Moon Lake
Barron County, WisconsinLimited DataEutrophic
Moon Lake earns a C — middle-of-the-pack water quality, with one or two parameters dragging the average down from a stronger grade.
At a TSI of 57, Moon Lake reads as eutrophic — nutrient-rich enough that summer algal growth and reduced clarity are expected, not unusual. At only 5 ft deep, Moon Lake is shallow — wind keeps the water column mixed and sediment resuspension drives phosphorus levels harder to manage. At 74 acres, Moon Lake sits below the Wisconsin median: a small water where shoreline activity has an outsized effect on water quality. Among the 37 graded lakes in Barron County, Moon Lake sits at rank 18, above the county median.
An invasive species record — Chinese Mystery Snail — has been logged at Moon Lake; Wisconsin DNR maintains the official infested-waters list. The lake's fish records list 2 species — a varied community without one dominant gamefish. Monitoring depth is thin here: the LakeGrade rubric is applied to a small number of sample years, and the grade will be revised as more data accumulates.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2025-07-30. Grade methodology: LakeGrade methodology.
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Swimming Safety
Generally safe for swimming, moderate water quality
Water Quality Grade: C, Fair
No clarity data. Phosphorus level: 39.9 µg/L. Trophic State Index: 57.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No data | |
| Phosphorus | 39.9 µg/L | C |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 57 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 5 ft |
| Surface Area | 74 acres |
Fish Species
Click a species to see all Wisconsin and Minnesota lakes where it is found.
→ Best fishing times for Moon Lake (14-day solunar calendar)
→ Is it safe to eat fish from Moon Lake? (mercury & PFAS guide)
→ Moon Lake fishing regulations (limits, seasons, special rules)
Invasive & Introduced Species
Red chips are ecologically harmful invasive species. Gray chips are stocked or introduced fish that aren't a current ecological concern.
Water Quality Trend: → Stable
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.186 m/yr | 6 |
| Phosphorus | ↓ Declining | +0.92 µg/L/yr | 6 |
Location
County Ranking
Ranked #18 of 37 lakes in Barron County
Nearby Lakes in Barron County
More Wisconsin Lake Rankings
Other Grade C Lakes in Wisconsin
Eutrophic Lakes in Wisconsin
WI DNR Lake Profile
Authoritative data from the Wisconsin DNR LakePages. Monitored by volunteers since 2013. 1 station on file (most recent sample 2025).
Fish Species (DNR-rated)
DNR Reports & Resources
Wisconsin DNR Fisheries scientists publish multi-year survey reports for Moon Lake covering fish populations, stocking, water quality, and management. 1 report on file.
- 2021Big Moon Lake comprehensive survey, 2021Comprehensive Survey · WI DNR · 2021 (PDF)
EPA Impairment Status
Moon Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5R).
Causes of impairment
Source: EPA ATTAINS assessment unit WI10006654 · 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: 2025-07-30
Monitoring stations: 2