South River IA 04-LDM-1074

mouth (Warren Co.) to confluence with Squaw Cr. in S2 T75N R24W Warren 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: Stable
Created: 10/27/2025 3:09:45 PM
Updated: 11/24/2025 3:35:38 PM

Use Support

Class A1

Presumptive Use

Recreation - Primary contact

Not Supported

Bacteria: Indicator Bacteria- E. coli

Support Level

Not Supported

Impairment Code

5p - Impairment occurs on a waterbody with a presumptive A1 or B(WW1) use.

Cause Magnitude

Moderate

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2008

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Ambient monitoring: Iowa DNR-rivers

TMDL Priority

Tier III

Class BWW2

Aquatic Life - Warm Water Type 2

Not Supported

Biological: low aquatic macroinvertebrate IBI

Support Level

Not Supported

Impairment Code

5b-v - Biological - verified

Cause Magnitude

Moderate

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2022

Impairment Rationale

Low Biotic Index

Data Source

Biological monitoring: Iowa DNR WQMA

TMDL Priority

Tier IV

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The presumptive Class A1 use was assessed as "not supported" due to levels of indicator bacteria (E. coli) that violated state water quality criteria. The Class BWW2 use was assessed as "not supported” based on biological sampling data.

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2022-2024	10910003	South River near Ackworth
Iowa DNR	6	BIO	See Below	931	South River	Ackworth
Iowa DNR	6	BIO	See Below	1239	South River	Bank Swallow Bend – Ackworth (REMAP # 305)

Presumptive Class A1 - Indicator Bacteria:

Site ID

Data Source ID

# Samples per Year (2022/ 2023/2024)

2022 Geometric Mean

2023 Geometric Mean

2024 Geometric Mean

Violates Annual Geometric Mean?

# 2022 SSM violations / SSM Violations needed for impairment

# 2023 SSM violations / SSM Violations needed for impairment

# 2024 SSM violations / SSM Violations needed for impairment

Violates Annual SSM Significantly >10% Rule?

Assessment Type

Support Level

10910003

8/8/7

651

411

677

YES

6 / 3

5 / 3

YES

MONITORED

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
10910003	6	36 / 3	6.7	8.1	7.7	0	7	NO	MONITORED	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
10910003	6	Chloride	36 / 3	10	33	17	NA	0 / 0	7	NO	MONITORED	FULL
10910003	6	Dissolved Oxygen	36 / 3	6.9	14.7	9.8	0	NA / NA	7	NO	MONITORED	FULL
10910003	6	pH	36 / 3	6.7	8.1	7.7	0	NA / NA	7	NO	MONITORED	FULL
10910003	6	Sulfate	36 / 3	20	64	40	0	NA / NA	7	NO	MONITORED	FULL
10910003	6	Temperature	36 / 3	0	24.9	11	0	NA / NA	7	NO	MONITORED	FULL

Class BWW2 - Toxic Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Maximum Value	Mean Value	Median Value	# Acute / Chronic Violations	>1 Acute / Chronic Violation	Assessment Type	Support Level
10910003	6	Ammonia	36 / 3	0.21	0.05	0.02	0 / 0	NO	MONITORED	FULL
10910003	6	Cadmium	18 / 2	0.5	0.5	0.5	0 / 0	NO	MONITORED	FULL
10910003	6	Chromium	18 / 2	4	1.25	0.6	0 / 0	NO	MONITORED	FULL
10910003	6	Copper	18 / 2	8	3	2	0 / 0	NO	MONITORED	FULL
10910003	6	Lead	18 / 2	1	1	1	0 / 0	NO	MONITORED	FULL
10910003	6	Nickel	18 / 2	4.1	2.7	2.6	0 / 0	NO	MONITORED	FULL
10910003	6	Selenium	36 / 3	3	0.8	0.5	0 / 0	NO	MONITORED	FULL
10910003	6	Silver	18 / 2	1	1	1	0 / 0	NO	MONITORED	FULL
10910003	6	Zinc	18 / 2	2.9	0.9	0.5	0 / 0	NO	MONITORED	FULL

Class BWW2 - Biological Sampling:

Benthic Macroinvertebrates:

Site ID	Date	Drainage Area (mi2)	Ecoregion	Major Drainage	BM Sample Gear	BMIBI score	BMIBI Class	47f BMIBI BIT	BMIBI Pass/Fail
931	8/10/22	474.0	47f	MS	Floating Art Sub	23	Poor	51	Fail
1239	9/23/20	464.0	47f	MS	Surber	30	Poor	51	Fail

Fish:

Site ID	Date	Drainage Area (mi2)	Ecoregion	Major Drainage	Riffle Stream?	FIBI score	FIBI Class	47f FIBI BIT	FIBI Pass/Fail
1239	9/23/20	464.0	47f	MS	NA	47	Fair	36	Pass

Overall:

Community	Assessment Type	Assessment Result	Support Level	IR Category	Reason
Benthic Macroinvertebrates	Monitored	Fail (0/2)	Not
Fish	Evaluated	Pass (1/1)	Full		Assessment was monitored because the samples used to complete
Overall	Monitored	Fail	Not	5bv	the (BMIBI) assessment were collected in a recent five-year period.

Monitoring and Methods

Assessment Key Dates

1/4/2022

Monitoring Start

12/10/2024

Monitoring End

9/23/2020

Biological Monitoring

8/10/2022

Biological Monitoring

Methods

200

Physical/Chemical Monitoring

315

Regional reference site approach

320

Benthic macroinvertebrate surveys

330

Fish surveys

420

Indicator bacteria monitoring