Mariposa Lake
Jasper County, Iowa19 acresView mapDirections
Iowa DNR publishes the water-quality measurements for Mariposa Lake. Here is what has been measured.
- Eutrophic
- Impaired · Algal growth
Mariposa Lake in Jasper County, Iowa has water-quality measurements published by Iowa DNR, shown here as reported. Water clarity: 5.1 ft visibility. Phosphorus: 31 µg/L. Chlorophyll-a (algae): 8.9 µg/L. Surface area: 18.7 acres.
Free interactive depth-contour map of Mariposa Lake, reaching a maximum surveyed depth of 18 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Iowa DNR.
Mariposa Lake is a 19-acre productive, nutrient-rich eutrophic lake in Jasper County, Iowa. Overall water quality is declining over recent sampling years. Compared to the 1 other monitored lakes in Jasper County, Mariposa Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2024-08-25. Methodology: how these readings are compared.
Swimming conditions
Readings onlyRecreation use not supported
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. Mariposa Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for algal growth, turbidity. Check local advisories before you swim.
Whether Mariposa Lake is safe to swim in today is a call for the Iowa Department of Natural Resources and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Mariposa Lake
These are the measurements Iowa DNR publishes for Mariposa Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Murky, only visible to about 5.1 ft. Phosphorus 31 µg/L. Chlorophyll-a 8.9 µg/L. TSI 53.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 5.1ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 31µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 8.9µg/L | Good GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 53 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about Mariposa Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Mariposa Lake typically sits around 66°F at the surface in September. Summer average is about 78°F. Usually warmest in Aug (about 78°F) and coldest in Sep (about 66°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (66°F) to its warmest (78°F).
Typical surface water temperature by month, from 25 field readings (2010–2023) via the EPA Water Quality Portal. See the full Mariposa Lake water temperature breakdown →
Lake Details
Surface area
19 acres
No bathymetric survey has been published for Mariposa Lake, so its depth is not documented here.
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Fishing Mariposa Lake
Water Quality Trend: Worsening
Based on 5 years of monitoring (2020–2024).
Water clarity
Worsening5 years
Phosphorus
Worsening+51.35 µg/L/yr4 years
Chlorophyll-a
Worsening+8.37 µg/L/yr5 years
Reservoir Info (USACE NID)
Mariposa Lake is a man-made reservoir impounded by the Mariposa Lake Dam (completed 1952), built primarily for recreation on the TR-ALLOWAY CREEK; earth-type dam, 25 ft tall and 525 ft long.
- Surface area
- 18.7 ac
- Normal storage
- 112 ac-ft
- Max storage
- 188 ac-ft
- Drainage area
- 0.92 sq mi
- Hazard class
- Low
- Owner
- Jasper County Conservation Board
Source: USACE National Inventory of Dams, NID ID IA01348 · Operator website
EPA Impairment Status
Mariposa Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).
Causes of impairment
Designated uses not supporting: Recreation.
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit IA 03-NSK-867 · Official waterbody report
Nearby Lakes in Jasper County
Frequently asked questions about Mariposa Lake
Where is Mariposa Lake?
- Mariposa Lake is a lake in Jasper County, Iowa. Its water-quality measurements are published by Iowa DNR and shown on this page as reported.
What is the water quality of Mariposa Lake?
- Mariposa Lake in Jasper County, Iowa has water-quality measurements published by Iowa DNR, shown here as reported. Water clarity: 5.1 ft visibility. Phosphorus: 31 µg/L. Chlorophyll-a (algae): 8.9 µg/L. Surface area: 18.7 acres.
Is Mariposa Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Mariposa Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for algal growth, turbidity. Check local advisories before you swim.
What is the water temperature of Mariposa Lake?
- Mariposa Lake typically sits around 66°F at the surface in September, from 25 EPA Water Quality Portal field readings (2010–2023). That is a typical value for the month, not a live reading.
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Where this data comes from
59 measurements from 1 monitoring station, 2020–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Iowa DNR Surface Water Monitoring Data
21IOWA_WQX59 samples · 2020–2024
Analytical methods
- Unknown
- Phosphorus by Colorimetry
- 445.0 ~ EPA; Chlorophyll and Pheophytin in Algae by Fluorescence
- In-Vitro Determination of Chlorophyll
- ISU modification of APHA 2130-B
Monitoring station identifiers (1)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database