Lake Anna
Florence County, WisconsinLimited DataOligotrophic
Lake Anna earns an A — every scored parameter (clarity) rates among the best monitored waters in Florence County.
The lake's low TSI puts it in oligotrophic territory — the cleanest of the four trophic classes, but also the most vulnerable to nutrient-driven shifts. Lake Anna is unusually deep for Wisconsin at 61 ft, which buffers the lake against summer warming and helps the deep water stay oxygenated. The lake is compact at 33 acres, with partial shoreline records and little volume to buffer nutrient inputs. Among the 39 graded lakes in Florence County, Lake Anna ranks 7 — in the top quartile locally.
Lake Anna has no invasive species recorded in Wisconsin state databases as of 2023, though prevention practices still apply at all access points. 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 2023-06-30. Grade methodology: LakeGrade methodology.
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Swimming Safety
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A, Excellent
Crystal clear, you can see 20.5 ft down. Trophic State Index: 34.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 20.5 ft | A |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 34 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 61 ft |
| Surface Area | 33 acres |
Fish Species
Click a species to see all Wisconsin and Minnesota lakes where it is found.
→ Best fishing times for Lake Anna (14-day solunar calendar)
→ Is it safe to eat fish from Lake Anna? (mercury & PFAS guide)
→ Lake Anna fishing regulations (limits, seasons, special rules)
Water Quality Trend: ↓ Declining
Based on 3 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.251 m/yr | 3 |
Location
County Ranking
Ranked #7 of 39 lakes in Florence County
Nearby Lakes in Florence County
More Wisconsin Lake Rankings
Other Grade A Lakes in Wisconsin
Washington County · Clarity: 11.8 ft
Washington County · Clarity: 12.6 ft
Walworth County · Clarity: 11 ft
Waukesha County · Clarity: 11.3 ft
Walworth County · Clarity: 20.2 ft
Kenosha County · Clarity: 10 ft
Oligotrophic Lakes in Wisconsin
WI DNR Lake Profile
Authoritative data from the Wisconsin DNR LakePages. 1 station on file (most recent sample 2023).
Fish Species (DNR-rated)
Data Sources
Water quality data from the EPA Water Quality Portal
Grading methodology based on Metropolitan Council standards
Most recent sample: 2023-06-30
Monitoring stations: 1