Lower Gar Lake IA 06-LSR-1646

Dickinson County S32T99NR36W 2 mi. NE of Milford.

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: 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: Chlorophyll a TSI values are continuing to improve.
Created: 11/1/2023 8:13:32 AM
Updated: 2/5/2024 2:46:43 PM

Use Support

Class A1

Recreation - Primary contact

Fully Supported

Class BLW

Aquatic Life - Lakes and wetlands

WINOFI

Exotic/Invasive Species: Exotic Species

Support Level

Further Investigation Needed

Impairment Code

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

Cause Magnitude

Slight

Status

Continuing

Source

Other: Exotic Species

Source Confidence

High

Cycle Added

2016

Impairment Rationale

Adverse impacts on plant/animal communities

Data Source

Biological monitoring: Iowa DNR Fisheries

Algal Growth: Cyanobacteria

Support Level

Further Investigation Needed

Impairment Code

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

Cause Magnitude

Slight

Status

Continuing

Source

Agriculture

Source Confidence

Low

Cycle Added

2020

Impairment Rationale

Adverse impacts on plant/animal communities

Data Source

Ambient monitoring: Iowa DNR-lakes

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

Natural

Source Confidence

High

Cycle Added

2022

Impairment Rationale

Non Pollutant-caused fish kill

Data Source

Fish kill investigation: Iowa DNR

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 due to an invasive species introduction (Zebra Mussels) and due to cyanobacteria blooms. The Class BLW use was also assessed (evaluated) as “WINOFI” based on the results of a fish kill investigation. All other designated uses were “not assessed.” Note: A TMDL for turbidity at Lower Gar Lake was prepared by DNR and approved by EPA in 2002. Because all Section 303(d) impairments identified for the current assessment/listing cycle [turbidity (algal and inorganic)] are addressed by the TMDL, this waterbody is placed in IR Category 4a.

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	22300012	Lower Gar 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
22300012	6	12 / 4	8.13	8.63	8.42	0	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
22300012	6	Chlorophyll a TSI	15 / 5	48	72	56	NO	Mon	Full
22300012	6	Secchi TSI	15 / 5	50	75	63	NO	Mon	Full
22300012	6	Total Phosphorus TSI	15 / 5	52	76	66	NA	NA	NA
22300012	6	Inorganic suspended solids	15 / 5	0.6	17	4.5	NA	NA	NA

DNR's assessment methodology indicates that a TSI value less than or equal to 63 is necessary to suggest de-listing of an impairment. The Secchi depth TSI value for the 2004 assessment listing cycle was 74, 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 2024 assessment/listing cycle is less than or equal to the delisting threshold of 63 (median TSI value for Secchi depth was 63), based on DNR's methodology, these values suggest "full support" of the Class A1 uses protecting against aesthetically objectionable conditions and the impairment (5a) for Secchi depth is suggested for delisting for the 2024 assessment/listing cycle.

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
22300012	6	Dissolved Oxygen	13 / 5	6.9	12.5	8.9	0	NA / NA	4	NO	Mon	Full
22300012	6	pH	12 / 4	8.13	8.63	8.42	0	NA / NA	4	NO	Mon	Full
22300012	6	Temperature	13 / 5	16	28.1	23.6	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
22300012	6	3	103.2768169	96%	31.57159441	96%	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
22300012	6	Ammonia	12 / 4	0.07	0.02	0.02	0 / 0	NO	Mon	Full

Class BLW - Fish Kill Assessment: The Class BLW aquatic life use assessment based on the 2020 fish kill placed this segment in Category 3b. This assessment was “evaluated” because: (1) the cause of the fish kill was not identified or (2) the fish kill was attributed to a non-pollutant cause (e.g., winterkill). Segments assessed using “evaluated” assessments are placed in Category 3b and are added to the state list of Waters In Need Of Further Investigation (WINOFI). If no additional fish kills are reported in this segment for a 5-year period (2025), the Category will be changed from 3b to 3a (not assessed).

Details about the 2020 fish kill can be found here:https://programs.iowadnr.gov/fishkill/Events/995

Class BLW additional information: This lake was infested with Zebra mussels in 2012 and the population exploded in 2015. This invasive species will likely cause water quality to degrade in the future. This potential impairment is not appropriate for Iowa’s Section 303(d) list of impaired waters (Integrated Report Category 5) but is appropriate for IR Category 3b of Iowa’s Integrated Report and Iowa’s list of waters in need of further investigation.

Class HH - No Data

Monitoring and Methods

Assessment Key Dates

5/29/2018

Monitoring Start

9/11/2022

Monitoring End

5/13/2003

TMDL Completed

6/3/2020

Fish Kill

Methods

120

Surveys of fish and game biologists/other professionals

140

Incidence of spills and/or fish kills

200

Physical/Chemical Monitoring

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)