2020 assessment for Little Rock River

Little Rock River IA 06-BSR-1799

from confluence with Otter Cr. (NW 1/4 S21 T98N R44W Lyon Co.) to confluence with Argo Slough in S17 T99N R43W Lyon Co.

2020
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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Overall IR

5 - Water is impaired or threatened and a TMDL is needed.

Trend

Unknown

Created

6/11/2020 6:50:34 AM by

Updated

4/16/2021 12:42:35 PM by

Use Support

Class A1

Presumptive Use

Recreation - Primary contact

Not Assessed

Class BWW2

Aquatic Life - Warm Water Type 2

Partially Supported

Biological: low aquatic macroinvertebrate IBI

Support Level

Partially Supported

Impairment Code

5b-v - Biological - verified

Cause Magnitude

Slight

303(d) Listing Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

Low

Cycle Added

2014

Impairment Rationale

Low Biotic Index

Data Source

Biological monitoring: Iowa DNR WQMA

TMDL Priority

Tier IV

General Use

General Use water -

Not Assessed

303(d) Delistings for this Cycle

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class BWW2 use was assessed as "partially supported" based on biological sampling data. The Class BWW2 use previously resided in Category 4d based on 2011 fish kill. This segment’s fish community was sampled in 2011, 2014, and 2019 as part of the DNR fish kill follow-up sampling program. Based on the results of the fish kill follow-up sampling, the Category for the fish kill assessment was changed from 4d to 3a (water not assessed). 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	BIO	See Below	64	Little Rock River	Little Rock CWA - George

Presumptive Class A1 - No Data

Class BWW2 – Fish kill Follow-Up Assessment:

BioNet Site ID	Stream Name	Site Type	Ecoregion	Sample Date	Fish per mile	REMAP 25 % fish/mile	>REMAP 25 % fish/mile?	2000 305(b) fish taxa present	2000 305(b) fish taxa present %
64	Little Rock River	Wadeable	47a	8/27/19	819	524	Yes (Pass)	9/9	100% (Pass)
64	Little Rock River	Wadeable	47a	9/16/14	2248	524	Yes (Pass)	8/9	89% (Pass)
64	Little Rock River	Wadeable	47a	9/28/11	1041	524	Yes (Pass)	8/9	89% (Pass)
The Class BWW2 aquatic life use previously resided in Category 4d based on 2011 fish kill. This segment’s fish community was sampled in 2011, 2014, and 2019 as part of the DNR fish kill follow-up sampling program. The results from this follow-up sampling and comparison to ecoregion averages suggest that the fish community of this segment is similar to non-fish kill impacted streams. Based on the results of the fish kill follow-up sampling, the Category for the fish kill assessment was changed from 4d to 3a (water not assessed).

Class BWW2 - Biological Sampling:

Benthic Macroinvertebrates:

BioNet Site ID	Date	Drainage Area (mi2)	Ecoregion	Major Drainage/ Thermal	BM Sample Gear	BMIBI score	BMIBI Class	47a BMIBI BIT	BMIBI Pass/ Fail
64	8/27/19	180	47a	MO/WW	Float ArtSub	63	Good	54	Pass
64	9/16/14	180	47a	MO/WW	ArtSub	52	Fair	54	Fail
64	9/28/11	180	47a	MO/WW	Hess	48	Fair	54	Fail

Fish:

BioNet Site ID	Date	Drainage Area (mi2)	Ecoregion	Major Drainage/ Thermal	Riffle Stream?	FIBI score	FIBI Class	47a FIBI BIT	FIBI Pass/ Fail
64	8/27/19	180	47a	MO/WW	NA	63	Good	43	Pass
64	9/16/14	180	47a	MO/WW	NA	42	Fair	43	Fail
64	9/28/11	180	47a	MO/WW	NA	61	Good	43	Pass

Overall:

Community	Assessment Type	Assessment Result	Support Level	Earned IR Category	Actual IR Category	Reason
Benthic Macroinvertebrates	Evaluated	Fail (1/3)	Partial
Fish	Evaluated	Pass (2/3)	Full
Overall	Evaluated	Fail	Partial	3bc	5bv	Assessment is evaluated because it included samples not collected in the last five years.

Monitoring and Methods

Assessment Key Dates

9/28/2011

Biological Monitoring

4/1/2011

Fish Kill

9/16/2014

Biological Monitoring

8/27/2019

Biological Monitoring

Methods

150

Monitoring data more than 5 years old

315

Regional reference site approach

320

Benthic macroinvertebrate surveys

330

Fish surveys