2020 Final assessment for Walnut Creek

Walnut Creek IA 03-SSK-953

mouth (S5 T82N R23W Story Co.) to confluence with unnamed tributary in SE 1/4 S34 T83N R24W Story Co.

Assessment Cycle

2020

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 2016 - 2018
Stream/River Water Quality Data	CY 2016 - 2018
Lake Water Quality Data	CY 2014 - 2018
Biological Sampling Data	CY 2014 - 2018*
Fish Kill Data	CY 2014 - 2018
Fish Tissue Sampling Data	CY 2014 - 2018
Continuous Dissolved Oxygen Sampling Data	CY 2014 - 2018
*Biological sites sampled in both 2013 and 2017 were also assessed.

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

Created: 9/9/2020 3:04:25 PM
Updated: 10/16/2020 10:50:29 AM

Assessment conducted in accordance with Iowa's 2020 IR methodology

Use Support

Class A1

Presumptive Use

Not Assessed

Class BWW2

Partially Supported

Biological: low fish IBI

Support Level

Partially Supported

Impairment Code

5b-t - Biological - tentative

Cause Magnitude

Moderate

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

Low

Cycle Added

2004

Impairment Rationale

Low Biotic Index

Data Source

Biological monitoring: Iowa DNR WQMA

TMDL Priority

Tier IV

General Use

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class BWW2 use remains assessed as "partially supported" based on biological sampling data. All other designated uses were "not assessed".

Assessment Explanation

Sources of Data:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	BIO	See Below	210	Walnut Creek	Ames
Iowa DNR	6	BIO	See Below	859	Walnut Creek	Huxley

Presumptive Class A1 - No Data

Class BWW2 - 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
859	8/22/11	18	47b	MS/WW	LowFlow ArtSub	48	Fair	62	Fail
210	7/19/11	13	47b	MS/WW	Surb	68	Good	62	Pass
210	7/17/07	13	47b	MS/WW	Hess	77	Excellent	62	Pass

Fish:

BioNet Site ID	Date	Drainage Area (mi2)	Ecoregion	Major Drainage/Thermal	Riffle Stream?	FIBI score	FIBI Class	47b FIBI BIT	FIBI Pass/ Fail
859	7/20/11	18	47b	MS/WW	No	17	Poor	32	Fail
210	7/19/11	13	47b	MS/WW	Yes	36	Fair	53	Fail
210	7/17/07	13	47b	MS/WW	Yes	29	Fair	53	Fail

Overall:

Community	Assessment Type	Assessment Result	Support Level	Earned IR Category	Actual IR Category	Reason
Benthic Macroinvertebrates	Evaluated	Pass (2/3)	Full
Fish	Evaluated	Fail (0/3)	Partial
Overall	Evaluated	Fail	Partial	3bc	5bt	Assessment is evaluated because it included samples not collected in the last five years.

Monitoring and Methods

Assessment Key Dates

7/17/2007	Biological Monitoring
7/19/2011	Biological Monitoring
7/20/2011	Biological Monitoring

Methods

150	Monitoring data more than 5 years old
315	Regional reference site approach
320	Benthic macroinvertebrate surveys
330	Fish surveys

Water Quality Assessments

Impaired Waters List

Walnut Creek IA 03-SSK-953

Assessment Summary

Assessment Explanation

Assessment Key Dates

Methods