Iowa DNR
ADBNet

Water Quality Assessments

Impaired Waters List

South Skunk River IA 03-SSK-934

from the Ames Water Works dam in River Valley Park at Ames (S36 T84N R24W Story Co.) to the Co. Rd. at north line of S6 T85 R23W Story Co (approximately 1 mile NNE of Story City)

Assessment Cycle
2022
Release Status
Final
Cycle Period
2018 - 2020
Overall IR Category
5 - Water is impaired or threatened and a TMDL is needed.
Trend
Unknown
Created
12/22/2021 11:54:26 AM
Updated
1/7/2022 11:36:54 AM
Assessment conducted in accordance with Iowa's 2022 IR methodology
Use Support
Class A1
Not Supported
Bacteria: Indicator Bacteria- E. coli
Support Level
Not Supported
Impairment Code
5a - Pollutant-caused impairment. TMDL needed.
Cause Magnitude
Slight
Status
Continuing
Source
Unknown: Source Unknown
Source Confidence
N/A
Cycle Added
2004
Impairment Rationale
Geometric mean criterion exceeded
Data Source
Ambient monitoring: Iowa DNR-rivers
TMDL Priority
Tier III
Class BWW1
Not Supported
Biological: low fish & invert IBIs- cause unknown
Support Level
Not Supported
Impairment Code
5b-v - Biological - verified
Cause Magnitude
Slight
Status
Continuing
Source
Unknown: Source Unknown
Source Confidence
Low
Cycle Added
2016
Impairment Rationale
Low Biotic Index
Data Source
Biological monitoring: Iowa DNR WQMA
TMDL Priority
Tier IV
Class HH
Not Assessed
Impairment Delistings
No delistings for this assessment cycle.
Documentation
Assessment Summary

The Class A1 use was assessed as “not supported” due to levels of indicator bacteria that violated state water quality criteria. The Class BWW1 use was assessed as "not supported" based on biological sampling data. All other designated uses were "not assessed."

Assessment Explanation

Data Sources:

Data Source

Data Source ID

Data Type

Data Age

Site ID

Site Name

Site Description

Iowa DNR

6

WQ

CY 2012-2014

10850003

South Skunk River Upstream of Ames (US1)

Iowa DNR

6

BIO

See Below

38

South Skunk River

Ames

Iowa DNR

6

BIO

See Below

972

South Skunk River

Ames – US1


Class A1 - Indicator Bacteria:

Site ID

Data Source ID

# Samples / # Years

2012 Geometric Mean

2013 Geometric Mean

2014 Geometric Mean

Annual Geometric Mean Violation

# Violations

% Violations

Significantly >10% Violations

Assessment Type

Support Level

10850003

6

22 / 3

46

94

223

Yes

7

32%

Yes

Evaluated

Not


Class A - pH:

Site ID

Data Source ID

# Samples / # Years

Maximum Value

Mean Value

Median Value

# Violations

% Violations

Significantly >10% Violations

Assessment Type

Support Level

10850003

6

33 / 3

8.6

8.1

8.1

0

0%

No

Evaluated

Full


Class BWW1 - Conventional Parameters:

Site ID

Data Source ID

Parameter Name

# Samples / # Years

Maximum Value

Mean Value

Median Value

# Acute / Chronic Violations

% Acute/ Chronic Violations

Significantly >10% Violations

Assessment Type

Support Level

10850003

6

Ammonia

33 / 3

1.7

0.15

0.05

0 / 0

0% / 0%

No

Evaluated

Full

10850003

6

Chloride

33 / 3

100

43

35

0 / 0

0% / 0%

No

Evaluated

Full

10850003

6

Dissolved oxygen

33 / 3

16.2

10.7

10.2

NA / 0

NA / 0%

No

Evaluated

Full

10850003

6

pH

33 / 3

8.6

8.1

8.1

0 / NA

0% / NA

No

Evaluated

Full

10850003

6

Sulfate

33 / 3

110

46

41

0 / NA

0% / NA

No

Evaluated

Full

10850003

6

Temperature

33 / 3

27.5

12

12.4

0 / 0

0% / 0%

No

Evaluated

Full


Class BWW1 - Biological Sampling:

Benthic Macroinvertebrates:

BioNet Site ID

Date

Drainage Area (mi2)

Ecoregion

Major Drainage/Thermal

BM Sample Gear

BMIBI score

BMIBI Class

47b BMIBI BIT

BMIBI Pass/Fail

38

8/31/17

254

47b

MS/WW

Surb

58

Good

62

Fail

972

9/4/14

315

47b

MS/WW

Hess

53

Fair

62

Fail

972

9/4/14

315

47b

MS/WW

ArtSub

38

Fair

62

Fail

Fish:

BioNet Site ID

Date

Drainage Area (mi2)

Ecoregion

Major Drainage/Thermal

Riffle Stream?

FIBI score

FIBI Class

47b FIBI BIT

FIBI Pass/Fail

38

8/31/17

254

47b

MS/WW

No

70

Good

32

Pass

38

7/18/13

254

47b

MS/WW

No

13

Poor

32

Fail


Overall:

Community

Assessment Type

Assessment Result

Support Level

IR Category

Reason

Benthic Macroinvertebrates

Evaluated

Fail (0/3)

Not

Fish

Evaluated

Fail (1/2)

Not

Assessment was evaluated because it included samples

Overall

Evaluated

Fail

Not

5bv

not collected in the last five years.


Class BWW1 - Fish kill Assessment:

The Class BWW1 use previously resided in IR Category 3b based on the assessment developed for the 2011 fish kill. Because no additional fish kills were reported in this segment for at least 10 years post fish kill (2021), the IR Category for the fish kill assessment was changed from 3b to 3a (not assessed). DNR believes that any impact from the fish kill from which the impairment was based has likely dissipated.

Details about the 2011 fish kill can be found here: https://programs.iowadnr.gov/fishkill/Events/832.


Class HH - No Data

Monitoring and Methods
Assessment Key Dates
7/18/2013 Biological Monitoring
9/4/2014 Biological Monitoring
1/10/2012 Fixed Monitoring Start Date
9/4/2014 Fixed Monitoring End Date
8/31/2017 Biological Monitoring
Methods
150 Monitoring data more than 5 years old
315 Regional reference site approach
320 Benthic macroinvertebrate surveys
330 Fish surveys
420 Water column surveys (e.g. fecal coliform)
210 Fixed station physical/chemical monitoring (conventional pollutants only)