DRAFT 2026 assessment for North Fork Yellow River

North Fork Yellow River IA 01-YEL-448

mouth (S13 T96N R7W Winneshiek Co.) to confluence with unnamed tributary in S3 T96N R7W Winneshiek Co.

This is a DRAFT assessment

Draft assessments may change without notice

2026
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

Overall IR

5 - Water is impaired or threatened and a TMDL is needed.

Trend

Stable

Current Phase

Public Comment

Created

10/27/2025 3:11:24 PM by

Updated

12/22/2025 1:27:27 PM by

Use Support

Class A1

Presumptive Use

Recreation - Primary contact

Not Supported

Bacteria: Indicator Bacteria- E. coli

Support Level

Not Supported

Impairment Code

4a - Pollutant-caused impairment. TMDL has been completed.

Cause Magnitude

High

303(d) Listing Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2008

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Watershed project monitoring

Class BWW2

Aquatic Life - Warm Water Type 2

Not Supported

Organic Enrichment: Low Dissolved Oxygen

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Moderate

303(d) Listing Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2008

Impairment Rationale

Significantly > 10% of samples fail to meet criterion

Data Source

Watershed project monitoring

TMDL Priority

Tier IV

303(d) Delistings for this Cycle

No delistings for this assessment cycle.

Documentation

Assessment Summary

The presumptive Class A1 use remains assessed as “not supported” due to levels of indicator bacteria (E. coli) that exceeded state water quality criteria. The Class BWW2 use remains assessed as "not supported" due to violations of criteria for dissolved oxygen. However, the most recent dissolved oxygen monitoring results indicate full support (too few samples). Note: A TMDL for the bacteria impairment for streams in the Yellow River basin was prepared by Iowa DNR in 2012 and was approved by U.S. EPA in February 2013. Due to completion of the TMDL, the Integrated Report category for the Class A1 recreational use was changed from 5p (impaired; TMDL needed) to 4a (impaired; TMDL approved). Because not all impairments identified for this assessment segment are covered by the TMDL (aquatic life use impairment due to low dissolved oxygen), this segment remains in Category 5a of Iowa's Integrated Report (impaired and TMDL required).

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2014	15960034	North Fork Yellow River at 111th Ave	Site 1
Iowa DNR	6	WQ	CY 2024	15960001	North Fork at Maple Valley Rd.

Presumptive Class A1 - Indicator Bacteria: 2014

Site ID	Data Source ID	# Samples / # Years	2014 Geometric Mean	Annual Geometric Mean Violation	# Violations	% Violations	Significantly >10% Violations	Assessment Type	Support Level
15960034	6	20 / 1	5621	Yes	19	95%	Yes	Evaluated	Not

Presumptive 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
15960001	6	6 / 1	7.96	8.44	8.28	0	3	NO	EVALUATED	FULL

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
15960001	6	Dissolved Oxygen	6 / 1	9.21	13.87	11.18	0	NA / NA	3	NO	EVALUATED	FULL
15960001	6	pH	6 / 1	7.96	8.44	8.28	0	NA / NA	3	NO	EVALUATED	FULL
15960001	6	Temperature	6 / 1	3.41	23.24	15.13	0	NA / NA	3	NO	EVALUATED	FULL

Monitoring and Methods

Assessment Key Dates

4/2/2024

Monitoring Start

9/4/2024

Monitoring End

4/22/2014

Monitoring Start

10/8/2014

Monitoring End

2/25/2013

TMDL Completed

Methods

150

Monitoring data more than 5 years old

200

Physical/Chemical Monitoring

420

Indicator bacteria monitoring