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 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
View assessment methodology in new window

Cycle: 2020
Release Status: Final
Overall IR: 5 - Water is impaired or threatened and a TMDL is needed.
Trophic: Eutrophic
Trend: Stable
Created: 7/29/2020 2:14:40 PM
Updated: 10/14/2020 10:23:33 AM

Use Support

Class A1

Recreation - Primary contact

Partially Supported

Bacteria: Indicator Bacteria- E. coli

Support Level

Partially Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Moderate

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

Moderate

Cycle Added

2006

Impairment Rationale

Geometric mean criterion exceeded

Data Source

Beach monitoring: Iowa DNR WQMA

TMDL Priority

Tier II

Turbidity

Support Level

Partially 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

Class BLW

Aquatic Life - Lakes and wetlands

Partially Supported

Turbidity

Support Level

Partially 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 -

Not Assessed

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 “partially supported” due levels of indicator bacteria that exceed the state water quality standard. Aesthetically objectionable conditions due to low water clarity also cause an impairment at this lake. The Class BLW uses are assessed (evaluated) as “partially supported” based on information from the IDNR Fisheries Bureau that suggests that siltation remains a problem at Rock Creek Lake. The Class C uses are “not assessed” due to a lack of enough information upon which to base an assessment. Class HH uses remain (evaluated) “fully supported” based on fish tissue monitoring in 2013. Note: A TMDL for siltation and nutrients at Rock Creek Lake was prepared by DNR and approved by EPA in 2001. Because the Section 303(d) impairment due to indicator bacteria (aka, "pathogens") was not addressed in the TMDL, this waterbody was will remain in Category 5a (impaired; TMDL required) for this assessment/listing cycles.

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 2016-2017	21500001	Rock Creek Beach (Rock Creek State Park)
Iowa DNR	6	WQ	CY 2014-2018	22500001	Rock Creek Max Depth
Iowa DNR		FT	See Below	326	Rock Creek

Class A1 - Indicator Bacteria:

Site ID	Data Source ID	# Samples / # Years	2016 Geometric Mean	2017 Geometric Mean	2018 Geometric Mean	Annual Geometric Mean Violation	# Violations	% Violations	Significantly >10% Violations	Assessment Type	Support Level
21500001	6	18 / 2	78.81	160	NA	Yes	1	6%	YES	Monitored	Partial

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
22500001	6	15 / 5	9.1	8.3	8.2	1	7%	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
22500001	6	Chlorophyll a TSI	15 / 5	36	77	61	NO	Monitored	Full
22500001	6	Secchi TSI	15 / 5	59	83	67	YES	Monitored	Not
22500001	6	Total Phosphorus TSI	15 / 5	59	82	71	NA	NA	NA
22500001	6	Inorganic suspended solids	15 / 5	0.3	32	9.6	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
22500001	6	Ammonia	15 / 5	0.55705	0.12	0.1	0 / 0	0% / 0%	NO	Monitored	Full
22500001	6	Dissolved oxygen	15 / 5	16	9	9	NA / 0	NA / 0%	NO	Monitored	Full
22500001	6	pH	15 / 5	9.1	8.3	8.2	1 / NA	7% / NA	NO	Monitored	Full
22500001	6	Temperature	15 / 5	28.5	23.49	23.9	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
22500001	6	11	101.254	99.7 %	15.547	62.1 %	NO	Evaluated	NA

Class C - Conventional Parameters:

Site ID	Data Source ID	Parameter Name	# Samples / # Years	Maximum Value	Mean Value	Median Value	# Violations	% Violations	Significantly >10% Violations	Assessment Type	Support Level
22500001	6	Inorganic nitrogen (nitrate and nitrite)	15 / 5	6.2	1.9	1.6	0	0%	NO	Monitored	Full

The Class C uses are not assessed due to the lack of data sufficient for developing a valid assessment of support of the Class C uses.

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

326

9/16/13

largemouth bass

plug

0.116

Evaluated

Full

326

10/2/13

channel catfish

fillet

<0.2

<0.6

<0.05

Evaluated

Full

Monitoring and Methods

Assessment Key Dates

6/23/2014

Fixed Monitoring Start Date

9/9/2018

Fixed Monitoring Start Date

9/16/2013

Fish Tissue Monitoring

1/28/2002

TMDL Completed

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)

420

Indicator bacteria monitoring