Rock Creek Lake IA 03-NSK-865

Jasper County S17T80NR17W 4 mi. ENE of Kellogg.

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.
Trophic: Hypereutrophic
Trend: Stable
Created: 11/1/2023 8:12:55 AM
Updated: 2/2/2024 2:33:54 PM

Use Support

Class A1

Recreation - Primary contact

Not Supported

Turbidity

Support Level

Not Supported

Impairment Code

4a - Pollutant-caused impairment. TMDL has been completed.

Cause Magnitude

Moderate

Status

Continuing

Source

Other: Sediment Resuspension

Source Confidence

Moderate

Cycle Added

2014

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

Algal Growth: Chlorophyll a

Support Level

Not Supported

Impairment Code

4a - Pollutant-caused impairment. TMDL has been completed.

Cause Magnitude

Slight

Status

New

Source

Agriculture

Source Confidence

Moderate

Cycle Added

2024

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

Class BLW

Aquatic Life - Lakes and wetlands

Not Supported

Turbidity

Support Level

Not Supported

Impairment Code

4a - Pollutant-caused impairment. TMDL has been completed.

Cause Magnitude

Moderate

Status

Continuing

Source

Agriculture

Source Confidence

Moderate

Cycle Added

2010

Impairment Rationale

Adverse impacts on plant/animal communities

Data Source

Biological monitoring: Iowa DNR Fisheries

Class C

Drinking Water -

Fully Supported

Class HH

Human Health -

Fully Supported

Impairment Delistings

Cycle Added	Class	Cause	Data Source	Rationale
2006	Class A1	Bacteria: Indicator Bacteria- E. coli	Beach monitoring: Iowa DNR WQMA	New data: WQ improvement (chemical / physical / bacterial)

Documentation

Assessment Summary

The Class A1 use was assessed (monitored) as “not supported” due to aesthetically objectionable conditions due to low water clarity and algae blooms also caused an impairment at this lake. The Class BLW use was assessed (evaluated) as “not supported” based on information from the DNR Fisheries Bureau that suggested that siltation remains a problem at Rock Creek Lake. The Class C (drinking water) use was assessed as "fully supported" based on water quality monitoring data. The Class HH (fish consumption) use remains assessed as “fully supported” based on fish tissue sampling data. Note: A TMDL for siltation and nutrients at Rock Creek Lake was prepared by DNR and approved by EPA in 2001. Because all of the Section 303(d) impairment were addressed in the TMDL, this waterbody was will move form Category 5a (impaired; TMDL required) to 4a (TMDL has been completed) for this assessment/listing cycles.

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2020-2022	14000173	RKCRK 1
Iowa DNR	6	WQ	CY 2020-2020	14000174	RKCRK 2
Iowa DNR	6	WQ	CY 2020-2020	14000175	RKCRK 3
Iowa DNR	6	WQ	CY 2020-2020	14000176	RKCRK 4
Iowa DNR	6	WQ	CY 2020-2020	14000177	RKCRK 5
Iowa DNR	6	WQ	CY 2020-2022	21500001	Rock Creek Beach
Iowa DNR	6	WQ	CY 2018-2022	22500001	Rock Creek Max Depth
Iowa DNR	6	FT	See Below	1324	Rock Creek	Rock Creek State Park

Class A1 - Indicator Bacteria:

Site ID

Data Source ID

# Samples per Year (2020/ 2021/2022)

2020 Geometric Mean

2021 Geometric Mean

2022 Geometric Mean

Violates Annual Geometric Mean?

# 2020 SSM violations / SSM Violations needed for impairment

# 2021 SSM violations / SSM Violations needed for impairment

# 2022 SSM violations / SSM Violations needed for impairment

Violates Annual SSM Significantly >10% Rule?

Assessment Type

Support Level

14000173

4/3/4

0 / NA

Evaluated

Full

14000174

4/3/4

0 / NA

Evaluated

Full

14000175

5/3/4

0 / NA

Evaluated

Full

14000176

5/3/4

0 / NA

Evaluated

Full

14000177

5/3/4

0 / NA

Evaluated

Full

21500001

11/14/14

2 / 3

0 / 4

Mon

Full

22500001

8/3/3

0 / 3

0 / NA

Mon

Full

Rock Creek Lake was assessed as "not supported" for the 2006 assessment/listing cycle. Based on DNR’s assessment methodology, the current assessment/listing cycle must be without violations of the geometric mean criterion and without significantly greater than 10% of the samples violating the single-sample maximum criterion to propose delisting based on bacteria violations. There were no violations of the geometric mean criterion and there were less than 10% of the samples exceeding the single-sample maximum criterion for the current 2024 assessment listing cycle. Therefore, the impairment for indicator bacteria is suggested for delisting for the 2024 assessment/listing cycle.

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
22500001	6	21 / 5	7.5	9.1	8.5	2	5	NO	Mon	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
22500001	6	Chlorophyll a TSI	15 / 5	48	80	67	YES	Mon	Not
22500001	6	Secchi TSI	21 / 5	65	83	75	YES	Mon	Not
22500001	6	Total Phosphorus TSI	15 / 5	37	87	76	NA	NA	NA
22500001	6	Inorganic suspended solids	15 / 5	0.6	32	11	NA	NA	NA

Class BLW - Binomial 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
22500001	6	Dissolved Oxygen	21 / 5	6.3	16	9.6	0	NA / NA	5	NO	Mon	Full
22500001	6	pH	21 / 5	7.5	9.1	8.5	2	NA / NA	5	NO	Mon	Full
22500001	6	Temperature	21 / 5	17.1	28.5	23.9	0	NA / NA	5	NO	Mon	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
22500001	6	6	45.55864619	84%	12.56693869	43%	NO	Evaluated	NA

Class BLW - Toxic Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Maximum Value	Mean Value	Median Value	# Acute / Chronic Violations	>1 Acute / Chronic Violation	Assessment Type	Support Level
22500001	6	Ammonia	15 / 5	0.8183	0.12	0.04	0 / 0	NO	Mon	Full

Class C - Binomial Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Minimum Value	Maximum Value	Mean Value	Median Value	# Violations	Violates Significantly >10% Rule?	Assessment Type	Support Level
22500001	6	Inorganic nitrogen (nitrate and nitrite)	14 / 5	0.02	3.12	0.92	0.51	0	NO	Mon	Full
22500001	6	pH	21 / 5	7.5	9.1	8.5	8.5	2	NO	Mon	Full

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)
1324	fillet	2013	channel catfish	3	43	0.05	<0.2	<0.6
1324	tissue plug	2013	largemouth bass	5	42.7	0.116
Support Level	Full

Monitoring and Methods

Assessment Key Dates

6/12/2018

Monitoring Start

9/28/2022

Monitoring End

9/16/2013

Fish Tissue Monitoring

1/28/2002

TMDL Completed

Methods

150

Monitoring data more than 5 years old

200

Physical/Chemical Monitoring

260

Fish tissue analysis

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)

420

Indicator bacteria monitoring