Mariposa Lake IA 03-NSK-867

Jasper County S32T81NR18W 6 mi. NE of Newton.

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.

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Cycle: 2024
Release Status: Final
Overall IR: 4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
Trophic: Hypereutrophic
Trend: Stable
Created: 11/1/2023 8:12:55 AM
Updated: 2/2/2024 2:48:11 PM

Use Support

Class A1

Recreation - Primary contact

Not Supported

Algal Growth: Chlorophyll a

Support Level

Not Supported

Impairment Code

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

Cause Magnitude

High

Status

Continuing

Source

Agriculture

Source Confidence

Moderate

Cycle Added

1998

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

Turbidity

Support Level

Not Supported

Impairment Code

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

Cause Magnitude

High

Status

Continuing

Source

Agriculture

Source Confidence

Moderate

Cycle Added

2004

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

Algal Growth: Noxious Aquatic Plants - Algae

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

2004

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

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 aesthetically objectionable conditions caused by poor water transparency and nuisance algae blooms. The Class BLW use was assessed as “fully supported.” Sedimentation remains a concern at this lake. All other designated uses were “not assessed.” Note: A TMDL for algae and turbidity at Mariposa Lake was prepared by DNR and approved by EPA in 2004; thus, this waterbody was placed into IR Category 4a (TMDL approved) for the 2004 assessment/listing cycle. Because all Section 303(d) impairments identified for the current assessment/listing cycle (algal growth and turbidity) are addressed by the TMDL, this waterbody remains 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 2020-2022	22500002	Mariposa 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
22500002	6	8 / 3	8.1	8.8	8.3	0	3	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
22500002	6	Chlorophyll a TSI	8 / 3	46	71	50	NO	Evaluated	Full
22500002	6	Secchi TSI	8 / 3	49	60	52	NO	Evaluated	Full
22500002	6	Total Phosphorus TSI	8 / 3	37	58	50	NA	NA	NA
22500002	6	Inorganic suspended solids	8 / 3	0.7	6	1.9	NA	NA	NA

Although the index value for Chlorophyll a was below the impairment threshold of 65 for this assessment cycle, the Class A1 use of Mariposa Lake 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 one monitored assessment/listing cycle before a lake can be removed from the state's Section 303(d) list (IR Category 5). Therefore, Mariposa Lake will remain listed as "not supported" for the current assessment/listing cycledue to the evaluated assessment.

Although the index value for Secchi is below the impairment threshold of 65 for this assessment cycle, the Class A1 use of Mariposa Lake remains "not supported" due to aesthetically objectionable conditions. Based on DNR's methodology, the median TSI value for Secchi must be 63 or less for onemonitoredassessment/listing cycle before a lake can be removed from the state's Section 303(d) list (IR Category 5). Therefore, Mariposa Lake will remain listed as "not supported" for the current assessment/listing cycle due to the evaluated assessment.

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
22500002	6	Dissolved Oxygen	8 / 3	6.5	10.1	8.7	0	NA / NA	3	NO	Mon	Full
22500002	6	pH	8 / 3	8.1	8.8	8.3	0	NA / NA	3	NO	Mon	Full
22500002	6	Temperature	8 / 3	18.4	27.7	24.2	0	NA / NA	3	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
22500002	6	3	1.066121114	60%	0.036667092	7%	NO	Evaluated	NA

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
22500002	6	Ammonia	8 / 3	0.051	0.02	0.02	0 / 0	NO	Evaluated	Full

Class HH - No Data

Monitoring and Methods

Assessment Key Dates

8/3/2020

Monitoring Start

9/28/2022

Monitoring End

12/14/2004

TMDL Completed

Methods

200

Physical/Chemical Monitoring

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)