Big Creek Lake IA 04-UDM-1242

Polk County S22T81NR25W near Polk City

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: 12/30/2021 9:04:33 AM
Updated: 1/28/2022 7:14:42 AM

Use Support

Class A1

Recreation - Primary contact

Not Supported

Bacteria: Indicator Bacteria- E. coli

Support Level

Not Supported

Impairment Code

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

Cause Magnitude

Moderate

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

Moderate

Cycle Added

2006

Impairment Rationale

Single-sample maximum criterion exceeded in significantly > 10% of samples

Data Source

Beach monitoring: Iowa DNR WQMA

Algal Growth: Chlorophyll a

Support Level

Not Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Slight

Status

Continuing

Source

Agriculture

Source Confidence

Moderate

Cycle Added

2020

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

TMDL Priority

Tier I

Class BWW1

Aquatic Life - Warm Water Type 1

WINOFI

Fish Kill: Due To Natural Causes

Support Level

Further Investigation Needed

Impairment Code

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

Cause Magnitude

Slight

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

Low

Cycle Added

2016

Impairment Rationale

Non Pollutant-caused fish kill

Data Source

Biological monitoring: Iowa DNR Fisheries

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 violations of the state water quality criteria for indicator bacteria and secondarily by the presence of aesthetically objectionable conditions caused by algal blooms. The Class BWW1 use was assessed (evaluated) as “WINOFI” based on the results of a fish kill investigation and information from the DNR Fisheries Bureau. The Class HH (fish consumption) use was assessed (monitored) as “fully supported” based on fish tissue sampling data. Note: The DNR TMDL for the impairment due to indicator bacteria at this lake was approved by U.S. EPA in August 2011. Because this TMDL does not address all of the impairments identified for this lake (Algal Growth: Chlorophyll a), this lake remains in IR Category 5a (impaired; TMDL required).

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2018-2020	21770001	Big Creek Beach (Big Creek State Park)
Iowa DNR	6	WQ	CY 2016-2020	22770004	Big Creek	Lake Deep Point
Iowa DNR	6	WQ	CY 2016-2019	26770002	Big Creek 319 (BCL4)	TMDL north arm sampling point
Iowa DNR	6	WQ	CY 2016-2019	26770003	Big Creek 319 (BCL3)	TMDL central sampling point
Iowa DNR	6	WQ	CY 2016-2019	26770004	Big Creek 319 (BCL5)	TMDL west arm sampling point
Iowa DNR	6	FT	See Below	52	Big Creek Lake	NW of Polk City

Class A1 - Indicator Bacteria:

Site ID

Data Source ID

# Samples per Year (2018/ 2019/2020)

2018 Geometric Mean

2019 Geometric Mean

2020 Geometric Mean

Violates Annual Geometric Mean?

# 2018 SSM violations / SSM Violations needed for impairment

# 2019 SSM violations / SSM Violations needed for impairment

# 2020 SSM violations / SSM Violations needed for impairment

Violates Annual SSM Significantly >10% Rule?

Assessment Type

Support Level

21770001

6/0/12

0 / NA

2 / 4

Monitored

Full

22770004

7/4/0

0 / 3

0 / NA

Monitored

Full

26770002

7/4/0

1 / 3

0 / NA

Monitored

Full

26770003

7/4/0

0 / 3

0 / NA

Monitored

Full

26770004

7/4/0

1 / 3

0 / NA

Monitored

Full

According to DNR's methodology, a lake must meet water quality standards for two consecutive cycles to suggest de-listing. Therefore, Big Creek will remain listed for the 2022 cycle as "not supported" its Class A1 use due to Ecoli bacteria.

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
22770004	6	15 / 5	7.5	8.4	8.1	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
22770004	6	Chlorophyll a TSI	42 / 5	26	79	64	NO	Monitored	Full
22770004	6	Secchi TSI	15 / 5	37	70	62	NO	Monitored	Full
22770004	6	Total Phosphorus TSI	42 / 5	54	77	65	NA	NA	NA
22770004	6	Inorganic suspended solids	15 / 5	0.3	10	2	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 Big Creek 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, Big Creek will remain listed as "not supported" for the 2022 assessment/listing cycle.

Class BWW1 - 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
22770004	6	Ammonia	15 / 5	0.011	0.196	0.08	NA	0 / 0	4	NO	Monitored	Full
22770004	6	Dissolved Oxygen	14 / 5	3.7	10.7	7.4	2	NA / NA	4	NO	Monitored	Full
22770004	6	pH	15 / 5	7.5	8.4	8.1	0	NA / NA	4	NO	Monitored	Full
22770004	6	Temperature	15 / 5	14.2	27.7	22.7	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
22770004	6	6	12.61	28.2%	0.83	7.5%	NO	Evaluated	NA

Class BLW - Fish Kill:

The Class BLW use was assessed (evaluated) as “WINOFI” due to a fish kill that occurred in 2017. Because the cause of the fish kill was not identified, or the fish kill was attributed to a non-pollutant cause (e.g., winterkill), the assessment type is “evaluated.” Segments assessed using “evaluated” assessments are placed in Category 3b and are added to the state list of waters in need of further investigation. If no additional fish kills are reported in the segment for a 10 year period, the Category will be changed from 3b to 3a (water not assessed).

Details about the 2017 fish kill can be found here: https://programs.iowadnr.gov/fishkill/Events/942

Class HH - Toxic Parameters: No Data

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)
52	tissue plug	2019	largemouth bass	10	34.2	0.063
52	tissue plug	2017	largemouth bass	3	41.1	0.097
52	tissue plug	2019	walleye	20	47.9	0.057
Support Level	Full

Monitoring and Methods

Assessment Key Dates

4/14/2016

Non-fixed Monitoring Start Date

8/31/2020

Non-fixed Monitoring End Date

8/24/2011

TMDL Completed

6/14/2017

Fish Tissue Monitoring

7/1/2019

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)

420

Indicator bacteria monitoring