Iowa River IA 02-IOW-628

from Burlington St. dam in Iowa City (Johnson Co.) to Coralville Reservoir dam (Johnson 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: Declining
Trend Comment: New Class C nitrate impairment.
Created: 10/27/2025 3:09:36 PM
Updated: 1/15/2026 10:36:35 AM

Use Support

Class A1

Recreation - Primary contact

Fully Supported

Class BWW1

Aquatic Life - Warm Water Type 1

WINOFI

Biological: low aquatic macroinvertebrate IBI

Support Level

Further Investigation Needed

Impairment Code

3b-u - Use potentially biologically impaired based on uncalibrated IBI metrics.

Cause Magnitude

Moderate

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

Low

Cycle Added

2008

Impairment Rationale

Potential Impairment

Data Source

Biological monitoring: Iowa DNR WQMA

Class C

Drinking Water -

Not Supported

Nutrients: Nitrogen

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Slight

Status

New

Source

Unknown: Source Unknown

Source Confidence

Low

Cycle Added

2026

Impairment Rationale

Significantly > 10% of samples fail to meet criterion

Data Source

Ambient monitoring: municipal water supply

TMDL Priority

Tier I

Class HH

Human Health -

Fully Supported

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 use was assessed as "fully supported" based on indicator bacteria (E. coli) and pH monitoring data. The Class BWW1 use was assessed as "WINOFI" based on biological sampling data. The Class C (drinking water) use was assessed as "not supported" based on violations of the Class C criterion for nitrate. The Class HH (fish consumption) use remains assessed as "fully supported" based on fish tissue sampling data. Note: A TMDL for indicator bacteria in this segment of Iowa River approved by EPA in June 2007. Additionally, 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.

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
USACE	12	WQ	CY 2022-2024	2222222	Iowa River (Downstream Coralville Reservoir)
PWS	27	WQ	CY 2022-2024	99990175	Iowa River	University of Iowa
PWS	27	WQ	CY 2022-2024	99990176	Iowa River	Iowa City Water Department
Iowa DNR	6	BIO	See Below	941	Iowa River	Iowa City - US1
Iowa DNR	6	FT	See Below	1125	Iowa River at Iowa City

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

2222222

9/8/10

2 / 3

0 / 3

1 / 3

MONITORED

FULL

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
2222222	12	60 / 3	7.61	8.81	8.07	0	10	NO	MONITORED	FULL
99990175	27	1096 / 3	7.39	8.96	8.19	0	123	NO	MONITORED	FULL
99990176	27	75 / 3	7.95	9.03	8.29	1	12	NO	MONITORED	FULL

Class BWW1 - 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
2222222	12	Dissolved Oxygen	60 / 3	4.64	15.35	9.71	1	NA / NA	10	NO	MONITORED	FULL
2222222	12	pH	60 / 3	7.61	8.81	8.07	0	NA / NA	10	NO	MONITORED	FULL
99990175	27	pH	1096 / 3	7.39	8.96	8.19	0	NA / NA	123	NO	MONITORED	FULL
99990176	27	pH	75 / 3	7.95	9.03	8.29	1	NA / NA	12	NO	MONITORED	FULL
2222222	12	Temperature	60 / 3	1.2	27.5	15.8	0	NA / NA	10	NO	MONITORED	FULL
99990175	27	Temperature	1094 / 3	1.1	29.9	14.7	0	NA / NA	123	NO	MONITORED	FULL
99990176	27	Temperature	76 / 3	0	29	15	0	NA / NA	12	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
2222222	12	Ammonia	60 / 3	0.83	0.19	0.16	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	47f BMIBI BIT	BMIBI Pass/Fail
941	10/10/14	3158	47f	MS	Floating Art Sub	38	Fair	51	Fail

Overall:

Community	Assessment Type	Assessment Result	Support Level	IR Category	Reason
Benthic Macroinvertebrates	Evaluated	Fail (0/1)	WINOFI		Assessment was evaluated because the drainage area of
Overall	Evaluated	Fail	WINOFI	3bu	the sample site was greater than the calibrated range.

Class C - Binomial Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Minimum Value	Maximum Value	Mean Value	Median Value	# Violations	Violates Significantly >10% Rule?	Assessment Type	Support Level
2222222	12	Inorganic nitrogen (nitrate and nitrite)	58 / 3	0.2	15.1	3.7	2.2	6	NO	MONITORED	FULL
99990175	27	Nitrate	1096 / 3	0.1	16.6	3.3	2.2	33	NO	MONITORED	FULL
99990176	27	Nitrate	165 / 3	0.09	18	4.68	2.98	27	YES	MONITORED	NOT
2222222	12	pH	60 / 3	7.61	8.81	8.07	8.06	0	NO	MONITORED	FULL
99990175	27	pH	1096 / 3	7.39	8.96	8.19	8.2	0	NO	MONITORED	FULL
99990176	27	pH	75 / 3	7.95	9.03	8.29	8.26	1	NO	MONITORED	FULL

Class C - Toxic Parameters:

Site ID	Data Source ID	Parameter Name	# Samples per Year (2022)	2022 Mean	# Non-Detects per Year (2022)	Support Level per Year (2022)	Assessment Type	Support Level
99990176	27	Alachlor	12	0	12	Full	Mon	Full
99990176	27	Atrazine	18	0.63	15	Full	Mon	Full
99990176	27	Simazine	12	0	12	Full	Mon	Full

Class C - Iowa Drinking Water Compliance Report:

Compliance monitoring required by the Iowa DNR Water Supply Operations and Engineering Sections did not show violations of finished water caused by source water at the Iowa City Water Department or the University of Iowa Water System facilities during the 2022-24 monitoring period. The results of compliance monitoring as reported in annual compliance reports are available at the following location at the Iowa DNR’s home page:https://www.iowadnr.gov/Environmental-Protection/Water-Quality/Water-Supply-Engineering/Annual-Compliance-Report.

Class HH - Fish Tissue Sampling:

Site ID	Biopart	Year	Species	# in sample / # of samples	Avg Length (cm)	(Avg) Hg (ppm)	Chlordane (ppm)	Sum PCBs (ppm)
1125	fillet	2015	common carp	5	48.8	0.09	0.02	0.06
1125	tissue plug	2015	white bass	5	35.6	0.05
Support Level	Full

Monitoring and Methods

Assessment Key Dates

1/1/2022

Monitoring Start

12/31/2024

Monitoring End

10/10/2014

Biological Monitoring

8/15/2015

Fish Tissue Monitoring

6/1/2007

TMDL Completed

3/9/2018

TMDL Completed

Methods

150

Monitoring data more than 5 years old

200

Physical/Chemical Monitoring

260

Fish tissue analysis

275

Drinking water compliance reports

315

Regional reference site approach

320

Benthic macroinvertebrate surveys

420

Indicator bacteria monitoring