DRAFT 2026 assessment for Volga River

Volga River IA 01-VOL-289

mouth (S36 T92N R4W Clayton Co.) to confluence with Cox Cr. in S21 T92N R5W Clayton 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

4 - Water is impaired or threatened and a TMDL has been completed or is not needed.

Trend

Stable

Current Phase

Public Comment

Created

10/27/2025 3:08:48 PM by

Updated

11/17/2025 9:38:52 AM by

Use Support

Class A1

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

303(d) Listing Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

1998

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Ambient monitoring: Iowa DNR-rivers

Class BWW1

Aquatic Life - Warm Water Type 1

Fully Supported

Class HH

Human Health -

Fully Supported

303(d) Delistings for this Cycle

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 use was assessed as "not supported" due to levels of indicator bacteria (E. coli) that exceeded Iowa’s water quality standards. The Class BWW1 use was assessed as "fully supported" based on biological sampling data and on water quality monitoring data. The Class HH use was assessed as "fully supported" based on water quality monitoring data. Note: A TMDL for pathogen indicators in this segment of the Volga River was prepared by DNR and approved by EPA in 2006. Because the primary Section 303(d) impairment identified (indicator bacteria) was addressed by the TMDL, the Class A1 use was remains IR Category 4a (impaired; TMDL approved).

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	10220002	Volga River near Elkport
Iowa DNR	6	BIO	See Below	283	Volga River	Elkport

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

10220002

8/8/8

278

103

177

YES

3 / 3

1 / 3

2 / 3

YES

MONITORED

NOT

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
10220002	6	35 / 3	7.8	8.5	8.2	0	7	NO	MONITORED	FULL

Class BWW1 - Conventional 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
10220002	6	Chloride	36 / 3	12	29	16	NA	0 / 0	7	NO	MONITORED	FULL
10220002	6	Dissolved Oxygen	36 / 3	7.8	14.3	11.1	0	NA / NA	7	NO	MONITORED	FULL
10220002	6	pH	35 / 3	7.8	8.5	8.2	0	NA / NA	7	NO	MONITORED	FULL
10220002	6	Sulfate	36 / 3	12	25	19	0	NA / NA	7	NO	MONITORED	FULL
10220002	6	Temperature	36 / 3	0	25.7	12.4	0	NA / NA	7	NO	MONITORED	FULL

Class BWW1 - 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
10220002	6	Ammonia	35 / 3	0.23	0.04	0.02	0 / 0	NO	MONITORED	FULL
10220002	6	Cadmium	18 / 2	0.5	0.5	0.5	0 / 0	NO	MONITORED	FULL
10220002	6	Chromium	18 / 2	12	1.7	0.9	0 / 1	NO	MONITORED	FULL
10220002	6	Copper	18 / 2	2.9	0.9	0.5	0 / 0	NO	MONITORED	FULL
10220002	6	Lead	18 / 2	1	1	1	0 / 0	NO	MONITORED	FULL
10220002	6	Nickel	18 / 2	1.4	0.8	0.8	0 / 0	NO	MONITORED	FULL
10220002	6	Selenium	36 / 3	1.1	0.5	0.5	0 / 0	NO	MONITORED	FULL
10220002	6	Silver	18 / 2	1	1	1	0 / 0	NO	MONITORED	FULL
10220002	6	Zinc	18 / 2	2.4	0.7	0.5	0 / 0	NO	MONITORED	FULL

Class BWW1 - Biological Sampling:

Benthic Macroinvertebrates:

Site ID	Date	Drainage Area (mi2)	Ecoregion	Major Drainage	BM Sample Gear	BMIBI score	BMIBI Class	52b BMIBI BIT	BMIBI Pass/Fail
283	8/12/24	403	52b	MS	Floating Art Sub	71	Good	61	Pass

Overall:

Community	Assessment Type	Assessment Result	Support Level	IR Category	Reason
Benthic Macroinvertebrates	Evaluated	Pass (1/1)	Full
Overall	Evaluated	Pass	Full	1	The assessment was evaluated because it was based on a single sample.

Class HH-F - Toxic Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Maximum Value	Mean Value	Median Value	Number of Non - Detects	Mean Value > Criterion or MCL	Assessment Type	Support Level
10220002	6	Copper	18 / 2	2.9	0.9	0.5	11	NO	MONITORED	FULL
Site ID	Data Source ID	Parameter Name	# Samples per Year (2022/ 2023/2024)	2022 Mean	2023 Mean	2024 Mean	# Non-Detects per Year (2022/ 2023/2024)	Support Level per Year (2022/ 2023/2024)	Assessment Type	Support Level
10220002	6	Selenium	12/12/12	0.542	0.5	0.55	11/12/11	FS/FS/FS	MONITORED	FULL

Monitoring and Methods

Assessment Key Dates

1/6/2022

Monitoring Start

8/12/2024

Biological Monitoring

7/1/2006

TMDL Completed

12/3/2024

Monitoring End

Methods

200

Physical/Chemical Monitoring

315

Regional reference site approach

320

Benthic macroinvertebrate surveys

420

Indicator bacteria monitoring