuk, Iowa in the downstream approach of lock no. 19 (Cupp 

et al. 2021). Studies are ongoing to determine the effectiveness of the 16 underwater transducers in 

deterring invasive carp. 

The Brandon Road Interbasin Study is a complex plan by the U.S. Army Corps of Engineers Rock 

Island District to prevent upstream movement of invasive carp and other aquatic nuisance species 

into the Great Lakes from the Illinois Waterway. Engineering and design initiated in December 

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2020. Deterrence measures will be installed in sequence, such that species are exposed to one 

deterrent after another. Technologies to prevent the upstream passage of delirious species includes a 

flushing lock, engineered channel with electric barrier, underwater acoustic deterrent system, and air 

bubble curtain. Studies completed prior to construction will be used to define specific design 

parameters. 

Applicability 

The Tennessee Valley Authority installations show that there is precedent for very long aeration 

systems. Due to the significant water depth in Lake Powell, it is not feasible to install an air bubble 

curtain at the reservoir bed or to drive piles to fasten the air supply line. An air bubble curtain would 

need to be suspended by buoys with weights and/or bottom anchoring to prevent floating. If the air 

bubble curtain is installed at a specific depth from the surface, fish could move lower in water 

column to pass the behavioral curtain. 

Air bubble curtains can create significant upwelling of the surrounding fluid which induces localized 

mixing. There may be implications to water temperatures or dissolved gas levels. The effectiveness 

of air bubbles in limiting non-native fish movement in Lake Powell is uncertain. 

Underwater acoustic deterrents have shown promise for deterring invasive Carp since they have 

specialized hearing abilities (Popper 1972; Lovell et al. 2006). Sound systems have been inconsistent 

in generating fish exclusion and are more effective at some sites with certain fish species. Either 

independently, or in combination with an air bubble curtain, the effectiveness of acoustic deterrents 

in deterring non-native species of concern in Lake Powell is uncertain. Like the air bubble line, 

acoustic transducers would likely need to be suspended from the water surface rather than mounted 

at the reservoir bed. 

Large-scale compressed gas injection for bubble barriers and underwater acoustic barriers require 

continuous energy to run using land-based infrastructure. Additional maintenance activities will be 

required such as dive inspections and cleaning. Infrastructure installed in the forebay may be 

susceptible to invasive mussel attachment, which may reduce the performance of the device. 

Multi-Stimulus Barriers 

Description 

Multi-stimulus barriers use several types of behavioral deterrents in combination to create an 

avoidance response by fish. These multi-modal systems may incorporate an air bubble curtain, 

sound signals, and directional strobe light in a single barrier. Like air bubble and acoustic barriers, 

multi-stimulus barriers are installed on or near the bed of the water body. Applications have 

included exclusion at hydroelectric intakes, limiting passage of invasive fish, and guiding 

downstream-migrating fish away from diversions and canals. 

Related Examples 

A commercially-available Bioacoustic Fish Fence by Fish Guidance Systems was temporarily 

installed in the Sacramento River at Georgiana Slough in 2011 and 2012 to prevent downstreammigrating anadromous fish species including winter-run, spring-run, fall-run, and late fall-run 

Chinook Salmon O. tshawytscha and Steelhead O. mykiss from entering Georgiana Slough. The barrier 

was 630-ft-long with frames consisting of 600 sound projectors, 12 high-intensity modulated light 

bars, and perforated bubble pipe. The frame was attached to driven piles to adjust for the uneven 

bed contours with the bioacoustics fish fence situated approximately 12 ft below the high tide water 

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level. During the 2011 study period, the Bioacoustic Fish Fence reduced the number of salmon 

smolts that would have been entrained by approximately two-thirds with 22.1% entrainment with 

the barrier off versus 7.4% entrainment with the barrier on (California Department of Water 

Resources 2012). High discharge was identified as an important predictor of fish behavioral 

response. High turbidity levels likely limited the use of visual cues created by the light intensity. The 

California Department of Water Resources plans to install and operate a Bioacoustic Fish Fence at 

the Georgiana Slough junction for 8 years from 2022 to 2030. 

A Bioacoustic Fish Fence consisting of sound, bubbles, and high-intensity light-emitting diodes was 

also installed upstream of the divergence of the San Joaquin River and Old River in California in 

2009 to deter anadromous juvenile salmonids from entering Old River (Bowen 2009). The barrier 

was 367 ft long at a 24-degree angle incident to the San Joaquin River. The barrier components were 

attached to a truss-style frame affixed to driven pilings. 

In another installation, a BioAcoustic Fish Fence including sound, light, and bubbles was installed 

on the downstream side of Barkley Lock on the Cumberland River in Kentucky in 2020 to reduce 

movement of invasive carp through the lock chamber. The Bioacoustic Fish Fence will be installed 

as a three-year field study until fall 2023. Approximately 1,100 Silver Carp and 225 native fish were 

implanted with acoustic transmitters and an additional 1,500 transmitters are planned to be 

implanted later in the study, providing a robust data set to assess the efficacy of the barrier. 

Preliminary data show that the Bioacoustic Fish Fence is effective in reducing, but not eliminating, 

fish passage at the barrier location (U.S. Fish and Wildlife Service 2022). 

Applicability 

A multi-stimulus barrier may provide the best opportunity for behavioral deterrence due to the 

variety of stimuli. Multi-stimulus barriers are often fixed to the bed of the river or reservoir or 

attached to specially driven piles to support the weight of the components within the frame. No 

examples of multi-stimulus barriers suspended in the water column were identified, which would 

likely be required for an in-reservoir installation at Glen Canyon Dam. Like the air bubble or 

acoustic deterrent system, fish could move lower in the water column to pass a multi-stimulus 

behavioral barrier if it is suspended in the water column. 

There are no impacts to operations or hydropower production with a multi-stimulus behavioral 

barrier. Multi-stimulus barriers increase maintenance requirements by requiring dive inspection and 

cleaning. Infrastructure installed in the forebay will be susceptible to invasive mussel attachment, 

which may reduce the performance of the device. Large-scale gas injection and sound modulation 

requires land-based infrastructure and continuous energy. 

Carbon Dioxide Barrier 

Description 

Infusion of carbon dioxide into water has shown promise as a chemical fish deterrent. This type of 

system creates a non-physical means to reduce the movement of fish while not inhibiting river flow. 

Fish respond strongly to carbon dioxide by avoiding treated areas or becoming immobilized through 

narcosis. Carbon dioxide is nonselective to fish size and species. In 2019, carbon dioxide was 

registered with the U.S. Environmental Protection Agency as a pesticide for carp. 

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Related Examples 

Research has been conducted on the use of carbon dioxide injection into navigation locks to deter 

invasive fish from swimming upstream while not impeding vessel passage or lock operation. Zolper 

et. al describe the performance of wall- and floor-based carbon dioxide-infused water injection 

manifolds in terms of mixing time, mixing homogeneity, injection efficiency, and operational power 

requirements at a concrete test pond in La Crosse, Wisconsin (2019) and at a navigational lock 

chamber on the Fox River near Kaukauna, Wisconsin (2022). Results show that mixing must extend 

to all regions of a lock to prevent passage of invasive carp. Study data can be used to guide design 

and improve performance of carbon dioxide infusion systems. 

A study by Cupp et al. (2017) shows that carbon dioxide altered Silver Carp and Bighead Carp 

movement in outdoor ponds. In 2018, a field evaluation was completed to reduce fish abundance 

near culverts (Cupp et al. 2018). Fish abundance was 70-95% lower when target carbon dioxide 

concentrations of 100 mg/L could be achieved. In 2020, Cupp et al. completed a telemetry study to 

evaluate behavioral avoidance of invasive carp in a large U-shaped pond to carbon dioxide. On 

average, 58% of test fish were restricted in movement at 121 mg/L and 78% were restricted in 

movement at 213 mg/L. 

The Tracy Fish Collection Facility in Tracy, California is exploring the use of carbon dioxide to 

remove adult and juvenile striped bass from the facility to reduce predation losses (Wu et al. in 

draft). In this application, dry ice is inserted into a confined channel. As striped bass move 

downstream to avoid the carbon dioxide, they are collected in holding tanks and removed from the 

facility. 

Applicability 

Carbon dioxide has shown some effectiveness in influencing fish movement in controlled 

environments in confined locations such as ponds and locks. In these environments, full mixing is 

required to all stagnation regions to prevent passage of invasive fish. Continued research is being 

conducted on direct gas injection systems that are designed for flowing water. No applications were 

identified where carbon dioxide was being injected in the form of a long barrier wall for fish 

deterrence in open water which is the most likely application at Glen Canyon Dam. Large-scale gas 

injection requires land-based infrastructure and continuous energy. This type of system could hang 

from a buoy line with weights or bottom anchors. Diffused gas may create upwelling of the 

surrounding fluid which induces localized mixing and elevated carbon dioxide levels will reduce the 

pH of the water. Carbon dioxide could also be injected directly upstream of the penstock trashracks. 

Vermeyen (2011) documented near-field velocity measurements adjacent to the trashrack bars at the 

penstock centerline elevation as 1.64 ft/s during a release of 3,600 ft3/s. Fish that sense the barrier 

may be able to avoid entrainment, but narcotized fish would be drawn through the penstocks. 

Infrastructure in the reservoir forebay would typically be susceptible to invasive mussel impacts, but 

carbon dioxide has been shown to impede Dreissenid mussel attachment and survival (Waller et al. 

2021) and may also impede Colonial hydroid biofouling (Brown et al. 2016). 

Floating Barriers 

Description 

Floating barriers such as plates and curtains may be used to induce behavioral guidance. Since these 

barriers do not extend to the bed and may contain gaps at seams, they are not true physical barriers. 

These barriers are attached to floating buoys and extend some distance in the water column. 

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Related Examples 

In 2014, a physical barrier called a Floating Fish Guidance Structure by Worthington Waterway 

Barriers was tested on the Sacramento River at Georgiana Slough as a guidance structure to prevent 

downstream-migrating anadromous fish species from entering Georgiana Slough. A typical Floating 

Fish Guidance Structure is made up of floating buoys that support vertically submerged solid metal 

plates which are designed to induce behavioral guidance. Separate plate sections are linked together 

and a flexible rubber material attached between the plates to prevent gaps. The Floating Fish 

Guidance Structure used at Georgiana Slough was about 361 ft long with steel sections 20 ft wide 

and 5 ft deep. A 10 ft panel depth was considered optimal, but could not be tested due to low water 

levels and a modeled panel submergence guidance of 50% depth. Study results show that the 

Floating Fish Guidance System was partially effective at reducing entrainment into Georgiana 

Slough with a five-percentage point reduction in entrainment at an intermediate discharge 

(California Department of Water Resources 2016). 

Fixed submerged curtains have been used to control release flow temperatures at outlets and 

diversions to improve downstream fish habitat. Reclamation has installed flexible curtains at 

Whiskeytown Lake and Lewiston Reservoir in California for temperature control (Svoboda 2020). 

Specific application of fixed curtains to reducing fish movement could not be found. 

Applicability 

There is a buoy line installed in Lake Powell upstream of Glen Canyon Dam to prevent large 

floating objects from entering the forebay. It is possible that a floating barrier could be installed at or 

near the location of the buoy line, potentially with deeper panels deployed near the canyon walls to 

better contain littoral dwelling species such as Smallmouth Bass. There is no power requirement for 

floating barriers, so there is less ongoing operational cost. Floating barriers would require regular 

maintenance for inspection and repair. Floating barriers would be susceptible to fouling, particularly 

by invasive mussels and Colonial Hydroid, but functionality of the barriers may still be maintained 

even when fouled. Efficacy would be limited by fish swimming between gaps in the barrier or under 

the barrier. There would be no notable impacts to recreation due to installation in the forebay. 

Electrical Barriers 

Description 

Electric barrier design typically involves submerging two or more metal electrodes in a fixed location 

and applying a voltage between them. When electrical current passes between the electrodes, an 

electrical field is formed in the water. Fish in contact with the electrical field may experience various 

responses such as avoidance, electrotaxis (forced swimming), electrotetanus (muscle contraction), 

electronarcosis (muscle relaxation or stunning), or death (U.S. Geological Survey 2001). Maximum 

power transfer to the fish occurs when the water conductivity is equal to the conductivity of the fish 

(approximately 115 μS/cm). When ambient water conductivity is higher, more current is required to 

transfer the same amount of power to the fish. Large fish are generally more susceptible to electrical 

fields than smaller fish because more power is transferred for a given voltage gradient (volts per unit 

distance) over the length of the fish (Reynolds 1996). Commercially available electric barriers can be 

installed with electrodes as vertical drops suspended from a cable, attached to pilings, attached to 

buoys at the water surface, or suspended mid-depth in the water column or electrodes can be flushmounted on the river bottom in concrete. 

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Related Examples 

In 2012, a vertically suspended electric fish barrier was installed by the Delta-Montrose Electric 

Association at the east end of South Canal to prevent downstream passage of Rainbow Trout and 

Brown Trout Salmo trutta from the Gunnison River into the South Canal Hydroelectric Plants. The 

vertical electrodes hang from an overhead cable for a total width of 74 ft, water depth of 16 ft, 

conductivity of 180 μs/cm and water velocities between 0.66-2.3 ft/s. Mark-recapture monitoring 

conducted by Colorado Parks and Wildlife show that 1.3% of tagged Rainbow and Brown Trout 

were recovered downstream of the barrier. Kowalski (n.d.) reports that the barrier was effective at 

limiting passage of larger fish, but not age 0, age 1, or age 2 trout. 

Dozens of bottom-mounted electric barriers have been installed to limit upstream movement of 

fish. At Quilcene and Quinault National Fish Hatcheries in Washington and Eagle Creek National 

Fish Hatchery in Oregon, upstream-migrating salmon are blocked from upstream movement and 

diverted to the hatchery entrance. Electric barriers have also shown effectiveness in limiting the 

movement of invasive fish or the movement of fish into undesirable areas. Swink (1999) showed 

that an electric barrier greatly reduced the upstream migration of Sea Lamprey Petromyzon marinus in 

the Jordan River, Michigan with only 0-1.8% (95% confidence interval) passing. Only one of 130 

Common Carp released below the electric barrier in the Chicago Sanitary and Ship Canal passed 

upstream of the electric barrier (Sparks et al. 2010). Barring power outages or low-flow conditions, 

electric barriers in the Central Arizona Project successfully prevented grass carp from migrating 

upstream in canals (Clarkson 2004). 

A recent study by Meister et al. (2021) used an electrified bar rack to guide Spirlin Alburnoides 

bipunctatus and European Eel Anguilla anguilla to a bypass in a laboratory flume. Results showed that a 

wider electrified bar rack (51 mm clear spacing and 38 V pulsed direct current) produced similar 

protection efficiency to a bar rack with a smaller bar spacing (20 mm clear spacing). Various levels of 

injuries due to electrification were observed. 

Applicability 

Electric barriers could be considered for installation at several locations at Glen Canyon Dam 

including the reservoir forebay, at the penstock trashracks, and inside the penstocks. Due to the 

deep reservoir water depth, a forebay electric barrier would need to be surface mounted with 

vertically oriented electrodes in Lake Powell. The barrier length would need to be hundreds of feet 

long. Since electric barriers are size selective, the voltage gradient would need to be sufficiently high 

to produce an avoidance response in mid-sized fish, which may cause larger-bodied fish to respond 

in tetanus or narcosis and be entrained. Water conductivity measured at Wahweap in Lake Powell 

ranged from 897 to 1105 μS/cm in July 2022. Electric barriers must be set at a higher current to 

elicit a response from fish when the ambient water conductivity is greater than the approximate 

conductivity of fish (115 μS/cm). Electric fields can be disrupted by steel-hulled boats and power 

outages. An electric field generated in the reservoir would require constant power supply and land 

infrastructure. Worker safety precautions would be required in the forebay area. Alternately, the 

penstock trashrack bars could be electrified. Voltage gradient levels would need to be high enough 

between the 4-3/8-inch clear spacing to deter mid-sized fish at a distance where fish could avoid 

being drawn through the penstock intake. A velocity of 1.64 ft/s was measured adjacent to the 

trashrack bars (Vermeyen 2011). Larger-bodied fish that respond in tetanus or narcosis to an 

electrical field at the trashrack would be impinged on the trashrack or drawn through the penstocks. 

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An electrified section of pipe could be installed inside the powerplant to induce mortality in these 

fish prior to exit in the tailrace; however, the short exposure time may limit effectiveness. 

Other In-Reservoir Barriers 

Other types of in-reservoir physical barriers such as weirs, culverts, rock gabions, overshot and 

undershot gates, guide walls, and physical structures to create velocity barriers cannot be reasonably 

applied to deep reservoirs such as Lake Powell and will not be considered further. Other types of 

behavioral barriers include submerged velocity jets, flow alteration, olfactory stimulus, turbulence, 

infrasound, spaced louvers, hanging chains, chemicals, ozone, and pheromones; however, these 

technologies are unlikely to have high exclusion rates in the reservoir forebay. Underwater lights 

used independently would not have high efficacy during daylight hours. Seismic water gun arrays 

have been used to create concussive blasts that rupture fish swim bladders. Although the behavior 

of tested fish was altered, the method was not fully effective as a deterrent (Romine et al. 2015). 

Several theoretical concepts identified during the 2020 Fish Protection Prize and the 2019 

Improving Fish Exclusion from Water Diversions and Intakes prize competition were reviewed. 

Sound and light barriers based on sweeping chirp signals and looming darkness, cavitation barriers, 

floating barriers using the Coanda effect to separate fish from water, electromagnetic longitudinal 

wave barriers, fish entrainment reduction structures to guide bottom-oriented fish, and subsurface 

withdrawal systems were either still theoretical concepts or were not fully relevant to the application 

at Lake Powell (https://americanmadechallenges.org/challenges/fishprotection/index.html). 

At Dam Options 

Deeper Water Withdrawal 

Description 

The river outlet works, located near the left abutment of Glen Canyon Dam, consist of two intake 

structures with trash racks, four 96-inch-diameter steel pipes, ring-follower guard gates, and hollowjet valves for flow regulation. The centerline of each river outlet intake is 96 ft below the centerline 

of the penstocks. Releasing water from deeper in the reservoir water column may prevent 

downstream passage of non-native fish that reside in the reservoir epilimnion. 

Applicability 

Results of a 2012 hydroacoustic survey show that most sampled fish were located in the top 14 m 

(45.9 ft) of the water column with the first 4 m (13.1 ft) of water having the highest densities of fish 

(Bureau of Reclamation 2012). Water releases through the outlet works may have benefits for 

preventing non-native fish from passing downstream. Any fish passing through the outlet works 

would encounter hollow-jet valves and high conduit velocities of approximately 50 ft/s (water 

velocity in penstock design is limited to 20 ft/s), which may limit downstream survival. Releasing 

water through the outlet works may increase periodic review maintenance activities but would have 

no recreational impact. Deeper water releases may also have benefits for passing cooler temperature 

flows downstream which may restrict establishment of non-native fish by inhibiting spawning of 

warmwater non-native species. 

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Water releases through the low-level river outlet works bypass the turbines. Power generation is not 

possible during river outlet works releases. Reclamation is currently conducting planning-level 

activities to identify potential concepts for hydropower generation at Glen Canyon Dam below the 

minimum power pool of elevation 3490 as a solution for potential drought relief. A recently 

completed Value Planning study (in draft, 2022) has identified several alternatives, including a bypass 

powerplant, a low-level power intake within the dead pool that connects to the existing powerplant 

penstocks, dead pool lake tap tunnel(s), and connection of outlet works conduits to the existing 

powerplant penstocks. Since a permanent solution to hydropower generation below minimum 

power pool may take more than 15 years (depending on the alternative selected for construction), 

other fish escapement solutions will be needed in the near-term. 

Turbine Mortality 

Description 

Fish passing through turbines are susceptible to direct blade strikes, pressure changes that rupture 

the swim bladder, and shear stress that can result in descaling, stripping of the protective mucus 

coating, and tissue tearing. Mortality rates can depend on broad range of variables such as species, 

life stage, size, pressure differential, diameter of intake pipe and turbine, number of blades, size and 

shape of blades, speed of blades, fish passage location within turbine, intake velocity, and 

entrainment duration. Mortality can be immediate, or injuries sustained during entrainment can 

result in delayed mortality. 

Related Examples 

A systematic review by Algera et al. (2020) confirmed that turbines and spillways increase the risk of 

injury and/or mortality for downstream passing fish compared to controls. They also reported that 

Francis turbines resulted in a higher immediate mortality risk than Kaplan turbines relative to 

controls (Algera et al. 2020). Based on the supplementary meta-analysis data presented in Algera et 

al. 2020, the mean survival in Francis turbines is approximately 58.8% (for species other than eels), 

but survival values vary widely across species and size class. 

Electric Power Research Institute (1992) summarizes data showing that maximum survival of fish 

passing through Francis turbines is achieved near peak unit efficiency, mortality increases with head 

on the turbine, and smaller fish tend to have lower mortality rates, although larval fish mortality was 

not evaluated. 

Applicability 

Fish entrained in the Glen Canyon Dam penstocks will pass through Francis turbines. Fish mortality 

due to turbine passage will reduce the number of non-native fish that survive passage downstream 

of Glen Canyon Dam, but some survival is expected. Utah State University researchers are 

deploying a Sensor Fish in 2022 to measure pressures, stresses, and velocities that live fish may 

experience when passing through the turbines at Glen Canyon Dam. Results will provide more 

information on the likely survival of fish through the turbines. A winner of the Fish Protection Prize 

is currently developing a technology to direct fish to streamlines in the low-velocity region near the 

turbine hub to minimize the likelihood of severe strike injury and mortality (Natel Energy; 

https://americanmadechallenges.org/challenges/fishprotection/index.html). In a reverse 

application, guidance to the areas of highest strike may increase mortality. Fish passage through the 

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Francis turbines has no operational, power, maintenance, or recreational impact. However, the 

effectiveness of turbine mortality as the sole fish exclusion technology will not meet project goals. 

Energy Dissipating Valve 

Description 

Energy dissipating valves are used to control flow in water distribution and water treatment systems. 

Energy dissipating valves can be used on reservoir outlets for in-line pressure reduction, flow 

control, and energy dissipation of outflow water to minimize downstream scouring of the outlet 

structure and river bed. Commonly used in areas with a high pressure drop, the sleeve valve can 

discharge to the atmosphere, or to a submerged outlet downstream. 

Related Examples 

A Pratt energy dissipating sleeve-valve model 711 (Henry Pratt Company) was installed near the 

terminal end of the 48-inch-diameter reservoir discharge pipe at Ridges Basin Dam in Durango, 

Colorado (Bark et al. 2014). The sleeve valve consisted of opposing tapered nozzle holes at 0.63 inch 

diameter in a helical pattern. The purpose of the sleeve valve was to eliminate fish and fish embryo 

survival from Lake Nighthorse in the discharge water to limit negative impacts to downstream native 

fish. 

During testing, fish were subjected to passage through the 0.63-inch holes of the energy dissipating 

valve. Survival of Fathead Minnow Pimephales promelas (post-larval to adult < 75 mm), Bluegill 

Lepomis macrochirus (age-0 < 50 mm), Largemouth Bass Micropterus salmoides (age-0 and age 1+ < 75 

mm), and White Sucker Catostomus commersonii (age-0 < 75 mm and age-1+ at 75-125 mm) into the 

discharge water was completely eliminated at a discharge pressure of 62 psi and reduced to less than 

1 percent at pressures equal to or greater than 50 psi. Rainbow Trout embryo survival (eyed stage 4 

to 5 mm) was reduced to 12 percent at the maximum pressure tested of 71 psi, but intact eggs could 

not be destroyed at any of the reservoir elevations and pressures tested. 

Applicability 

Installation of an energy dissipating valve on the downstream penstock at Glen Canyon Dam will 

likely eliminate most fish survival. This type of technology would have some maintenance and 

cleaning requirements and no impact to recreation. However, installing an energy dissipating sleeve 

valve on the downstream penstocks will have impacts to power production due to increasing 

headloss in the penstock pipe. Calculations should be made to better quantify projected losses to 

power production with installation of an energy dissipating valve. 

Other At Dam Options 

It is possible that carbon dioxide or electricity could be applied at lethal dose inside penstocks, 

however this conceptual approach to inducing mortality has not been researched in a high-velocity 

in-pipe application. Dose concentration and retention time would need to be determined for flowing 

pipes and narcotized fish may survive passage. With carbon dioxide injection, there may be impacts 

to downstream water quality. In a similar type of application, ultraviolet treatment in cooling water 

systems have been studied at Davis Dam and Parker Dam to reduce settlement and increase 

mortality of larval quagga mussels (Pucherelli and Claudi 2017, Pucherelli et al. 2018). 

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Downstream Removal 

Manual Collection and Removal 

Description 

Non-native fish that survive turbine passage at Glen Canyon Dam could be collected and manually 

removed from the Colorado River downstream of the dam. A physical or non-physical barrier could 

be installed to guide fish into a sorting facility such that undesirable fish can be removed. Picket 

barriers, inflatable weirs, louvers, and other physical barriers along with multi-stimulus behavioral 

barriers are possible river guidance system options. Alternately, non-native fish could be targeted for 

boat-based removal efforts through continuous electrofishing or netting. 

Related Examples 

Reclamation’s Tracy Fish Collection Facility diverts and salvages fish from Sacramento-San Joaquin 

Delta water prior to export by the C.W. “Bill” Jones Pumping Plant to the southern San Joaquin 

Valley. The primary channel consists of a series of louvers, or vertically aligned metal slats, 

positioned at 1-inch spacing that creates turbulence that fish avoid. Fish move through one of four 

bypass pipes into a secondary channel where further dewatering occurs. Fish are collected in holding 

tanks and placed into trucks for transport away from the pumping plant. 

Washington Department of Fish and Wildlife and the Confederated Tribes conduct targeted boatbased suppression efforts to slow the downstream movement of Northern Pike in the Columbia 

River Basin. The agencies target known spawning locations and remove Northern Pike with gillnets. 

The Upper Colorado River Endangered Fish Recovery Program and the San Juan River Basin 

Recovery Implementation Program have conducted non-native fish removal for almost 30 years at 

an increasing scale and a current cost of up to $2 million per year based on annual workplans for 

each program (Upper Colorado River Endangered Fish Recovery Program and San Juan River Basin 

Recovery Implementation Program 2022). While the number of non-native fish, including Northern 

Pike and Smallmouth Bass, have been reduced, which is beneficial to the native and endangered 

fishes, the elimination of non-native fish is not expected or possible (Martinez et al. 2014). 

Applicability 

The Colorado River is contained by steep canyon walls downstream of Glen Canyon Dam. Access 

to the river is available at Lees Ferry which is located approximately 15 miles downstream of Glen 

Canyon Dam. A river-spanning barrier would have significant impact on recreation. Effectiveness of 

barriers for guidance of downstream-moving fish is variable and would be impacted by boat passage. 

Fish collection would not be species-selective and all native and non-native fish would be collected 

for sorting. Sorting facilities would be labor and cost intensive since personnel would be required to 

operate them daily. Manual collection and removal with electrofishing or netting would also be labor 

and cost intensive. In the Upper Colorado River Basin, electrofishing removal efforts have been 

successful in reducing Smallmouth Bass densities, but in years when environmental conditions are 

favorable, population increases have the potential to overwhelm removal efforts (Breton et al. 2014). 

Other Downstream Options 

Fish entrainment outflow tests were conducted at Blue Mesa Reservoir in 1994-1996 (Mueller and 

Hiebert 1997). Sieve nets were installed in the stoplog slots directly at the penstock exit to collect 

18 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

fish that passed through the dam. The net installation was temporary during the duration of the test 

and was not intended for permanent application. Inducing mortality through physical impact on 

grates or energy dissipating blocks may reduce survival, but not for all size classes. Preventing 

downstream movement using engineered drop structures is not viable option at Glen Canyon Dam 

due to the river gradient. 

Discussion 

Preventing downstream movement of non-native fish from Lake Powell to the Colorado River 

downstream of Glen Canyon Dam is a difficult problem without a definitive solution. There is no 

clear alternative that can fully eliminate fish escapement without impact to operations, power 

production, maintenance, and recreation. Table 1 summarizes the assessment of alternatives based 

on applicability to Glen Canyon Dam. 

In-reservoir barrier options are exclusion devices that block the downstream movement of fish into 

the dam. Physical barrier screens are the more effective way to prevent passage of fish, but 

installation of a full-scale physical barrier is not feasible at the vertical and horizontal scale of this 

reservoir application and cleaning requirements would be notable. Various floating barrier options 

(nets, solid plates, curtains) are more feasible in terms of scalability and some larger-scale 

installations exist in other locations, but these barriers will only limit passage in the upper water 

column for certain fish sizes and anchoring will be challenging. Behavioral barriers have advantages 

in terms of a more limited in-water footprint and flow impedance, but effectiveness by species is 

highly variable. Underwater acoustic barriers are most effective for hearing-specialist fish species 

such as carp. Response to air bubble barriers varies by species and is limited by visual cues. Multistimulus behavioral barrier may provide the highest likelihood of success due to the variety of 

stimulus. Although no examples of behavioral barriers suspended in the upper part of the water 

column were identified (aside from electrical barriers), it may be possible to design such a system for 

Lake Powell. Exclusion options on or near the trashracks are attractive in terms of targeting a more 

finite area, but trashrack-mounted technologies may not provide enough reduction in fish 

entrainment, particularly if fish are passively drawn through the trashracks (4-3⁄8 inch clear bar 

spacing) based on local velocity or fish are immobilized by the barrier and transported through the 

penstocks. For all reservoir forebay installations, colonization by invasive mussels and Colonial 

Hydroid will increase inspection and maintenance needs and may disrupt barrier performance if 

barrier components are occluded or weighed down. Benefits of in-reservoir technologies include 

limited impacts to power production and recreation. 

Options located at the dam can limit passage or survival. Fish passing through the Francis turbines 

may experience immediate or delayed mortality. Although data is highly variable, studies show that 

some fish survival is expected. It is unlikely the turbine mortality will be fully effective as the sole 

solution to eliminate fish entrainment. Deeper water withdrawal through the river outlet works will 

likely reduce fish entrainment, but water releases through the outlet works would bypass the turbines 

and power production is currently not possible. Installation of an energy dissipating valve on the 

penstock pipe will limit fish survival, but this device will impact power production by increasing 

headloss in the penstock pipe. The effectiveness of applying carbon dioxide or electricity within the 

penstock at lethal dose to ensure mortality of fish that pass through is uncertain due to low exposure 

19 
 

 

time in the flowing pipes. Downstream barriers would require ongoing manual labor to collect and 

sort fish and would cause significant disruption to recreation, depending on the location of the 

barrier. Continuous electrofishing or netting would be labor and cost intensive. 

Based on the review of applicable projects, a forebay barrier net or multi-stimulus barrier may be the 

most likely alternative to limit impacts to power production, operations, and recreation while 

maintaining a reasonable level of entrainment protection. Deeper water withdrawal through the river 

outlet works or installation of an energy dissipating valve on the penstock pipe will also likely limit 

passage of non-native fish, but considerable impacts to power production are expected. Preferred 

alternatives should be evaluated in greater detail to identify possible installation layouts and design 

features, anchoring strategies, anticipated efficacy, impacts to power production, implementation 

timeframe, and initial and ongoing costs. 

20 
Table 1. Initial assessment of alternatives to limit non-native fish escapement at Glen Canyon Dam. Alternatives with limited applicability to Glen Canyon Dam are not 

summarized. 

Possible 

Application 

Scalability Effectiveness Operational 

Impact and 

Loss of Power 

Production 

Inspection and 

Maintenance 

Requirements 

Recreational 

Impact 

In-Reservoir 

Barriers 

Physical Barrier 

Screens 

Installed in 

forebay, at 

trashracks, or in 

closed conduit. 

Large width and 

depth and large 

discharge capacity 

limit practical 

application of 

barrier screens. 

High for fish larger 

than the opening size 

of the screen. 

Trashrack screens 

and closed 

conduit screens 

would increase 

headloss due to 

debris clogging. 

Susceptible to 

debris clogging and 

biofouling, 

including mussel 

attachment, and 

must be regularly 

inspected and 

cleaned. 

Minimal, since 

barrier would be 

installed in 

forebay area not 

accessible to 

boaters and 

anglers. 

In-Reservoir Net Suspended from 

buoy line; 

independent 

installation 

across forebay. 

There is precedent 

for fish exclusion 

nets at large widths 

and relevant 

depths due to 

modular layout, 

but anchoring 

would be a 

challenge. 

Similar installations 

show that nets are 

effective at reducing 

entrainment for fish 

larger than the opening 

size, but not eliminating 

it. 

Headloss across 

the net should be 

minimal. 

Infrastructure 

safety concerns 

should be 

addressed if the 

barrier dislodges. 

Susceptible to 

debris clogging and 

biofouling, 

including mussel 

attachment, and 

must be regularly 

inspected and 

cleaned. Nets can 

be removed 

annually or left in 

place. 

Minimal, since 

barrier would be 

installed in 

forebay area not 

accessible to 

boaters and 

anglers. 

Air Bubbles Suspended from 

buoy line; 

independent 

installation 

across forebay. 

There is precedent 

for air bubble 

barriers at large 

widths and 

relevant depths 

due to modular 

layout, but 

anchoring or 

suspension would 

be a challenge. 

Uncertain; varies by 

species and limited by 

visual cues. May reduce, 

but not eliminate 

entrainment. 

Requires 

continuous 

energy to run. 

Infrastructure 

safety concerns 

should be 

addressed if the 

barrier dislodges. 

Limited in-water 

infrastructure, but 

may be susceptible 

to some debris and 

biofouling impacts 

and must be 

occasionally 

inspected and 

cleaned. 

Minimal, since 

barrier would be 

installed in 

forebay area not 

accessible to 

boaters and 

anglers. 

21 
 

 

Possible 

Application 

Scalability Effectiveness Operational 

Impact and 

Loss of Power 

Production 

Inspection and 

Maintenance 

Requirements 

Recreational 

Impact 

In-Reservoir 

Barriers 

(cont.) 

Underwater 

Acoustic Barriers 

Suspended from 

buoy line; 

independent 

installation 

across forebay. 

There is precedent 

for underwater 

acoustic barriers at 

large widths and 

relevant depths 

due to modular 

layout, but 

anchoring or 

suspension would 

be a challenge. 

Uncertain; varies by 

species; most effective 

for hearing-specialist 

fish species. May 

reduce, but not 

eliminate entrainment. 

Requires 

continuous 

energy to run. 

Infrastructure 

safety concerns 

should be 

addressed if the 

barrier dislodges. 

Limited in-water 

infrastructure, but 

may be susceptible 

to some debris and 

biofouling impacts 

and must be 

occasionally 

inspected and 

cleaned. 

Minimal, since 

barrier would be 

installed in 

forebay area not 

accessible to 

boaters and 

anglers. 

Multi-Stimulus Suspended from There is precedent May provide best Requires Limited in-water Minimal, since 

Barriers buoy line; 

independent 

installation 

across forebay. 

for multi-stimulus 

barriers at large 

widths and 

relevant depths 

due to modular 

layout, but 

anchoring or 

suspension would 

be a challenge. 

opportunity for 

behavioral deterrence 

due to multi-stimulus 

approach. May reduce, 

but not eliminate 

entrainment. 

continuous 

energy to run. 

Infrastructure 

safety concerns 

should be 

addressed if the 

barrier dislodges. 

infrastructure, but 

may be susceptible 

to some debris and 

biofouling impacts 

and must be 

occasionally 

inspected and 

cleaned. 

barrier would be 

installed in 

forebay area not 

accessible to 

boaters and 

anglers. 

Carbon Dioxide Suspended from No precedent for Effective in influencing Requires Limited in-water Minimal, since 

Barriers buoy line; 

independent 

installation 

across forebay; 

injection at 

trashracks to 

influence nearfield 

entrainment; 

lethal dose 

injection within 

penstock. 

carbon dioxide 

injection barriers 

in open, flowing 

water. 

fish movement in 

controlled 

environments (ponds, 

locks). Near-field 

effectiveness could be 

limited by narcotized 

fish being drawn 

through penstocks. 

continuous 

energy to run. 

Infrastructure 

safety concerns 

should be 

addressed if the 

barrier dislodges. 

infrastructure, but 

may be susceptible 

to some debris and 

biofouling impacts 

and must be 

occasionally 

inspected and 

cleaned. Biofouling 

may be less likely in 

the presence of 

carbon dioxide. 

barrier would be 

installed in 

forebay area not 

accessible to 

boaters and 

anglers. 

22 
 

Possible 

Application 

Scalability Effectiveness Operational 

Impact and 

Loss of Power 

Production 

Inspection and 

Maintenance 

Requirements 

Recreational 

Impact 

In-Reservoir 

Barriers 

(cont.) 

Floating Barriers Suspended from 

buoy line; 

independent 

installation 

across forebay. 

There is precedent 

for floating-type 

barriers at large 

widths and 

relevant depths, 

but anchoring 

would be a 

challenge. 

Uncertain. Not enough 

relevant examples 

identified. 

No power 

requirement. 

Infrastructure 

safety concerns 

should be 

addressed if the 

barrier dislodges 

Susceptible to 

debris clogging and 

biofouling, 

including mussel 

attachment, and 

must be regularly 

inspected and 

cleaned. 

Minimal, since 

barrier would be 

installed in 

forebay area not 

accessible to 

boaters and 

anglers. 

Electrical Barriers Vertically 

suspended 

electrodes in 

forebay via 

cable; electrified 

trashrack bars; 

lethal application 

within penstock. 

No precedent for 

required width and 

depth of forebay 

barrier. 

Effectiveness is size 

selective such that 

larger fish receive 

greater impact. Nearfield effectiveness 

could be limited by 

narcotized fish being 

drawn through 

penstocks. 

Requires 

continuous 

energy to run. 

Worker safety 

precautions 

needed in the 

forebay. 

Infrastructure 

safety concerns 

need to be 

addressed if the 

barrier dislodges. 

May be susceptible 

to some debris 

clogging and 

biofouling and must 

be regularly 

inspected. 

Electrified trashrack 

application may 

have less 

maintenance. 

Minimal, since 

barrier would be 

installed in 

forebay area not 

accessible to 

boaters and 

anglers. 

At Dam Deeper Water Release through No scalability Water withdrawal No hydropower Some periodic No recreational 

Options Withdrawal low-level river 

outlet works. 

concerns. below epilimnion will 

likely limit fish passage; 

conditions within 

conduit may limit 

survival. 

generation 

possible during 

outlet works 

releases; planning 

activities 

underway for 

future power 

generation below 

the minimum 

power pool. 

maintenance 

expected. 

impact. 

23 
 

 

 

Possible 

Application 

Scalability Effectiveness Operational 

Impact and 

Loss of Power 

Production 

Inspection and 

Maintenance 

Requirements 

Recreational 

Impact 

At Dam 

Options 

(cont.) 

Turbine Mortality Fish passage 

through Francis 

turbines will 

reduce fish 

survival. 

Mortality increases 

with head on 

turbine. 

Francis turbines have 

higher immediate 

mortality than Kaplan 

turbines; percent 

survival depends on a 

broad range of factors. 

Unlikely to induce 

mortality at a high 

enough rate to be used 

as the sole fish 

exclusion solution. 

Fish passage 

through the 

turbines will have 

no impact on 

operations or 

power generation. 

Minimal 

maintenance 

expected. 

No recreational 

impact. 

Energy 

Dissipating Valve 

Installed in 

downstream 

penstock. 

Likely scalable. High effectiveness 

likely. 

Energy 

dissipating valves 

will increase 

headloss in the 

penstock pipes 

with impacts to 

power 

production. 

Minimal 

maintenance 

expected. 

No recreational 

impact. 

Downstream 

Removal 

Manual Collection 

and Removal 

through Sorting 

Facility 

Physical or 

behavioral 

barrier installed 

across narrower 

section of river 

to guide all fish 

into a holding 

and sorting 

facility. 

There is precedent 

for physical and 

behavioral barriers 

and collection and 

sorting facilities at 

large widths and 

relevant depths. 

All fish will be 

collected; effectiveness 

is likely moderate and 

will be based on species 

and size class; 

effectiveness will 

depend on ability to 

keep barrier clean of 

debris 

Requires daily 

operation of new 

collection and 

sorting facility 

downstream of 

the dam. 

Behavioral 

barriers will have 

continuous power 

requirements. 

Susceptible to 

debris clogging and 

biofouling; 

behavioral barriers 

require less 

inspection and 

maintenance. 

Significant 

recreational 

impact; barrier 

would require 

boat passage 

depending on 

installation 

location. 

Manual Collection 

and Removal 

through 

Electrofishing 

Electrofishing or 

other active 

boat-based 

manual 

collection. 

Large-scale 

electrofishing 

programs are in 

place. 

Electrofishing can 

reduce densities, but 

favorable conditions 

for fish can overwhelm 

efforts. 

Requires daily 

boat-based 

suppression 

efforts. 

Minimal 

maintenance 

expected. 

No recreational 

impact. 

24 
 

 

 

 

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