Iowa DNR
Iowa DNR

ADBNet

Water Quality Assessments
Impaired Waters List

Nelson Park Lake IA 06-BOY-1506

Crawford County S2T82NR41W 4 mi. WNW of Dow City.

This is a DRAFT assessment
Draft assessments may change without notice
Overall IR
1 - All designated uses are met.
Trophic
Mesotrophic
Trend
Stable
Current Phase
Public Comment
Created
10/27/2025 3:10:18 PM by
Updated
11/21/2025 3:15:24 PM by
Use Support
Class A1
Recreation - Primary contact
Fully Supported
Class BLW
Aquatic Life - Lakes and wetlands
Fully Supported
Class HH
Human Health -
Fully Supported
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 HH use was assessed (monitored) as "fully supported" based on fish tissue monitoring.

Assessment Explanation

Start Date: 05/27/2020 End Date: 09/03/2024

Data Sources:

Data Source

Data Source ID

Data Type

Data Age

Site ID

Site Name

Site Description

Iowa DNR

6

WQ

CY 2020-2024

22240001

Nelson Lake

Iowa DNR

6

FT

See Below

1319

Nelson Park Lake

Class A - Indicator Bacteria: No Data

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

22240001

6

15 / 5

7.7

8.7

8.3

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

22240001

6

Chlorophyll a TSI

15 / 5

42

74

59

NO

MONITORED

FULL

22240001

6

Secchi TSI

15 / 5

39

81

51

NO

MONITORED

FULL

22240001

6

Total Phosphorus TSI

15 / 5

49

85

60

NA

NA

NA

22240001

6

Fixed suspended solids

15 / 5

0.7

11

2

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

22240001

6

Dissolved Oxygen

14 / 5

4.5

11.7

7.8

1

NA / NA

4

NO

MONITORED

FULL

22240001

6

pH

15 / 5

7.7

8.7

8.3

0

NA / NA

4

NO

MONITORED

FULL

22240001

6

Temperature

15 / 5

16.1

28.8

23.2

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

22240001

6

4

0.350226004

23.95%

0.097490221

4.08%

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

22240001

6

Ammonia

15 / 5

0.452

0.09

0.04

0 / 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)

1319

fillet

2024

channel catfish

3

43.5

0.042

<0.05

<0.0246

Support Level

Full

Monitoring and Methods
Assessment Key Dates
5/27/2020
Monitoring Start
9/3/2024
Monitoring End
10/11/2024
Fish Tissue Monitoring
Methods
200
Physical/Chemical Monitoring
260
Fish tissue analysis
340
Primary producer surveys (phytoplankton/periphyton/macrophyton)