2022 Final assessment for South Skunk River

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

Data Collection Period

For purposes of developing stream/river water quality assessments for integrated reporting, three years of water quality data are typically used for both conventional pollutant parameters (e.g., indicator bacteria) and the less frequently monitored toxic parameters (e.g., toxic metals). Since the 2004 IR cycle, DNR has used a three-year data gathering period for streams, rivers, and beaches. For most assessments, the use of three years of data increases the number of samples upon which the decision on use support is based and helps address the problem of weather-related year-to-year fluctuations in water quality.

Due to the lower sampling frequency in Iowa’s ambient lake, biological, fish kill, and fish tissue monitoring programs, five years of data are used for developing IR assessments and for identifying Section 303(d) listings.

Data Type	Data Timeframe
Beach Sampling Data	CY 2018 - 2020
Stream/River Water Quality Data	CY 2018 - 2020
Lake Water Quality Data	CY 2016 - 2020
Biological Sampling Data	CY 2016 - 2020*
Fish Kill Data	CY 2016 - 2020
Fish Tissue Sampling Data	CY 2016 - 2020
Continuous Dissolved Oxygen Sampling Data	CY 2016 - 2020
*Biological sites sampled in both 2015 and 2019 were also assessed.

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
210	Fixed station physical/chemical monitoring (conventional pollutants only)
315	Regional reference site approach
320	Benthic macroinvertebrate surveys
330	Fish surveys
420	Indicator bacteria monitoring

Water Quality Assessments

Impaired Waters List

South Skunk River IA 03-SSK-934

Assessment Summary

Assessment Explanation

Assessment Key Dates

Methods