Shell Rock River IA 02-SHL-784

from confluence with Flood Cr. (S27 T93N R16W Butler Co.) to confluence with Winnebago R. in S14 T96N R18W Floyd 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 2016 - 2018
Stream/River Water Quality Data	CY 2016 - 2018
Lake Water Quality Data	CY 2014 - 2018
Biological Sampling Data	CY 2014 - 2018*
Fish Kill Data	CY 2014 - 2018
Fish Tissue Sampling Data	CY 2014 - 2018
Continuous Dissolved Oxygen Sampling Data	CY 2014 - 2018
*Biological sites sampled in both 2013 and 2017 were also assessed.

Open Segment Map
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Cycle: 2020
Release Status: Final
Overall IR: 5 - Water is impaired or threatened and a TMDL is needed.
Trend: Unknown
Created: 8/12/2020 7:36:21 AM
Updated: 10/14/2020 1:41:54 PM

Use Support

Class A1

Presumptive Use

Recreation - Primary contact

Not Assessed

Class BWW1

Aquatic Life - Warm Water Type 1

Not Assessed

Class HH

Human Health -

Partially Supported

Fish Consumption Advisory: Mercury

Support Level

Partially Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Moderate

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2012

Impairment Rationale

Fish consumption advisory in effect: no more than 1 meal/week

Data Source

Fish contaminant monitoring: Iowa DNR

TMDL Priority

Tier IV

General Use

General Use water -

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class HH use remains assessed as "partially supported" based on fish tissue sampling data and due to the existence of a one meal per week fish consumption advisory for mercury. All other designated uses were "not assessed".

Assessment Explanation

Sources of Data:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	FT	See Below	68	Shellrock River W of Clarksville	Site located in Segment 783

Class A1 - No Data

Class BWW1 - No Data

Class HH – Fish Tissue Sampling:

Site ID

Date

Species Name

Biopart

# in sample

chlordane result

chlordane violation (>0.6)?

PCBs result

PCBs violation (>0.2)?

Hg result

Hg violation (>0.3)?

Assessment Type

Support Level

8/2/2012

walleye

plug

0.285

Evaluated

Full

8/23/2011

walleye

plug

0.753

Yes

Evaluated

Partial

8/23/2011

common carp

fillet

<0.03

<0.09

0.206

Evaluated

Full

Follow-up monitoring was conducted in 2012 to better define the level of mercury in Shell Rock River fish and to provide information for any changes needed to the consumption advisory. Results showed that the average level of mercury in tissue samples fr0m three Walleye was just below the consumption advisory threshold of 0.3 ppm (ave = 0.285, sd = 0.078).

A one meal/week consumption advisory for mercury exists on this segment of the Shell Rock River – seeIowa Consumption Advisories

Because a one meal per week fish consumption advisory covers this waterbody, the fish consumption uses are assessed as “partially supported.”

Monitoring and Methods

Assessment Key Dates

8/23/2011

Fish Tissue Monitoring

8/2/2012

Fish Tissue Monitoring

Methods

150

Monitoring data more than 5 years old

260

Fish tissue analysis