Stolley Pit Lake
Clay County, IowaView mapDirections
Nutrients and algae sit mid-range for this region.
↑ up from D at the last regrade
- Eutrophic
- #1 of 1 in the county
- Public access
Stolley Pit Lake in Clay County, Iowa has a water quality grade of C (Fair). Water clarity: 2.7 ft visibility. Phosphorus: 48 µg/L. Chlorophyll-a (algae): 17.3 µg/L.
- Clarity
- 2.7 ft
- Type
- Eutrophic
- Phosphorus
- 48 µg/L
- Chlorophyll-a
- 17.3 µg/L
- Trend
- ↓ Declining
- Public access
- Yes
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Watch Stolley Pit Lake’s letter
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Free interactive depth-contour map of Stolley Pit Lake, reaching a maximum surveyed depth of 12 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Iowa DNR.
Stolley Pit Lake is a productive, nutrient-rich eutrophic lake in Clay County, Iowa. Water quality is graded C based on 2 sampling years through 2024. Overall water quality is declining over recent sampling years. Limited fish-species data available. Public access is available.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2024-09-09. Grade methodology: LakeQuality methodology.
Swimming Safety
Grade onlyAlgae risk
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 C is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Water Quality Grade: C (Fair)
Very murky, less than 2.7 ft of visibility. Phosphorus 48 µg/L. Chlorophyll-a 17.3 µg/L. TSI 60. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2.7 ft | Not graded |
| Phosphorus | 48 µg/L | Fair |
| Chlorophyll-a (Algae) | 17.3 µg/L | Fair |
| Trophic State Index (TSI) | 60 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Fishing Stolley Pit Lake
Water Quality Trend: ↓ Declining
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.36 m/yr | 2 |
| Phosphorus | ↓ Declining | +13.5 µg/L/yr | 2 |
| Chlorophyll-a | ↑ Improving | -9.1 µg/L/yr | 2 |
Regulated Pollution Sources Nearby
2 EPA-permitted facilities operate within about 5 miles of Stolley Pit Lake under Clean Water Act (NPDES) discharge permits, including 1 classified by the EPA as major discharger. 2 facilities have a reported Clean Water Act violation in the past three years.
- Spencer, City Of StpSpencer · 3.6 mi away · NPDES IA0021059MajorRecent violation
- Corn Belt Power Cooperative-Wisdom StationSpencer · 3.4 mi away · NPDES IA0004570Recent violation
Facilities permitted to discharge under the Clean Water Act within ~5 miles; proximity does not by itself mean a facility affects this lake. Source: EPA ECHO (ICIS-NPDES), as of 2026-07.
County Ranking
Ranked #1 of 1 lakes in Clay County
Nearby Lakes With Higher Grades
Stolley Pit Lake holds Grade C. One nearby lake has a higher nutrient-and-algae grade — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in Clay County
Frequently asked questions about Stolley Pit Lake
Where is Stolley Pit Lake?
- Stolley Pit Lake is a lake in Clay County, Iowa. LakeQuality grades it C for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Stolley Pit Lake?
- Stolley Pit Lake in Clay County, Iowa has a water quality grade of C (Fair). Water clarity: 2.7 ft visibility. Phosphorus: 48 µg/L. Chlorophyll-a (algae): 17.3 µg/L.
Is Stolley Pit Lake safe to swim in?
- The C is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Explore Stolley Pit Lake across LakeQuality
More Iowa Lake Rankings
Other Grade C Lakes in Iowa
Eutrophic Lakes in Iowa
Where this data comes from
29 measurements from 1 monitoring station, 2023–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Iowa DNR Surface Water Monitoring Data
21IOWA_WQX29 samples · 2023–2024
Analytical methods
- Unknown
- Phosphorus by Colorimetry
- 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
Regulated discharger data from EPA ECHO (ICIS-NPDES)