Pentwater Lake
Oceana County, Michigan485 acresView mapDirections
Not Rated: one monitoring station are on record, but they measured water clarity only. LakeQuality’s A–F method grades total phosphorus, total nitrogen, chlorophyll-a, and turbidity; clarity is shown, not scored.
- Limited data
Pentwater Lake in Oceana County, Michigan is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 6.5 ft visibility. Surface area: 484.7 acres.
- Clarity
- 6.5 ft
- Area
- 485 acres
- Trend
- ↑ Improving
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Watch Pentwater Lake’s letter
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Why Pentwater Lake has no grade
Pentwater Lake has monitoring on record from one station, but only water clarity was measured. LakeQuality’s A–F letter uses total phosphorus, total nitrogen, chlorophyll-a, and turbidity against EPA National Lakes Assessment condition classes. With none of those grading measurements on record, Pentwater Lake is Not Rated — not an F. Its 6.5-foot median from 80 readings collected 2016–2022 is still shown as clarity, but clarity alone cannot earn a letter.
Not Rated is EPA Integrated Reporting Category 3 — insufficient information. Everything below that has been measured is still reported on this page.
Sampling is run by EGLE and volunteer programs, and published through the EPA Water Quality Portal. Read the full grading methodology.
Pentwater Lake is a 485-acre lake in Oceana County, Michigan. Overall water quality is improving over recent sampling years. The lake supports 1 documented fish species including Brown trout.
Source: EPA Water Quality Portal sampling records, EGLE, last sampled 2022-09-30. Grade methodology: LakeQuality methodology.
Swimming Safety
Not ratedLimited data
The letter is not a swimming clearance. Check local advisories before you swim.
Water quality measurements for Pentwater Lake
These readings exist but are not enough for an A–F grade — see why.
Murky, only visible to about 6.5 ft. TSI 50.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 6.5 ft | Not graded |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 50 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 485 acres |
No bathymetric survey has been published for Pentwater Lake, so its depth is not documented here.
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Pentwater Lake
Water Quality Trend: ↑ Improving
Based on 8 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.532 m/yr | 8 |
| Phosphorus | ↑ Improving | -0.71 µg/L/yr | 6 |
| Chlorophyll-a | ↓ Declining | +0.79 µg/L/yr | 7 |
Regulated Pollution Sources Nearby
2 EPA-permitted facilities operate within about 5 miles of Pentwater Lake under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Pentwater CwpPentwater · 0.7 mi away · NPDES MI0058875Recent violation
- Blarney Castle OilHart · 3.4 mi away · NPDES MIG080727
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.
Graded lakes near Pentwater Lake
Pentwater Lake has no grade, but these lakes within a short drive do.
Nearby Lakes in Oceana County
Frequently asked questions about Pentwater Lake
Where is Pentwater Lake?
- Pentwater Lake is a lake in Oceana County, Michigan. LakeQuality has not rated this lake (UNRATED) — the only measurement available is water clarity, which is not a water-quality indicator on its own — EPA's National Lakes Assessment does not grade clarity.
What is the water quality grade for Pentwater Lake?
- Pentwater Lake in Oceana County, Michigan is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 6.5 ft visibility. Surface area: 484.7 acres.
Is Pentwater Lake safe to swim in?
- The letter is not a swimming clearance. Check local advisories before you swim.
What fish are in Pentwater Lake?
- Fish species found in Pentwater Lake include Brown trout. Pentwater Lake is located in Oceana County, Michigan.
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Where this data comes from
80 measurements from 1 monitoring station, 2016–2022. Retrieved from the EPA Water Quality Portal on 2026-08-26.
Collected and reported by
- North American Lake Management Society
NALMS80 samples · 2016–2022
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)