Thumb Lake
Charlevoix County, WisconsinLimited DataOligotrophic
Thumb Lake is a cold, clear oligotrophic lake in Charlevoix County, MI. Water quality is graded A based on 1 sampling years through 2022. The lake supports 3 documented fish species including Blacknose shiner, Rock bass, and Smallmouth bass. Compared to the 18 other monitored lakes in Charlevoix County, Thumb Lake ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, local state DNR records, last sampled 2022-08-26. Grade methodology: LakeGrade methodology.
Swimming Safety
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A, Excellent
Crystal clear, you can see 17 ft down. Trophic State Index: 36.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 17 ft | A |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 36 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Fish Species
Click a species to see all Wisconsin and Minnesota lakes where it is found.
→ Best fishing times for Thumb Lake (14-day solunar calendar)
→ Is it safe to eat fish from Thumb Lake? (mercury & PFAS guide)
→ Thumb Lake fishing regulations (limits, seasons, special rules)
Location
County Ranking
Ranked #3 of 19 lakes in Charlevoix County
Nearby Lakes in Charlevoix County
More Wisconsin Lake Rankings
Other Grade A Lakes in Wisconsin
Mecosta County · Clarity: 12.8 ft
Benzie County · Clarity: 13.5 ft
Clare County · Clarity: 15 ft
Kalkaska County · Clarity: 16 ft
Gogebic County · Clarity: 18 ft
Iron County · Clarity: 16 ft
Oligotrophic Lakes in Wisconsin
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
Data Sources
Water quality data from the EPA Water Quality Portal
Impairment status from EPA ATTAINS 303(d) database
Grading methodology based on Metropolitan Council standards
Most recent sample: 2022-08-26
Monitoring stations: 1