Walnut Creek IA 04-RAC-1120

mouth (S13 T78 R25W Polk Co.) to Interstate 35/80 in S33 T79N R25W Polk Co.

This is a DRAFT assessment

Draft assessments may change without notice

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 2022 - 2024
Stream/River Water Quality Data	CY 2022 - 2024
Lake Water Quality Data	CY 2020 - 2024
Biological Sampling Data	CY 2020 - 2024*
Fish Kill Data	CY 2020 - 2024
Fish Tissue Sampling Data	CY 2020 - 2024
Continuous Dissolved Oxygen Sampling Data	CY 2020 - 2024
*Biological sites sampled in both 2019 and 2023 were also assessed.

Open Segment Map
View 2026 assessment summary page

Cycle: 2026
Current Phase: Public Comment
Overall IR: 5 - Water is impaired or threatened and a TMDL is needed.
Trend: Unknown
Created: 10/27/2025 3:09:54 PM
Updated: 1/13/2026 11:16:27 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

Fully Supported

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 use remains assessed as “not supported” based on historic levels of indicator bacteria (E. coli) that exceeded state water quality criteria. The Class BWW2 use was assessed as “fully supported” based on water quality data. 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
PCCB	29	WQ	CY 2022-2024	99990306	Walnut Creek at NW 114thSt
PCCB	29	WQ	CY 2022-2024	99990307	Walnut Creek at 22nd St
PCCB	29	WQ	CY 2022-2024	99990308	Walnut Creek at Grand Ave
PCCB	29	WQ	CY 2022-2024	99990231	Walnut Creek at N Valley Dr
PCCB	29	WQ	CY 2022-2024	99990232	Walnut Creekat Interstate 235
PCCB	29	WQ	CY 2022-2024	99990248	Walnut Creek at NW 100th St

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 - 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
99990306	29	Chloride	5 / 2	44.28	78.87	55.17	NA	0 / 0	2	NO	EVALUATED	FULL
99990307	29	Chloride	6 / 2	34.72	86.39	62.7	NA	0 / 0	3	NO	EVALUATED	FULL
99990308	29	Chloride	6 / 3	16.14	122.49	73.85	NA	0 / 0	3	NO	EVALUATED	FULL
99990306	29	Sulfate	5 / 2	26.31	49.15	38.08	0	NA / NA	2	NO	EVALUATED	FULL
99990307	29	Sulfate	6 / 2	15.32	42.61	31.99	0	NA / NA	3	NO	EVALUATED	FULL
99990308	29	Sulfate	6 / 3	8.3	51	34.3	0	NA / NA	3	NO	EVALUATED	FULL
99990231	29	Temperature	58 / 3	-2.77778	35.5556	15.077	2	NA / NA	10	NO	MONITORED	FULL
99990232	29	Temperature	62 / 3	-2.22222	34.4444	14.579	1	NA / NA	10	NO	MONITORED	FULL
99990248	29	Temperature	55 / 3	-0.55556	31.1111	16.192	0	NA / NA	9	NO	MONITORED	FULL
99990306	29	Temperature	5 / 3	16.6667	23.3333	20.222	0	NA / NA	2	NO	EVALUATED	FULL
99990307	29	Temperature	5 / 3	17.2222	22.7778	19.333	0	NA / NA	2	NO	EVALUATED	FULL
99990308	29	Temperature	5 / 3	15	20.5556	18.333	0	NA / NA	2	NO	EVALUATED	FULL

Monitoring and Methods

Assessment Key Dates

5/7/2014

Monitoring Start

10/4/2016

Monitoring End

1/8/2022

Monitoring Start

12/15/2024

Monitoring End

Methods

150

Monitoring data more than 5 years old

200

Physical/Chemical Monitoring

420

Indicator bacteria monitoring

860

Other Agencies/Organizations provided monitoring data