Black Pit Lake
Cerro Gordo County, IowaView mapDirections
Nutrients and algae run well above the regional average.
↓ down from D at the last regrade
- Hypereutrophic
- #3 of 4 in the county
Black Pit Lake in Cerro Gordo County, Iowa has a water quality grade of F (Algae-prone). Water clarity: 5.6 ft visibility. Phosphorus: 55.3 µg/L. Chlorophyll-a (algae): 39.7 µg/L.
- Clarity
- 5.6 ft
- Typical in August
- 76°F
- Type
- Hypereutrophic
- Trend
- ↑ Improving
Stays via Stay22
Stays near Black Pit Lake
Compare lakeside cabins, hotels, and vacation rentals near Black Pit Lake in Cerro Gordo County, Iowa — live availability and prices for your trip. Switch the map to Satellite to see the lake and how close each stay is to the water. The water-quality grade measures nutrients and algae, not lodging — cabins and rentals around Black Pit Lake are listed below.
Top-rated places to stay near Black Pit Lake
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Watch Black Pit Lake’s letter
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Black Pit Lake is a highly nutrient-loaded hypereutrophic lake in Cerro Gordo County, Iowa. Water quality is graded F 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: 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 F is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Water Quality Grade: F (Algae-prone)
Murky, only visible to about 5.6 ft. Phosphorus 55.3 µg/L. Chlorophyll-a 39.7 µg/L. TSI 60. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 5.6 ft | Not graded |
| Phosphorus | 55.3 µg/L | Fair |
| Chlorophyll-a (Algae) | 39.7 µg/L | Poor |
| Trophic State Index (TSI) | 60 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Water Temperature
Black Pit Lake typically sits around 76°F at the surface in August. Summer average is about 73°F. 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 →
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 |
| Phosphorus | ↑ Improving | -20.1 µg/L/yr | 3 |
| Chlorophyll-a | ↑ Improving | -15.75 µg/L/yr | 3 |
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.
County Ranking
Ranked #3 of 4 lakes in Cerro Gordo County
Nearby Lakes With Higher Grades
Black Pit Lake holds Grade F. 3 nearby lakes hold higher nutrient-and-algae grades — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in Cerro Gordo County
Frequently asked questions about Black Pit Lake
Where is Black Pit Lake?
- Black Pit Lake is a lake in Cerro Gordo County, Iowa. LakeQuality grades it F for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Black Pit Lake?
- Black Pit Lake in Cerro Gordo County, Iowa has a water quality grade of F (Algae-prone). Water clarity: 5.6 ft visibility. Phosphorus: 55.3 µg/L. Chlorophyll-a (algae): 39.7 µg/L.
Is Black Pit Lake safe to swim in?
- The F is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
What is the water temperature of Black Pit Lake?
- Black Pit Lake typically sits around 76°F at the surface in August, from 9 EPA Water Quality Portal field readings (2018–2022). That is a typical value for the month, not a live reading.
Explore Black Pit Lake across LakeQuality
More Iowa Lake Rankings
Other Grade F Lakes in Iowa
Hypereutrophic Lakes in Iowa
Where this data comes from
36 measurements from 1 monitoring station, 2020–2022. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Iowa DNR Surface Water Monitoring Data
21IOWA_WQX36 samples · 2020–2022
Analytical methods
- Unknown
- Phosphorus by Colorimetry
- 445.0 ~ EPA; Chlorophyll and Pheophytin in Algae by Fluorescence
- 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)