Windmill Lake IA 05-PLA-1482

Taylor County S36T69NR35W 4 mi E of New Market.

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: 4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
Trophic: Eutrophic
Trend: Stable
Created: 1/3/2022 8:06:20 AM
Updated: 1/27/2022 11:14:45 AM

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

Agriculture

Source Confidence

Moderate

Cycle Added

2006

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

TMDL monitoring: Iowa DNR

Class BLW

Aquatic Life - Lakes and wetlands

Fully Supported

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 “not supported” due to poor water transparency caused by non-algal turbidity that violates Iowa’s narrative water quality standard protecting against aesthetically objectionable conditions. The Class BLW use was assessed (monitored) as “fully supported." All other designated uses were “not assessed.” NOTE: A TMDL for impairments at Windmill Lake due to algae and Turbidity was prepared by Iowa DNR and approved by the U.S. EPA in 2018. Because all Section 303(d) impairments identified for the current assessment/listing cycle (turbidity) are addressed by the TMDL, this waterbody is placed in IR Category 4a (impaired; TMDL approved).

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2016-2019	22870003	Windmill 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
22870003	6	12 / 4	7.4	8.9	8.2	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
22870003	6	Chlorophyll a TSI	12 / 4	36	71	58	NO	Monitored	Full
22870003	6	Secchi TSI	12 / 4	67	87	73	YES	Monitored	Not
22870003	6	Total Phosphorus TSI	12 / 4	63	79	70	NA	NA	NA
22870003	6	Inorganic suspended solids	12 / 4	0.3	29	9.8	NA	NA	NA

DNR's assessment methodology indicates that at least two assessment/listing cycles with a TSI value less than or equal to 63 are necessary to suggest the de-listing of an impairment. The chlorophyll a TSI value for the 2004 assessment listing cycle was 70, which based on DNR's assessment/listing methodology indicated an impairment based on the narrative criteria protecting against aesthetically objectionable conditions. Because the TSI value for the 2020 assessment/listing cycle was less than the trigger of 65 (2020 listing for chlorophyll a was 62) and because the TSI value for the current listing cycle is 58, based on DNR's methodology, these values suggest "full support" of the Class A1 use protecting against aesthetically objectionable conditions and the impairment (5a) for chlorophyll a is suggested for delisting 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
22870003	6	Ammonia	12 / 4	0.0003	0.181	0.07	NA	0 / 0	4	NO	Monitored	Full
22870003	6	Dissolved Oxygen	12 / 4	4.4	12.1	7.6	1	NA / NA	4	NO	Monitored	Full
22870003	6	pH	12 / 4	7.4	8.9	8.2	0	NA / NA	4	NO	Monitored	Full
22870003	6	Temperature	12 / 4	20	30.6	25.1	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
22870003	6	6	113.63	98.3%	7.28	77.4%	NO	Evaluated	NA

Class: No Data

Monitoring and Methods

Assessment Key Dates

6/15/2016

Non-fixed Monitoring Start Date

9/9/2019

Non-fixed Monitoring End Date

6/26/2018

TMDL Completed

Methods

120

Surveys of fish and game biologists/other professionals

222

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

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)