South Fork Iowa River IA 02-IOW-750

from confluence with unnamed tributary in E 1/2 S11 T88N R22W Hardin Co. to confluence with unnamed tributary in NE 1/4 S32 T89N R22W Hardin 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: 12/8/2023 2:04:30 PM
Updated: 12/8/2023 2:07:05 PM

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

Slight

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2010

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Ambient monitoring: USDA/National Lab for Ag. and Environment

Class BWW2

Aquatic Life - Warm Water Type 2

Not Assessed

Impairment Delistings

Cycle Added	Class	Cause	Data Source	Rationale
2014	Class BWW2	Fish Kill: Caused By Silage Runoff	Biological monitoring: Iowa DNR fish kill follow-up	New data: recovery of fish community from pollutant-caused fish kill

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 was "not assessed" based on biological sampling data collected in 2022 that showed recovery of the fish community in this segment from the fish kill. Based on the 2022 fish sampling data, the 5b fish kill impairment was de-listed. Note: A TMDL covering the bacteria impairments for all segments, with the segment code prefix "IA 02-IOW" in the Iowa River Basin, was approved by EPA in 2018. Due to the completion of the TMDL, the IR category for the Class A1 use was changed from 5p (impaired; TMDL needed) to 4a (impaired; TMDL approved).

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
NLAE	20	WQ	CY 2010-2012	SF400	South Fork Iowa River	2 miles NNE of Buckeye

Presumptive Class A1 - Indicator Bacteria:

Site ID	Data Source ID	# Samples / # Years	2010 Geometric Mean	2011 Geometric Mean	2012 Geometric Mean	Annual Geometric Mean Violation	# Violations	% Violations	Significantly >10% Violations	Assessment Type	Support Level
SF400	20	23 / 3	304	361	344	Yes	15	65%	Yes	Evaluated	Not

Class BWW2 – Fish kill Assessment:

BioNet Site ID	Date	Drainage Area (mi2)	Ecoregion	Major Drainage/ Thermal	Fish per mile	47b REMAP 25 % fish per mile	>47b REMAP 25 % fish per mile?	2024 IR 47b expected fish taxa	Fish Taxa Present % (>50% to pass)
1397	08/11/22	92.6	47b	MS/WW	3105	1362	Yes (Pass)	11/12	91.6% (Pass)
The Class BWW2 use previously resided in Category 5b based on a fish kill that occurred in 2011. This segment’s fish community was sampled in 2022 as part of the DNR fish kill follow-up sampling program. The results from this follow-up sampling and comparison to ecoregion averages suggest that the fish community of this segment is similar to non-fish kill impacted streams. Based on the fish kill follow-up sampling results, the Category for the fish kill assessment was changed from 5b to 3a (not assessed).

Details about the 2011 fish kill can be found here:https://programs.iowadnr.gov/fishkill/Events/843

Monitoring and Methods

Assessment Key Dates

9/29/2011

Fish Kill

3/12/2010

Monitoring Start

7/7/2012

Monitoring End

3/9/2018

TMDL Completed

8/11/2022

Biological Monitoring

Methods

140

Incidence of spills and/or fish kills

150

Monitoring data more than 5 years old

200

Physical/Chemical Monitoring

330

Fish surveys

420

Indicator bacteria monitoring