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 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.

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Cycle: 2022
Release Status: Final
Overall IR: 5 - Water is impaired or threatened and a TMDL is needed.
Trophic: Eutrophic
Trend: Stable
Created: 12/27/2021 3:06:25 PM
Updated: 2/1/2022 9:29:21 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

5* - 303(d)-impaired last cycle; fully supporting this cycle; potential de-listing.

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

Continuing

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

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 use was assessed (monitored) as “not supported” due to poor water transparency caused by high levels of inorganic turbidity and algae. The Class BLW use was assessed (monitored) as "not supported" due to violations of the Class BLW criterion for dissolved oxygen. Additionally, the Class BLW use was assessed (evaluated) as “WINOFI” (IR 3b) due to high levels of inorganic turbidity. The Class HH use was assessed as "fully supported" based on fish tissue sampling data.

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2016-2020	22630002	Roberts Creek Lake
Iowa DNR	6	FT	See Below	325	Roberts Creek Lake	N of Red Rock Reservoir

Class A1 - Indicator Bacteria: No Data

Class A1 - pH:

Site ID	Data Source ID	# Samples / # Years	Minimum Value	Maximum Value	Mean Value	# Violations	Violations needed for impairment	Violates Significantly >10% Rule?	Assessment Type	Support Level
22630002	6	15 / 5	7.3	8.6	7.9	0	4	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
22630002	6	Chlorophyll a TSI	15 / 5	36	77	63	NO	Monitored	Full
22630002	6	Secchi TSI	15 / 5	51	83	70	YES	Monitored	WINOFI
22630002	6	Total Phosphorus TSI	15 / 5	61	79	73	NA	NA	NA
22630002	6	Inorganic suspended solids	15 / 5	0.6	23	9	NA	NA	NA

Although the index value for Chlorophyll a is below the impairment trigger of 65 for this assessment cycle, the Class A1 use of Roberts Creek Lake remains "not supported" due to aesthetically objectionable conditions. Based on DNR's methodology, the median TSI value for Chlorophyll a must be 63 or less for two consecutive assessment/listing cycles before a lake can be removed from the state's Section 303(d) list (IR Category 5). Therefore, Roberts Creek Lake will remain listed as "not supported" for the 2022 assessment/listing cycle.

Class BLW - Conventional Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Minimum Value	Maximum Value	Mean Value	# Violations	# Acute / Chronic Violations	Violations needed for impairment	Violates Significantly >10% Rule?	Assessment Type	Support Level
22630002	6	Ammonia	15 / 5	0.0003	0.6066	0.15	NA	0 / 0	4	NO	Monitored	Full
22630002	6	Dissolved Oxygen	15 / 5	3.2	9.2	6.1	5	NA / NA	4	YES	Monitored	Not
22630002	6	pH	15 / 5	7.3	8.6	7.9	0	NA / NA	4	NO	Monitored	Full
22630002	6	Temperature	15 / 5	19	27.6	23.6	0	NA / NA	4	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 Concentration = 75th Percentile	Assessment Type	Support Level
22630002	6	6	14.92	65.4%	6.21	43.0%	NO	Evaluated	NA

Class HH - Fish Tissue Sampling:

Site ID	Biopart	Year	Species	# in sample / # of samples	Avg Length (cm)	(Avg) Hg (ppm)	Chlordane (ppm)	Sum PCBs (ppm)
325	tissue plug	2017	largemouth bass	3	41	0.143
Support Level	Full

Monitoring and Methods

Assessment Key Dates

6/22/2016

Non-fixed Monitoring Start Date

9/10/2020

Non-fixed Monitoring End Date

7/1/2017

Fish Tissue Monitoring

Methods

120

Surveys of fish and game biologists/other professionals

222

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

260

Fish tissue analysis

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)