Roberts Creek Lake IA 04-LDM-1019

Marion County S4T76NR19W 6 mi NE of Knoxville.

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.

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Cycle: 2020
Release Status: Final
Overall IR: 5 - Water is impaired or threatened and a TMDL is needed.
Trophic: Eutrophic
Trend: Stable
Created: 8/12/2020 10:21:29 AM
Updated: 10/14/2020 10:48:32 AM

Use Support

Class A1

Recreation - Primary contact

Not Supported

Turbidity

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

High

Status

Continuing

Source

Other: Sediment Resuspension

Source Confidence

High

Cycle Added

2004

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

TMDL Priority

Tier I

Algal Growth: Chlorophyll a

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Moderate

Status

Continuing

Source

Agriculture

Source Confidence

Moderate

Cycle Added

2018

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

TMDL Priority

Tier I

Class BLW

Aquatic Life - Lakes and wetlands

Not Supported

Turbidity

Support Level

Further Investigation Needed

Impairment Code

3b - Use potentially impaired based on an evaluated assessment.

Cause Magnitude

High

Status

Continuing

Source

Other: Sediment Resuspension

Source Confidence

High

Cycle Added

2006

Impairment Rationale

Adverse impacts on plant/animal communities

Data Source

Biological monitoring: Iowa DNR Fisheries

Organic Enrichment: Low Dissolved Oxygen

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Moderate

Status

New

Source

Unknown: Source Unknown

Source Confidence

Low

Cycle Added

2020

Impairment Rationale

Significantly > 10% of samples fail to meet criterion

Data Source

Ambient monitoring: Iowa DNR-lakes

TMDL Priority

Tier I

Class HH

Human Health -

Fully Supported

General Use

General Use water -

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 uses are assessed (monitored) as “not supported” due to poor water transparency caused by high levels of inorganic turbidity and algae. The Class BLW uses are assessed (monitored) as "not supported" due to violations of the Class BLW criterion for Dissolved Oxygen. Additionally, the Class BLW uses are assessed(evaluated) as “partially supported” (IR 3b) due to high levels of inorganic turbidity. The Class HH uses are assessed as "fully supporting" based on fish tissue sampling.

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 2014-2018	22630002	Roberts Creek Lake	Lake Deep Point
Iowa DNR	6	WQ	CY 2015-2015	14000161	Roberts Creek Lake	TMDL Sampling Point RobCrk1
Iowa DNR	6	WQ	CY 2015-2015	14000162	Roberts Creek Lake	TMDL Sampling Point RobCrk2
Iowa DNR		FT	See Below	325	Roberts Creek Lake

Class A1 - Indicator Bacteria: No Data

Class A1 - pH:

Site ID	Data Source ID	# Samples / # Years	Maximum Value	Mean Value	Median Value	# Violations	% Violations	Significantly >10% Violations	Assessment Type	Support Level
22630002	6	15 / 5	8.5	8	8	0	0%	NO	Monitored	Full

Class A1 - Lake TSI's

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Minimum Value	Maximum Value	Median Value	Median TSI Violation	Assessment Type	Support Level
14000161	6	Chlorophyll a TSI	12 / 1	62	79	69	YES	Monitored	Not
14000162	6	Chlorophyll a TSI	12 / 1	64	75	68	YES	Monitored	Not
22630002	6	Chlorophyll a TSI	27 / 5	36	75	67	YES	Monitored	Not
22630002	6	Secchi TSI	15 / 5	59	77	70	YES	Monitored	Not
14000161	6	Total Phosphorus TSI	13 / 1	63	81	75	NA	NA	NA
14000162	6	Total Phosphorus TSI	13 / 1	63	78	73	NA	NA	NA
22630002	6	Total Phosphorus TSI	28 / 5	62	81	72	NA	NA	NA
22630002	6	Inorganic suspended solids	15 / 5	3.5	23	9	NA	NA	NA

Class BLW - Conventional Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Maximum Value	Mean Value	Median Value	# Acute / Chronic Violations	% Acute/ Chronic Violations	Significantly >10% Violations	Assessment Type	Support Level
22630002	6	Ammonia	15 / 5	0.426	0.12	0.07	0 / 0	0% / 0%	NO	Monitored	Full
22630002	6	Dissolved oxygen	15 / 5	9.6	6.5	6.8	NA / 5	NA / 33%	YES	Monitored	Not
22630002	6	pH	15 / 5	8.5	8	8	0 / NA	0% / NA	NO	Monitored	Full
22630002	6	Temperature	15 / 5	26.2	23.66	24.02	0 / 0	0% / 0%	NO	Monitored	Full

Class BLW - Lake Planktonic Cyanobacteria:

Site ID	Data Source ID	# Samples	Maximum Cyanobacteria Wet Mass	Maximum Cyanobacteria % Composition	Median Cyanobacteria Wet Mass	Median Cyanobacteria % Composition	Median Cyanobacteria Wet Mass = 75th Percentile	Assessment Type	Support Level
22630002	6	11	65.368	87.7 %	5.904	43.8 %	NO	Evaluated	NA

Class HH - Fish Tissue Sampling:

Site ID

Date

Species Name

Biopart

# in sample

chlordane result

chlordane violation?

PCBs result

PCBs violation?

Hg result

Hg violation?

Assessment Type

Support Level

325

6/14/17

largemouth bass

plug

0.143

Monitored

Full

Monitoring and Methods

Assessment Key Dates

6/23/2014

Fixed Monitoring Start Date

9/9/2018

Fixed Monitoring End Date

Methods

120

Surveys of fish and game biologists/other professionals

222

Non-fixed-station monitoring (conventional during key seasons and flows)

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)