Mark Twain Lake
Monroe County, WisconsinEutrophic
Mark Twain Lake is a productive, nutrient-rich eutrophic lake in Monroe County, MO. Water quality is graded C based on 3 sampling years through 2024. Compared to the 2 other monitored lakes in Monroe County, Mark Twain Lake ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, local state DNR records, last sampled 2024-08-31. Grade methodology: LakeGrade methodology.
Swimming Safety
Generally safe for swimming, moderate water quality
Water Quality Grade: C, Fair
Murky, only visible to about 3.8 ft. Phosphorus level: 36 µg/L. Chlorophyll-a: 11.9 µg/L. Trophic State Index: 56.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3.8 ft | D |
| Phosphorus | 36 µg/L | C |
| Chlorophyll-a (Algae) | 11.9 µg/L | C |
| Trophic State Index (TSI) | 56 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Location
County Ranking
Ranked #2 of 3 lakes in Monroe County
Cleaner Lakes Within 30 Miles
Mark Twain Lake holds Grade C. One nearby lake has a higher grade.
See full comparison →Nearby Lakes in Monroe County
More Wisconsin Lake Rankings
Other Grade C Lakes in Wisconsin
Warren County · Clarity: 3.8 ft
Ralls County · Clarity: 3.7 ft
Warren County · Clarity: 3.3 ft
Platte County · Clarity: 4.7 ft
Barry County · Clarity: 5 ft
Phelps County · Clarity: 4.9 ft
Eutrophic Lakes in Wisconsin
EPA Impairment Status
Mark Twain Lake is officially listed as impaired under Clean Water Act §303(d) in the 2022 EPA reporting cycle (IR category 5).
Causes of impairment
Source: EPA ATTAINS assessment unit MO_7033.00 · 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: 2024-08-31
Monitoring stations: 1