Shell Rock River IA 02-SHL-786

from confluence with the Winnebago River (Floyd Co.) to confluence with Rose Cr. in NW 1/4 S8 T97N R18W Cerro Gordo 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 2020 - 2022
Stream/River Water Quality Data	CY 2020 - 2022
Lake Water Quality Data	CY 2018 - 2022
Biological Sampling Data	CY 2018 - 2022*
Fish Kill Data	CY 2018 - 2022
Fish Tissue Sampling Data	CY 2018 - 2022
Continuous Dissolved Oxygen Sampling Data	CY 2018 - 2022
*Biological sites sampled in both 2017 and 2021 were also assessed.

Open Segment Map
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Cycle: 2024
Release Status: Final
Overall IR: 4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
Trend: Unknown
Created: 11/1/2023 8:12:36 AM
Updated: 12/29/2023 10:39:01 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

2006

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Ambient monitoring: USGS

Class BWW1

Aquatic Life - Warm Water Type 1

Fully Supported

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” based on levels of indicator bacteria (E. coli) that violated state water quality criteria. The Class BWW1 use was assessed as "fully supported" based on biological sampling data. All other designated uses were "not assessed." Note: A TMDL for indicator bacteria in this segment of the Shell Rock River was approved by EPA in February 2010; therefore, the Class A1 use impairment was moved from IR Category 5a to IR Category 4a.

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	BIO	See Below	1032	Shell Rock River	Rockford Impoundment
Iowa DNR	6	BIO	See Below	1033	Shell Rock River	Rockford below dam
Iowa DNR	6	BIO	See Below	1034	Shell Rock River	Nagle Wildlife Area
Iowa DNR	6	WQ	CY 2002-2004	11340001	Shell Rock River at Rockford

Class A1 - Indicator Bacteria:

Site ID	Data Source ID	# Samples / # Years	2002-2004 Geometric Mean	Annual Geometric Mean Violation	# Violations	% Violations	Significantly >10% Violations	Assessment Type	Support Level
11340001	6	22 / 3	72	No	5	22%	Yes	Evaluated	Not

Class BWW1 - Biological Sampling:

Fish:

Site ID	Date	Drainage Area (mi2)	Ecoregion	Major Drainage	Riffle Stream?	FIBI score	FIBI Class	47c FIBI BIT	FIBI Pass/ Fail
1032	8/6/19	529	47c	MS	Undetermined	58	Good	44	Pass
1033	8/6/19	531	47c	MS	Undetermined	60	Good	44	Pass
1034	8/5/19	517	47c	MS	Undetermined	61	Good	44	Pass
1034	8/15/18	517	47c	MS	Undetermined	74	Excellent	44	Pass
1032	8/14/18	529	47c	MS	Undetermined	57	Good	44	Pass
1033	8/14/18	531	47c	MS	Undetermined	71	Excellent	44	Pass
1034	7/26/17	517	47c	MS	Undetermined	43	Fair	44	Fail
1032	7/25/17	529	47c	MS	Undetermined	39	Fair	44	Fail
1033	7/25/17	531	47c	MS	Undetermined	41	Fair	44	Fail

Overall:

Community	Assessment Type	Assessment Result	Support Level	IR Category	Reason
Fish	Evaluated	Pass (6/9)	Full		Assessment was evaluated because the drainage areas of the sites used for
Overall	Evaluated	Pass	Full	1	the assessment were greater than the calibrated range.

Class HH – No Data

Monitoring and Methods

Assessment Key Dates

1/8/2002

Monitoring Start

12/8/2004

Monitoring End

7/25/2017

Biological Monitoring

7/26/2017

Biological Monitoring

8/14/2018

Biological Monitoring

2/1/2010

TMDL Completed

8/15/2018

Biological Monitoring

8/5/2019

Biological Monitoring

8/6/2019

Biological Monitoring

Methods

150

Monitoring data more than 5 years old

315

Regional reference site approach

330

Fish surveys

420

Indicator bacteria monitoring