Mariposa Lake
Jasper County, Iowa19 acresView mapDirections
Clarity, phosphorus, and algae sit in the clean band for this region.
↑ up from C at the last regrade
- Eutrophic
- Impaired · Algal growth
- #1 of 2 in the county
Mariposa Lake in Jasper County, Iowa has a water quality grade of B (Good). Water clarity: 5.1 ft visibility. Phosphorus: 31 µg/L. Chlorophyll-a (algae): 8.9 µg/L. Surface area: 18.7 acres.
- Clarity
- 5.1 ft
- Typical in September
- 66°F
- Area
- 19 acres
- Type
- Eutrophic
- Phosphorus
- 31 µg/L
- Chlorophyll-a
- 8.9 µg/L
- Trend
- ↓ Declining
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Watch Mariposa Lake’s letter
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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. Water quality is graded B based on 2 sampling years through 2024. 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. Grade methodology: LakeQuality methodology.
Swimming Safety
Grade onlyLow algae
Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
The B is nutrients and algae, 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.
Water Quality Grade: B (Good)
Murky, only visible to about 5.1 ft. Phosphorus 31 µg/L. Chlorophyll-a 8.9 µg/L. TSI 53. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 5.1 ft | Not graded |
| Phosphorus | 31 µg/L | Good |
| Chlorophyll-a (Algae) | 8.9 µg/L | Good |
| Trophic State Index (TSI) | 53 | Eutrophic |
High nutrients, frequent algae, reduced clarity
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.
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
| Characteristic | Value |
|---|---|
| Surface Area | 19 acres |
No bathymetric survey has been published for Mariposa Lake, so its depth is not documented here.
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 |
| Phosphorus | ↓ Declining | +51.35 µg/L/yr | 4 |
| Chlorophyll-a | ↓ Declining | +8.37 µg/L/yr | 5 |
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
County Ranking
Ranked #1 of 2 lakes in Jasper County
Nearby Lakes in Jasper County
Frequently asked questions about Mariposa Lake
Where is Mariposa Lake?
- Mariposa Lake is a lake in Jasper County, Iowa. LakeQuality grades it B for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Mariposa Lake?
- Mariposa Lake in Jasper County, Iowa has a water quality grade of B (Good). 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?
- The B is nutrients and algae, 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.
Explore Mariposa Lake across LakeQuality
More Iowa Lake Rankings
Other Grade B Lakes in Iowa
Eutrophic Lakes in Iowa
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)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database