North Skunk River IA 03-NSK-863

from confluence with Sugar Cr. (S20 T78N R16W Poweshiek Co.) to confluence with Snipe Cr. in S22 T81N R19W Jasper Co.

Open Data Collection Period Modal

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.

Open Segment Map
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Cycle: 2024
Release Status: Final
Overall IR: 4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
Trend: Unknown
Created: 11/1/2023 8:12:52 AM
Updated: 2/5/2024 8:35:33 AM

Use Support

Class A1

Presumptive Use

Recreation - Primary contact

Not Assessed

Class BWW2

Aquatic Life - Warm Water Type 2

Not Supported

Habitat Alterations: Fish Habitat Degradation

Support Level

Not Supported

Impairment Code

4c - Non-pollutant caused impairment. No TMDL needed.

Cause Magnitude

Moderate

Status

Continuing

Source

Hydromodification

Source Confidence

N/A

Cycle Added

2004

Impairment Rationale

Low Biotic Index

Data Source

Biological monitoring: Iowa DNR WQMA

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class BWW2 use was assessed as "not supported” based on biological and habitat sampling data. This segment remains in Category 4c of Iowa's Integrated Report due to an impairment caused by a non-pollutant stressor (habitat alterations). 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	BIO	See Below	234	North Skunk River	Kellogg City Park – Site #3
Iowa DNR	6	BIO	See Below	235	North Skunk River	Newton – Site #4
Iowa DNR	6	BIO	See Below	236	North Skunk River	Sully – Site #2
Iowa DNR	6	BIO	See Below	1057	North Skunk River	SE of Kellogg – NS002

Presumptive Class A1 - No Data

Class BWW2 - Biological Sampling:

Fish:

BioNet Site ID	Date	Drainage Area (mi2)	Ecoregion	Major Drainage	Riffle Stream?	FIBI score	FIBI Class	47f FIBI BIT	FIBI Pass/Fail
1057	8/1/02	170	47f	MS	NA	24	Poor	36	Fail
235	8/9/01	115	47f	MS	NA	16	Poor	36	Fail
234	8/8/01	168	47f	MS	NA	19	Poor	36	Fail
236	8/7/01	243	47f	MS	NA	17	Poor	36	Fail

Overall:

Community	Assessment Type	Assessment Result	Support Level	IR Category	Reason
Fish	Evaluated	Fail (0/4)	Not		Assessment was evaluated because it included
Overall	Evaluated	Fail	Not	4c	samples not collected in a recent five-year period.

Class BWW2 – Habitat Index Evaluation:

For North Skunk River, the observed FIBI scores were moderately less than the EFHI-predicted FIBI scores. When the EFHI-predicted FIBI score-observed FIBI score difference is

+8 to -5 points, water quality and/or other factors besides physical habitat do not limit the stream’s ability to meet the FIBI BIT. The FIBI-EFHI differences at North Skunk River

were larger than the acceptable limit (-15 avg. vs -5); however, DNR still believes category 4c is the appropriate category for this segment. The fact that EFHI levels are below the

FIBI BIT is an indication that North Skunk River will have difficulty meeting the FIBI BIT because of habitat conditions in this segment. The 2006 IR indicated that habitat alterations

caused by agriculture, channelization, and hydromodification was the cause of the lower FIBI scores.

BioNet Site ID	Sample Date	FIBI Score	47f FIBI BIT	EFHI Score	FIBI-BIT Difference	FIBI-EFHI Difference	EFHI-BIT Difference
235	8/9/01	16	36	31	-20	-15	-5
234	8/8/01	19	36	33	-17	-14	-3
236	8/7/01	17	36	33	-19	-16	-3

Monitoring and Methods

Assessment Key Dates

8/7/2001

Biological Monitoring

8/8/2001

Biological Monitoring

8/9/2001

Biological Monitoring

8/1/2002

Biological Monitoring

Methods

150

Monitoring data more than 5 years old

315

Regional reference site approach

330

Fish surveys

380

Quantitative physical habitat assessment