Mariposa Lake is a 19-acre productive, nutrient-rich eutrophic lake in Jasper County, Iowa. Water quality is graded C based on 2 sampling years through 2024. Overall water quality is declining over recent sampling years. Compared to the 7 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. Grade methodology: LakeGrade methodology.
Watch Mariposa Lake water quality
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Swimming Safety
Generally safe for swimming, moderate water quality
Water Quality Grade: C, Fair
Murky, only visible to about 5.1 ft. Chlorophyll-a: 8.9 µg/L. Trophic State Index: 53.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 5.1 ft | D |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 8.9 µg/L | B |
| Trophic State Index (TSI) | 53 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 19 acres |
Where to stay near Mariposa Lake
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Fishing Mariposa Lake
Water Quality Trend: ↓ Declining
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.229 m/yr | 5 |
| Chlorophyll-a | ↓ Declining | +8.37 µg/L/yr | 5 |
Water Temperature
Mariposa Lake averages about 78°F at the surface in summer, usually warmest in Aug (about 78°F) and coldest in Sep (about 66°F). These are typical values by month — not a live reading.
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 →
Location & Depth Map
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.
County Ranking
Ranked #1 of 8 lakes in Jasper County
Nearby Lakes in Jasper County
Explore Mariposa Lake across LakeGrade
More Iowa Lake Rankings
Other Grade C Lakes in Iowa
Eutrophic Lakes in Iowa
More records, surveys & data sources
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
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit IA 03-NSK-867 · Official waterbody report
Data Sources
Water quality data from the EPA Water Quality Portal
Impairment status from EPA ATTAINS 303(d) database
Grading methodology based on Metropolitan Council standards
Most recent sample: 2024-08-25
Monitoring stations: 1