Iowa River IA 02-IOW-627

from confluence with English R. (Washington Co.) to Burlington Street Dam in Iowa City (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: 4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
Trend: Stable
Created: 10/27/2025 3:09:36 PM
Updated: 12/29/2025 8:53:08 AM

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

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2010

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Ambient monitoring: Iowa DNR-rivers

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

2014

Impairment Rationale

Potential Impairment

Data Source

Biological monitoring: Iowa DNR WQMA

Class HH

Human Health -

Fully Supported

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 use was assessed as "not supported" based on historic indicator bacteria monitoring data. The Class BWW1 use was assessed as “WINOFI” based on biological sampling data. The Class HH use was assessed as "fully supported" based on fish tissue sampling data. 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 5a (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
Iowa DNR	6	WQ	CY 2010-2012	10520003	Iowa River Downstream of Iowa City (DS1)	County Road F62 bridge E of Hills
Iowa DNR	6	BIO	See Below	940	Iowa River	Iowa City – DS1
Iowa DNR	6	FT	See Below	1370	Iowa River	Below Coralville Dam

Class A1 - Indicator Bacteria: 2010-2012

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
10520003	6	24 / 3	117	132	75	Yes	4	17%	No	Evaluated	Not

Class BWW1 - Biological Sampling:

Benthic Macroinvertebrates:

BioNet Site ID	Date	Drainage Area (mi2)	Ecoregion	Major Drainage	BM Sample Gear	BMIBI score	BMIBI Class	72d BMIBI BIT	BMIBI Pass/Fail
942	9/18/13	3323	72d	MS	Art Sub	15	Poor	51	Fail
942	9/14/12	3323	72d	MS	Art Sub	30	Poor	51	Fail

Overall:

Community	Assessment Type	Assessment Result	Support Level	IR Category	Reason
Benthic Macroinvertebrates	Evaluated	Fail (0/2)	WINOFI		Assessment was evaluated because the drainage area of
Overall	Evaluated	Fail	WINOFI	3bu	the sample site was greater than the calibrated range.

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)
1370	tissue plug	2021	channel catfish	5	45.3	0.107
1370	tissue plug	2021	smallmouth bass	9	26.4	0.124
Support Level	Full

Monitoring and Methods

Assessment Key Dates

1/5/2010

Monitoring Start

12/4/2012

Monitoring End

9/18/2013

Biological Monitoring

3/9/2018

TMDL Completed

7/1/2021

Fish Tissue Monitoring

7/6/2021

Fish Tissue Monitoring

9/14/2012

Biological Monitoring

Methods

150

Monitoring data more than 5 years old

260

Fish tissue analysis

315

Regional reference site approach

320

Benthic macroinvertebrate surveys

420

Indicator bacteria monitoring