Thumb Lake
Charlevoix County, Michigan508 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.
- Impaired · Mercury
- 152 ft max depth
- Public access
- Limited data
Thumb Lake in Charlevoix County, Michigan is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 17 ft visibility. Maximum depth: 152 ft. Surface area: 507.5 acres.
- Clarity
- 17 ft
- Max depth
- 152 ft
- Area
- 508 acres
- Public access
- Yes
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Watch Thumb Lake’s letter
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Free interactive depth-contour map of Thumb Lake, reaching a maximum surveyed depth of 152 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Michigan DNR.
Why Thumb Lake has no grade
Thumb 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, Thumb Lake is Not Rated — not an F. Its 17-foot median from 13 readings collected 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.
Thumb Lake is a 508-acre lake in Charlevoix County, Michigan with a maximum depth of 152 feet. The lake supports 3 documented fish species including Blacknose shiner, Rock bass, and Smallmouth bass. Public access is available with 1 public boat landing.
Source: EPA Water Quality Portal sampling records, EGLE, last sampled 2022-08-26. Grade methodology: LakeQuality methodology.
What Thumb Lake is good for
From access and monitoring records, not editorial picks.
- Clear water17 ft of visibility
- Boat launch1 documented ramp
- Fishing3 species recorded
- Deep water152 ft surveyed max depth
Swimming Safety
Not ratedLimited data
The letter is not a swimming clearance. Thumb Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury. Check local advisories before you swim.
Water quality measurements for Thumb Lake
These readings exist but are not enough for an A–F grade — see why.
Crystal clear, you can see 17 ft down. TSI 36.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 17 ft | Not graded |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 36 | Oligotrophic |
Low nutrients, clear water. The letter is not a swimming clearance.
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 152 ft |
| Surface Area | 508 acres |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Thumb LakePublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Thumb Lake
EPA Impairment Status
Thumb Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit MI040700040103-04 · Official waterbody report
Graded lakes near Thumb Lake
Thumb Lake has no grade, but these lakes within a short drive do.
Nearby Lakes in Charlevoix County
Frequently asked questions about Thumb Lake
Where is Thumb Lake?
- Thumb Lake is a lake in Charlevoix 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 Thumb Lake?
- Thumb Lake in Charlevoix County, Michigan is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 17 ft visibility. Maximum depth: 152 ft. Surface area: 507.5 acres.
Is Thumb Lake safe to swim in?
- The letter is not a swimming clearance. Thumb Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury. Check local advisories before you swim.
How deep is Thumb Lake?
- Thumb Lake has a maximum depth of 152 feet. The lake covers 507.5 acres.
What fish are in Thumb Lake?
- Fish species found in Thumb Lake include Blacknose shiner, Rock bass, Smallmouth bass. Thumb Lake is located in Charlevoix County, Michigan.
Are there boat ramps on Thumb Lake?
- Thumb Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Thumb Lake. Public access is listed as yes.
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Where this data comes from
13 measurements from 1 monitoring station, 2022. Retrieved from the EPA Water Quality Portal on 2026-08-26.
Collected and reported by
- North American Lake Management Society
NALMS13 samples · 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
Impairment status from EPA ATTAINS 303(d) database
Lake size & watershed from HydroLAKES (HydroSHEDS)
Named boat-access points from the USGS National Boat Ramps inventory