Mary Lake
Marinette County, WisconsinMesotrophic
On the LakeGrade scale Mary Lake grades a B, with clarity at 9.0 ft and 14 µg/L of phosphorus placing it above the Wisconsin median. Secchi readings are the weakest of the scored parameters, suggesting suspended sediment or algal biomass dominates the optical signal.
The lake sits in the mesotrophic zone — the band where most well-managed Wisconsin lakes fall. A maximum depth of 38 ft puts Mary Lake in the middle of Wisconsin's depth distribution. At 186 acres, Mary Lake fits the Wisconsin median for monitored lakes, with partial shoreline records. Within Marinette County's 21 graded lakes, Mary Lake ranks 12 — below the local median, though not at the bottom.
Eurasian watermilfoil has been documented at Mary Lake, requiring shoreline management to keep dense mats from crowding native vegetation. Bass fishing is part of the appeal: the species list runs to 3, anchored by largemouth and/or smallmouth bass. 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 2023-08-28. Grade methodology: LakeGrade methodology.
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Swimming Safety
Good for swimming, clear water with low algae levels
Water Quality Grade: B, Good
Moderate clarity, visible to about 9 ft. Phosphorus level: 13.5 µg/L. Trophic State Index: 44.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 9 ft | C |
| Phosphorus | 13.5 µg/L | A |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 44 | Mesotrophic |
Moderate nutrients, good water quality
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 38 ft |
| Surface Area | 186 acres |
Fish Species
Click a species to see all Wisconsin and Minnesota lakes where it is found.
→ Best fishing times for Mary Lake (14-day solunar calendar)
→ Is it safe to eat fish from Mary Lake? (mercury & PFAS guide)
→ Mary 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 4 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | +0.075 m/yr | 4 |
| Phosphorus | → Stable | +0.23 µg/L/yr | 4 |
Location
County Ranking
Ranked #12 of 21 lakes in Marinette County
Cleaner Lakes Within 30 Miles
Mary Lake holds Grade B. 2 nearby lakes hold higher grades.
- ABig Newton LakeMarinette County · mi · Higher grade (B → A)
- ALittle Newton LakeMarinette County · mi · Higher grade (B → A)
Nearby Lakes in Marinette County
More Wisconsin Lake Rankings
State Parks Near Mary Lake
Other Grade B Lakes in Wisconsin
Mesotrophic Lakes in Wisconsin
WI DNR Lake Profile
Authoritative data from the Wisconsin DNR LakePages. 2 stations on file (most recent sample 2023).
Fish Species (DNR-rated)
DNR Reports & Resources
Wisconsin DNR Fisheries scientists publish multi-year survey reports for Mary Lake covering fish populations, stocking, water quality, and management. 1 report on file.
- 2020Timms Lake fishery summary, 2020Fisheries Survey · WI DNR · 2020 (PDF)
Data Sources
Water quality data from the EPA Water Quality Portal
Grading methodology based on Metropolitan Council standards
Most recent sample: 2023-08-28
Monitoring stations: 2