Characterizing the fish assemblage of the Lake Powell forebay: 

identifying the potential for nonnative fish escapement through 

Glen Canyon Dam and into the lower Colorado River

Barrett Friesen, Phaedra Budy, Casey Pennock

Utah State University
Lake Powell Entrainment Update

October 2022

2022 Accomplishments

• Three sampling trips conducted

• March, June, August

• Gillnets: 138 net-nights, 1,135 fish captured

• Minnow traps: 276 trap-nights, 401 fish captured

• 13 Temperature and dissolved oxygen profiles conducted

• 59 Ichthyoplankton tows, 5 larval fish collected

• Installation of 10 station submersible ultrasonic receiver (SUR) network

• Began ultrasonic tag implantation

Upcoming

• Final sampling trip of 2022: late Oct

• Implantation of ultrasonic tags

• 2023: 4 sampling trips

• March 2023: Sensor Fish deployment

• Integration of hydroacoustic data with catch data
SUR network geometry
Acoustic tags

1 of 30 implanted

Focused effort in Oct/Nov to implant more

• Gillnets

• Trap net

• Angling
Study focuses on area near GCD

Regions:

1. Forebay

2. Confluence

3. Wahweap

(1)

(3)

(2)
Forebay temperature profiles show developing epilimnion 

with respect to penstock position

March 2022

March + June 2022

March + June + August 2022

Penstock centerline

Penstock centerline

Penstock centerline

Preliminary data
Forebay: depth of nonnative fish captured via gillnet: March 2022

Penstock centerline = 17 m depth

0-11m: Nonnative fish

Preliminary data
Forebay: depth of nonnative fish captured via gillnet: March 2022

Penstock centerline = 17 m depth

0-11m: Nonnative fish

Preliminary data

GZS

37%

STB

13%

WAE

50%

n = 8, CPUE = 0.4 fish/net-night

GZS: Gizzard Shad

STB: Striped Bass

WAE: Walleye
Penstock centerline = 19 m depth

0-14m: Nonnative fish

Forebay: Depth of nonnative fish captured via gillnet: June 2022

Preliminary data
Penstock centerline = 19 m depth

0-14m: Nonnative fish

CCF

17%

CRP

21%

GZS

24%

SMB

17%

STB

18%

WAE

3%

n = 66, CPUE = 3.7 fish/net-night

Preliminary data

Forebay: Depth of nonnative fish captured via gillnet: June 2022

CCF: Channel Catfish

CRP: Common Carp

GZS: Gizzard Shad

SMB: Smallmouth Bass

STB: Striped Bass

WAE: Walleye
Penstock centerline @ 20 m depth

0-16m: Nonnative fish

Forebay: depth of nonnative fish captured via gillnet: August 2022

Preliminary data
Forebay: depth of nonnative fish captured via gillnet: August 2022

Penstock centerline @ 20 m depth

0-16m: Nonnative fish

CCF: Channel Catfish

CRP: Common Carp

GZS: Gizzard Shad

SMB: Smallmouth Bass

STB: Striped Bass

WAE: Walleye

n = 84, CPUE = 4.7 fish/net-night

Preliminary data

CCF

12% CRP

10%

GZS

21%

SMB

20%

STB

33%

WAE

4%
Smallmouth Bass in the forebay

Smaller but more numerous later in the summer

June 2022

n = 11

Mean TL = 308 mm

Mean Weight = 377 g

August 2022

n = 17

Mean TL = 226 mm

Mean Weight = 160 g

Preliminary data
3 key takeaways

• In the winter when the reservoir is cold and mixed, gillnets yield only 

coolwater species in the forebay (Walleye, Striped Bass, Gizzard Shad)

• As the reservoir warms and stratifies, warmwater fish appear in the forebay 

epilimnion (Smallmouth Bass, Channel Catfish, Common Carp)

• Penstock position relative to epilimnion likely a major driving factor in 

entrainment risk of warmwater nonnatives (lower water levels increase 

entrainment risk)
Acknowledgments

Bureau of Reclamation

• Clarence Fullard

• Kerri Pedersen

• Mike Horn

• Mark McKinstry

Utah State University

• Phaedra Budy

• Casey Pennock

• David Rosenberg

• Gary Thiede

Glen Canyon Recreation 

Area

• Jeff Arnold

U.S. Geological Survey