Walnut Creek IA 04-RAC-1120

mouth (S13 T78 R25W Polk Co.) to Interstate 35/80 in S33 T79N R25W Polk 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: 5 - Water is impaired or threatened and a TMDL is needed.
Trend: Unknown
Created: 11/1/2023 8:13:07 AM
Updated: 4/19/2024 10:24:46 AM

Use Support

Class A1

Recreation - Primary contact

Not Supported

Bacteria: Indicator Bacteria- E. coli

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Moderate

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2010

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Volunteer monitoring

TMDL Priority

Tier II

Class BWW2

Aquatic Life - Warm Water Type 2

WINOFI

Fish Kill: Caused By Chlorine

Support Level

Further Investigation Needed

Impairment Code

3b - Use potentially impaired based on an evaluated assessment.

Cause Magnitude

High

Status

Continuing

Source

Spills/Dumping: Accidental release/spill

Source Confidence

High

Cycle Added

2022

Impairment Rationale

Pollutant-caused fish kill

Data Source

Fish kill investigation: Iowa DNR

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 use was assessed as “not supported” based on levels of indicator bacteria (E. coli) that exceeded state water quality criteria. The Class BWW2 use was assessed (evaluated) as “WINOFI” based on the results of a fish kill investigation. The Class A1 use of this segment resided in Category 4a from 2010-2022; however, the 2008 Raccoon River TMDL did not include this segment.

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
IASNAPST	4	WQ	CY 2014-2016	977111	Walnut Creek - Site WC2	Polk County Snapshot
IASNAPST	4	WQ	CY 2014-2016	977113	Walnut Creek - Site WC4	Polk County Snapshot
IASNAPST	4	WQ	CY 2014-2016	977115	Walnut Creek - Site WC6	Polk County Snapshot

Class A1 - Indicator Bacteria: 2014 - 2016

Site ID	Data Source ID	# Samples / # Years	2014 Geometric Mean	2015 Geometric Mean	2016 Geometric Mean	Annual Geometric Mean Violation	# Violations	% Violations	Significantly >10% Violations	Assessment Type	Support Level
977111	4	6 / 3	192	322	173	Yes	3	50%	Yes	Evaluated	Not
977113	4	6 / 3	124	401	249	Yes	4	67%	Yes	Evaluated	Not
977115	4	6 / 3	177	401	228	Yes	4	67%	Yes	Evaluated	Not

Class BWW2 - Fish kill Assessment:

The Class BWW2 aquatic life use assessment based on the 2019 fish kill placed this segment in Category 3b. This assessment was “evaluated” because there was a single fish kill on this segment in the last five years. Segments assessed using “evaluated” assessments are placed in Category 3b and are added to the state list of Waters In Need Of Further Investigation (WINOFI). If no additional fish kills are reported in this segment for a 5-year period (2024), the Category will be changed from 3b to 3a (not assessed).

Details about the 2019 fish kill can be found here: https://programs.iowadnr.gov/fishkill/Events/974

Monitoring and Methods

Assessment Key Dates

5/7/2014

Monitoring Start

10/4/2016

Monitoring End

7/29/2019

Fish Kill

Methods

120

Surveys of fish and game biologists/other professionals

140

Incidence of spills and/or fish kills

150

Monitoring data more than 5 years old

420

Indicator bacteria monitoring