Mariposa Lake IA 03-NSK-867

Jasper County S32T81NR18W 6 mi. NE of Newton.

This is a DRAFT assessment

Draft assessments may change without notice

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 2022 - 2024
Stream/River Water Quality Data	CY 2022 - 2024
Lake Water Quality Data	CY 2020 - 2024
Biological Sampling Data	CY 2020 - 2024*
Fish Kill Data	CY 2020 - 2024
Fish Tissue Sampling Data	CY 2020 - 2024
Continuous Dissolved Oxygen Sampling Data	CY 2020 - 2024
*Biological sites sampled in both 2019 and 2023 were also assessed.

Open Segment Map
View 2026 assessment summary page

Cycle: 2026
Current Phase: Public Comment
Overall IR: 1 - All designated uses are met.
Trophic: Eutrophic
Trend: Improving
Trend Comment: Median TSI's have decreased from 70's for the 2018 IR to low 50's for the 2026 IR.
Created: 10/27/2025 3:09:42 PM
Updated: 11/17/2025 10:16:53 AM

Use Support

Class A1

Recreation - Primary contact

Fully Supported

Class BLW

Aquatic Life - Lakes and wetlands

Fully Supported

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 “fully supported.” The Class BLW use was assessed as “fully supported.” The Class HH use was assessed (monitored) as "fully supported" based on fish tissue monitoring. 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 2020-2024	22500002	Mariposa Lake
Iowa DNR	6	FT	See Below	1314	Mariposa Lake	Mariposa County Park

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	14 / 5	7.6	9.6	8.4	1	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
22500002	6	Chlorophyll a TSI	14 / 5	44	71	52	NO	MONITORED	FULL
22500002	6	Secchi TSI	14 / 5	49	97	54	NO	MONITORED	FULL
22500002	6	Total Phosphorus TSI	14 / 5	37	96	51	NA	NA	NA
22500002	6	Fixed suspended solids	14 / 5	0.7	61	3	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
22500002	6	Dissolved Oxygen	14 / 5	6.3	10.1	8.5	0	NA / NA	4	NO	MONITORED	FULL
22500002	6	pH	14 / 5	7.6	9.6	8.4	1	NA / NA	4	NO	MONITORED	FULL
22500002	6	Temperature	14 / 5	18.2	27.7	23.9	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
22500002	6	6	87.633	99.96%	0.5514	33.37%	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	14 / 5	0.324	0.04	0.02	0 / 0	NO	MONITORED	FULL

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)
1314	fillet	2024	channel catfish	3	49.3	0.098	<0.0499	<0.0246
Support Level	Full

Monitoring and Methods

Assessment Key Dates

8/3/2020

Monitoring Start

8/26/2024

Monitoring End

12/14/2004

TMDL Completed

Methods

200

Physical/Chemical Monitoring

260

Fish tissue analysis

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)