Mill Creek Lake IA 06-LSR-1616

O'Brien County S3T95NR41W 0.25 mi E of Paullina

Assessment Cycle

2024

Release Status

Final

Data Collection Period

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.

Overall IR Category: 2 - Some of the designated uses are met but there is insufficient data to determine if remaining designated uses are met.
Trophic: Eutrophic
Trend: Improving
Trend Comment: The Chlorophyl a TSI values continue to show improvement. Because of this the 2018 Algal Growth: Chlorophyll a impairment was able to be delisted in during the 2022 listing cycle.

Created: 11/1/2023 8:13:30 AM
Updated: 12/22/2023 2:48:01 PM

Assessment conducted in accordance with Iowa's 2024 IR methodology

Use Support

Class A1

Recreation

Primary contact

Fully Supported

Class BLW

Aquatic Life

Lakes and wetlands

WINOFI

Further Investigation Needed

Support Level

Water in Need of Further Investigation (WINOFI)

Impairment Code

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

Cause Magnitude

Slight

Status

Continuing

Source

Unknown: Source Unknown

Source Confidence

N/A

Cycle Added

2016

Impairment Rationale

Adverse impacts on plant/animal communities

Data Source

Ambient monitoring: Iowa DNR-lakes

Class HH

Human Health

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 use was assessed (monitored) as "fully supported." The Class BLW use was assessed (evaluated) as “WINOFI” due to nuisance algae (cyanobacteria). All other designated uses were “not assessed.”

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2018-2022	22710001	Mill Creek Lake

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
22710001	6	12 / 4	8.2	9	8.5	1	4	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
22710001	6	Chlorophyll a TSI	12 / 4	15	72	52	NO	Mon	Full
22710001	6	Secchi TSI	12 / 4	39	81	58	NO	Mon	Full
22710001	6	Total Phosphorus TSI	12 / 4	37	88	64	NA	NA	NA
22710001	6	Inorganic suspended solids	12 / 4	0.6	7	2	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
22710001	6	Dissolved Oxygen	12 / 4	4.8	11.2	8.3	1	NA / NA	4	NO	Mon	Full
22710001	6	pH	12 / 4	8.2	9	8.5	1	NA / NA	4	NO	Mon	Full
22710001	6	Temperature	12 / 4	17.8	27.3	24	0	NA / NA	4	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
22710001	6	3	32.88951805	36%	28.78757471	34%	YES	Evaluated	3b

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
22710001	6	Ammonia	12 / 4	0.268	0.04	0.02	0 / 0	NO	Mon	Full

Class HH - No Data

Monitoring and Methods

Assessment Key Dates

5/29/2018

Monitoring Start

9/12/2022

Monitoring End

Methods

200

Physical/Chemical Monitoring

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)