2024 Pending assessment for Skunk River

Skunk River IA 03-SKU-889

mouth to confluence with Big Cr. southeast of Mt. Pleasant in S19 T70N R5W in Henry Co.

Assessment Cycle

2024

Release Status

Pending

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 2020 - 2022
Stream/River Water Quality Data	CY 2020 - 2022
Lake Water Quality Data	CY 2018 - 2022
Biological Sampling Data	CY 2018 - 2022*
Fish Kill Data	CY 2018 - 2022
Fish Tissue Sampling Data	CY 2018 - 2022
Continuous Dissolved Oxygen Sampling Data	CY 2018 - 2022
*Biological sites sampled in both 2017 and 2021 were also assessed.

Overall IR Category: 5 - Water is impaired or threatened and a TMDL is needed.
Trend: Unknown

Created: 11/1/2023 8:12:52 AM
Updated: 12/15/2023 1:39:13 PM

Assessment conducted in accordance with Iowa's 2024 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

2012

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Ambient monitoring: Iowa DNR-rivers

TMDL Priority

Tier III

Class BWW1

Fully Supported

Class HH

Fully Supported

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 (E. coli) that exceeded state water quality criteria. The Class BWW1 use was assessed as "fully supported" based on biological sampling data and water quality monitoring data. The Class HH use was assessed as "fully supported" based on fish tissue sampling data and water quality monitoring 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 2020-2022	10560002	Skunk River near Augusta
USGS	11	WQ	CY 2020-2020	5474000	Skunk River at Augusta, IA
Iowa DNR	6	BIO	See Below	943	Skunk River	Augusta
Iowa DNR	6	BIO	See Below	1300	Skunk River	New London (REMAP #382)
Iowa DNR	6	FT	See Below	1169	Skunk River	NE of Weaver

Class A1 - Indicator Bacteria:

Site ID

Data Source ID

# Samples per Year (2020/ 2021/2022)

2020 Geometric Mean

2021 Geometric Mean

2022 Geometric Mean

Violates Annual Geometric Mean?

# 2020 SSM violations / SSM Violations needed for impairment

# 2021 SSM violations / SSM Violations needed for impairment

# 2022 SSM violations / SSM Violations needed for impairment

Violates Annual SSM Significantly >10% Rule?

Assessment Type

Support Level

10560002

8/8/7

175

200

156

YES

4 / 3

2 / 3

1 / 3

YES

Mon

Not

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
10560002	6	36 / 3	7.3	8.6	8.2	0	7	NO	Mon	Full

Class BWW1 - 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
10560002	6	Chloride	36 / 3	11	44	25	NA	0 / 0	7	NO	Mon	Full
10560002	6	Dissolved Oxygen	36 / 3	7	18.1	10.6	0	NA / NA	7	NO	Mon	Full
10560002	6	pH	36 / 3	7.3	8.6	8.2	0	NA / NA	7	NO	Mon	Full
10560002	6	Sulfate	36 / 3	11	68	37	0	NA / NA	7	NO	Mon	Full
10560002	6	Temperature	36 / 3	0	29.3	12.7	0	NA / NA	7	NO	Mon	Full
5474000	11	Temperature	902 / 3	-4	32	15	0	NA / NA	103	NO	Mon	Full

Class BWW1 - 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
10560002	6	Ammonia	36 / 3	0.51	0.05	0.02	0 / 0	NO	Mon	Full
10560002	6	Cadmium	20 / 3	0.5	0.5	0.5	0 / 0	NO	Mon	Full
10560002	6	Chromium	20 / 3	3	0.91	0.52	0 / 0	NO	Mon	Full
10560002	6	Lead	20 / 3	1	0.9	1	0 / 0	NO	Mon	Full
10560002	6	Nickel	20 / 3	2.9	1.8	1.8	0 / 0	NO	Mon	Full
10560002	6	Selenium	18 / 2	2	0.9	0.5	0 / 0	NO	Mon	Full
10560002	6	Silver	20 / 3	1	0.902	1	0 / 0	NO	Mon	Full
10560002	6	Zinc	20 / 3	2.7	0.9	0.5	0 / 0	NO	Mon	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	40a BMIBI BIT	BMIBI Pass/Fail
1300	9/16/21	4230.0	40a	MS/WW	Floating ArtSub	56	Good	41	Pass
943	8/29/19	4303.0	40a	MS/WW	Hess	60	Good	41	Pass

Fish:

BioNet Site ID	Date	Drainage Area (mi2)	Ecoregion	Major Drainage/Thermal	Riffle Stream?	FIBI score	FIBI Class	40a FIBI BIT	FIBI Pass/Fail
1300	9/16/21	4230.0	40a	MS/WW	NA	40	Fair	33	Pass

Overall:

Community	Assessment Type	Assessment Result	Support Level	IR Category	Reason
Benthic Macroinvertebrates	Evaluated	Pass (2/2)	Full
Fish	Evaluated	Pass (1/1)	Full		Assessment was evaluated because the drainage area of the site
Overall	Evaluated	Pass	Full	1	used for the assessment was greater than the calibrated range.

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)
1169	whole	2016	common carp	5	59.3	0.08	0.05	0.06
Support Level	Full

Class HH-F - Toxic Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Maximum Value	Mean Value	Median Value	Number of Non - Detects	Mean Value > Criterion or MCL	Assessment Type	Support Level
10560002	6	Selenium	18 / 2	2	0.9	0.5	11	NO	Mon	Full

Monitoring and Methods

Assessment Key Dates

1/8/2020	Monitoring Start
12/16/2022	Monitoring End
8/29/2019	Biological Monitoring
9/14/2016	Fish Tissue Monitoring
9/16/2021	Biological Monitoring

Methods

200	Physical/Chemical Monitoring
315	Regional reference site approach
320	Benthic macroinvertebrate surveys
420	Indicator bacteria monitoring

Water Quality Assessments

Impaired Waters List

Skunk River IA 03-SKU-889

Assessment Summary

Assessment Explanation

Assessment Key Dates

Methods