Iowa DNR
Iowa DNR

ADBNet

Water Quality Assessments
Impaired Waters List

Lake Wapello IA 04-LDM-1035

Davis County S34T70NR15 7 mi. W of Drakesville.

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 3:09:51 PM by
Updated
11/24/2025 2:26:07 PM by
Use Support
Class A1
Recreation - Primary contact
Fully Supported
Class BLW
Aquatic Life - Lakes and wetlands
Fully Supported
Class C
Drinking Water -
Fully Supported
Class HH
Human Health -
Not Supported
Support Level
Not Supported
Impairment Code
5a - Pollutant-caused impairment. TMDL needed.
Cause Magnitude
Moderate
303(d) Listing Status
Continuing
Source
Unknown: Source Unknown
Source Confidence
N/A
Cycle Added
2014
Impairment Rationale
Fish consumption advisory in effect: no more than 1 meal/week
Data Source
Fish contaminant monitoring: Iowa DNR
TMDL Priority
Tier IV
No delistings for this assessment cycle.
Documentation
Assessment Summary

The Class A1 use was assessed (monitored) as “fully supported.” The Class BLW use was assessed (monitored) as “fully supported.” The Class C use was assessed (monitored) as “fully supported.” The Class HH (fish consumption) use was assessed as “not supported" based on fish tissue sampling data and due to the existence of a one meal per week consumption advisory for mercury for this lake.

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

21260001

Lake Wapello Beach

Iowa DNR

6

WQ

CY 2021-2024

22260001

Lake Wapello

Iowa DNR

6

FT

See Below

1310

Lake Wapello

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

21260001

6

10/14/14

14

13

22

NO

1 / 3

1 / 4

3 / 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

22260001

6

12 / 4

7.54

8.72

8.2

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

22260001

6

Chlorophyll a TSI

12 / 4

41

67

56

NO

MONITORED

FULL

22260001

6

Secchi TSI

12 / 4

42

64

50

NO

MONITORED

FULL

22260001

6

Total Phosphorus TSI

12 / 4

37

58

49

NA

NA

NA

22260001

6

Fixed suspended solids

12 / 4

1.7

3

1.9

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

22260001

6

Dissolved Oxygen

12 / 4

4.8

9.9

7.9

1

NA / NA

4

NO

MONITORED

FULL

22260001

6

pH

12 / 4

7.54

8.72

8.2

0

NA / NA

4

NO

MONITORED

FULL

22260001

6

Temperature

12 / 4

22.6

29.7

25.5

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

22260001

6

5

6.4324

92.04%

3.3082

28.35%

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

22260001

6

Ammonia

12 / 4

0.027

0.02

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

22260001

6

Inorganic nitrogen (nitrate and nitrite)

11 / 4

0.05

0.52

0.18

0.15

0

NO

MONITORED

FULL

22260001

6

pH

12 / 4

7.54

8.72

8.2

8.22

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)

1310

fillet

2013

channel catfish

5

40.8

0.13

<0.2

<0.6

1310

tissue plug

2013

largemouth bass

5

40.9

1.212

Support Level

Not

A one meal/week mercury consumption advisory for largemouth bass exists on this segment. Based on IR Methodology, the Class HH (fish consumption) use was assessed as “not supported.”


Monitoring and Methods
Assessment Key Dates
5/25/2020
Monitoring Start
9/18/2024
Monitoring End
8/1/2013
Fish Tissue Monitoring
Methods
150
Monitoring data more than 5 years old
200
Physical/Chemical Monitoring
260
Fish tissue analysis
340
Primary producer surveys (phytoplankton/periphyton/macrophyton)
420
Indicator bacteria monitoring