Iowa River IA 02-IOW-621

mouth (Louisa Co.) to S. corporate limit of Wapello (S35 T74N R3W Louisa 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 2018 - 2020
Stream/River Water Quality Data	CY 2018 - 2020
Lake Water Quality Data	CY 2016 - 2020
Biological Sampling Data	CY 2016 - 2020*
Fish Kill Data	CY 2016 - 2020
Fish Tissue Sampling Data	CY 2016 - 2020
Continuous Dissolved Oxygen Sampling Data	CY 2016 - 2020
*Biological sites sampled in both 2015 and 2019 were also assessed.

Open Segment Map
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Cycle: 2022
Release Status: Final
Overall IR: 4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
Trend: Unknown
Created: 1/10/2022 2:26:17 PM
Updated: 2/9/2022 10:09:48 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

2012

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Ambient monitoring: USGS

Class BWW1

Aquatic Life - Warm Water Type 1

Not Assessed

Class HH

Human Health -

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 use was assessed as “not supported” due to 2014-2016 levels of indicator bacteria that slightly exceed state water quality criteria. All other designated uses were "not assessed." Historically, water quality and fish tissue data collected in Segment 622 were used to assess this segment. Beginning with the 2020 IR, segment assessments are based only on data collected in that segment. 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

Sources of Data:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2014-2016	10580003	Iowa River near Wapello	Site located in Seg 622, no longer used to assess this segment

Class A1 - Indicator Bacteria:

Site ID	Data Source ID	# Samples / # Years	2014 Geometric Mean	2015 Geometric Mean	2016 Geometric Mean	Annual Geometric Mean Violation	# Violations	% Violations	Significantly >10% Violations	Assessment Type	Support Level
10580003	6	18 / 3	10	80	202	Yes	5	28%	Yes	Evaluated	Not

Monitoring and Methods

Assessment Key Dates

1/8/2014

Fixed Monitoring Start Date

12/6/2016

Fixed Monitoring End Date

3/9/2018

TMDL Completed

Methods

150

Monitoring data more than 5 years old

420

Indicator bacteria monitoring