Black Pit Lake is a productive, nutrient-rich eutrophic lake in Cerro Gordo County, Iowa. Water quality is graded D based on 2 sampling years through 2022. Overall water quality is improving over recent sampling years. Compared to the 3 other monitored lakes in Cerro Gordo County, Black Pit Lake ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2022-09-12. Grade methodology: LakeGrade methodology.
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Swimming Safety
Swimming not recommended, poor water quality with high algae risk
Water Quality Grade: D, Poor
Murky, only visible to about 5.6 ft. Chlorophyll-a: 40.9 µg/L. Trophic State Index: 60.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 5.6 ft | D |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 40.9 µg/L | F |
| Trophic State Index (TSI) | 60 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Black Pit Lake
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Fishing Black Pit Lake
Water Quality Trend: ↑ Improving
Based on 3 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.6 m/yr | 3 |
| Chlorophyll-a | ↑ Improving | -15.45 µg/L/yr | 3 |
Water Temperature
Black Pit Lake averages about 73°F at the surface in summer, usually warmest in Jul (about 76°F) and coldest in Jun (about 66°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 9 field readings (2018–2022) via the EPA Water Quality Portal. See the full Black Pit Lake water temperature breakdown →
Location
County Ranking
Ranked #3 of 4 lakes in Cerro Gordo County
Cleaner Lakes Within 30 Miles
Black Pit Lake holds Grade D. 2 nearby lakes hold higher grades.
- ABlue Pit LakeCerro Gordo County · 0.2 mi · Two grade letters higher (D → A)
- BRudd LakeFloyd County · 16.8 mi · Two grade letters higher (D → B)
Nearby Lakes in Cerro Gordo County
Explore Black Pit Lake across LakeGrade
More Iowa Lake Rankings
Other Grade D Lakes in Iowa
Eutrophic Lakes in Iowa
More records, surveys & data sources
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth is a modeled estimate.
Regulated Pollution Sources Nearby
3 EPA-permitted facilities operate within about 5 miles of Black Pit Lake under Clean Water Act (NPDES) discharge permits.
- Golden Grain Energy, LlcMason City · 2 mi away · NPDES IA0078735
- Holcim (Us) Inc.Mason City · 4.8 mi away · NPDES IA0000388
- Amrize Cement Inc. - West QuarryMason City · 4.8 mi away · NPDES IA0071951
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.
Data Sources
Water quality data from the EPA Water Quality Portal
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)
Grading methodology based on Metropolitan Council standards
Most recent sample: 2022-09-12
Monitoring stations: 1