Iowa DNR
Iowa DNR

ADBNet

Water Quality Assessments
Impaired Waters List

Viking Lake IA 05-NOD-1407

Montgomery County S6T71NR36W 4 mi. E of Stanton.

This is a DRAFT assessment
Draft assessments may change without notice
Overall IR
5 - Water is impaired or threatened and a TMDL is needed.
Trophic
Eutrophic
Trend
Stable
Current Phase
Public Comment
Created
10/27/2025 3:10:15 PM by
Updated
11/24/2025 2:31:22 PM by
Use Support
Class A1
Recreation - Primary contact
Not Supported
Support Level
Not Supported
Impairment Code
5a - Pollutant-caused impairment. TMDL needed.
Cause Magnitude
Slight
303(d) Listing Status
New
Source
Agriculture
Source Confidence
Moderate
Cycle Added
2026
Impairment Rationale
Narrative criteria violation: aesthetically objectionable conditions
Data Source
Ambient monitoring: Iowa DNR-lakes
TMDL Priority
Tier IV
Class BLW
Aquatic Life - Lakes and wetlands
Fully Supported
Class C
Drinking Water -
Fully Supported
Class HH
Human Health -
Fully Supported
No delistings for this assessment cycle.
Documentation
Assessment Summary

The Class A1 use was assessed as "not supported" due to aesthetically objectionable conditions caused by algae blooms. The Class BLW use was assessed (monitored) as “fully supported.” The Class C (drinking water) use was assessed (monitored) as “fully supported.” The Class HH (fish consumption) use was assessed (monitored) as “fully supported” based on fish tissue sampling data.

Assessment Explanation

Data Sources:

Data Source

Data Source ID

Data Type

Data Age

Site ID

Site Name

Site Description

Iowa DNR

6

WQ

CY 2022-2024

21690001

Viking Lake Beach

Iowa DNR

6

WQ

CY 2021-2024

22690001

Viking Lake

Iowa DNR

6

FT

See Below

1337

Viking Lake

Viking Lake State Park

Class A1 - Indicator Bacteria:

Site ID

Data Source ID

# Samples per Year (2022/ 2023/2024)

2022 Geometric Mean

2023 Geometric Mean

2024 Geometric Mean

Violates Annual Geometric Mean?

# 2022 SSM violations / SSM Violations needed for impairment

# 2023 SSM violations / SSM Violations needed for impairment

# 2024 SSM violations / SSM Violations needed for impairment

Violates Annual SSM Significantly >10% Rule?

Assessment Type

Support Level

21690001

6

15/13/14

21

28

22

NO

2 / 4

2 / 4

2 / 4

NO

MONITORED

FULL

Class A1 - pH

Site ID

Data Source ID

# Samples / # Years

Minimum Value

Maximum Value

Mean Value

# Violations

Violations needed for impairment

Violates Significantly >10% Rule?

Assessment Type

Support Level

21690001

6

43 / 3

7.6

9.2

8.4

1

8

NO

MONITORED

FULL

22690001

6

12 / 4

7.53

9

8.17

0

4

NO

MONITORED

FULL

Class A1 - Lake TSI's

Site ID

Data Source ID

Parameter Name

# Samples / # Years

Minimum Value

Maximum Value

Median Value

Median TSI Violation?

Assessment Type

Support Level

22690001

6

Chlorophyll a TSI

12 / 4

37

72

65

YES

MONITORED

NOT

22690001

6

Secchi TSI

12 / 4

52

66

60

NO

MONITORED

FULL

22690001

6

Total Phosphorus TSI

12 / 4

37

61

57

NA

NA

NA

22690001

6

Fixed suspended solids

12 / 4

1.7

7

2.4

NA

NA

NA

Class BLW - Binomial Parameters:

Site ID

Data Source ID

Parameter Name

# Samples / # Years

Minimum Value

Maximum Value

Mean Value

# Violations

# Acute / Chronic Violations

Violations needed for impairment

Violates Significantly >10% Rule?

Assessment Type

Support Level

21690001

6

Dissolved Oxygen

43 / 3

4.37

13.11

8.43

2

NA / NA

8

NO

MONITORED

FULL

22690001

6

Dissolved Oxygen

12 / 4

3.4

10.9

7.1

2

NA / NA

4

NO

MONITORED

FULL

21690001

6

pH

43 / 3

7.6

9.2

8.4

1

NA / NA

8

NO

MONITORED

FULL

22690001

6

pH

12 / 4

7.53

9

8.17

0

NA / NA

4

NO

MONITORED

FULL

21690001

6

Temperature

43 / 3

18.3

29.5

26

0

NA / NA

8

NO

MONITORED

FULL

22690001

6

Temperature

12 / 4

18.5

29.2

24.3

0

NA / NA

4

NO

MONITORED

FULL

Class BLW - Lake Planktonic Cyanobacteria:

Site ID

Data Source ID

# Samples

Maximum Cyanobacteria Wet Mass

Maximum Cyanobacteria % Composition

Median Cyanobacteria Wet Mass

Median Cyanobacteria % Composition

Median Cyanobacteria Concentration = 75th Percentile

Assessment Type

Support Level

22690001

6

4

24.11310366

90.00%

5.865437478

59.95%

NO

EVALUATED

NA

Class BLW - Toxic Parameters:

Site ID

Data Source ID

Parameter Name

# Samples / # Years

Maximum Value

Mean Value

Median Value

# Acute / Chronic Violations

>1 Acute / Chronic Violation

Assessment Type

Support Level

22690001

6

Ammonia

12 / 4

0.073

0.03

0.02

0 / 0

NO

MONITORED

FULL

Class C - Binomial Parameters:

Site ID

Data Source ID

Parameter Name

# Samples / # Years

Minimum Value

Maximum Value

Mean Value

Median Value

# Violations

Violates Significantly >10% Rule?

Assessment Type

Support Level

22690001

6

Inorganic nitrogen (nitrate and nitrite)

11 / 4

0.05

0.3

0.13

0.11

0

NO

MONITORED

FULL

21690001

6

pH

43 / 3

7.6

9.2

8.4

8.4

1

NO

MONITORED

FULL

22690001

6

pH

12 / 4

7.53

9

8.17

8.23

0

NO

MONITORED

FULL

Class HH - Fish Tissue Sampling:

Site ID

Biopart

Year

Species

# in sample / # of samples

Avg Length (cm)

(Avg) Hg (ppm)

Chlordane (ppm)

Sum PCBs (ppm)

1337

fillet

2015

channel catfish

5

46.6

0.03

0.02

0.06

1337

tissue plug

2020

crappie spp.

10

27.5

0.21

1337

tissue plug

2019

largemouth bass

10

32.5

0.269

Support Level

Full


Monitoring and Methods
Assessment Key Dates
5/26/2021
Monitoring Start
10/1/2024
Monitoring End
9/2/2015
Fish Tissue Monitoring
8/18/2015
Fish Tissue Monitoring
7/1/2019
Fish Tissue Monitoring
7/1/2020
Fish Tissue Monitoring
Methods
200
Physical/Chemical Monitoring
260
Fish tissue analysis
340
Primary producer surveys (phytoplankton/periphyton/macrophyton)
420
Indicator bacteria monitoring