Frog Lake
Frog Lake in Florence County, Wisconsin has a water quality grade of B (Good). Water clarity: 9.5 ft visibility. Phosphorus: 16.2 µg/L.
- Clarity
- 9.5 ft
- Type
- Mesotrophic
- Trend
- ↑ Improving
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Frog Lake is a mesotrophic lake in Florence County, Wisconsin. Water quality is graded B based on 1 sampling years through 2026. Overall water quality is improving over recent sampling years. Compared to the 11 other monitored lakes in Florence County, Frog Lake ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2026-06-17. Grade methodology: LakeQuality methodology.
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Swimming Safety
Grade onlyLow algae
Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Good for swimming, clear water with low algae levels
Water Quality Grade: B (Good)
Moderate clarity, visible to about 9.5 ft. Phosphorus level: 16.2 µg/L. Trophic State Index: 44.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 9.5 ft | Not graded |
| Phosphorus | 16.2 µg/L | Good |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 44 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Frog Lake
Compare lakeside cabins, hotels, and vacation rentals near Frog Lake in Florence County, Wisconsin — live availability and prices for your trip. Switch the map to Satellite to see the lake and how close each stay is to the water.
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Fishing Frog Lake
Water Quality Trend: ↑ Improving
Based on 7 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.357 m/yr | 6 |
| Phosphorus | → Stable | +0.11 µg/L/yr | 7 |
County Ranking
Ranked #3 of 12 lakes in Florence County
Nearby Lakes in Florence County
Frequently asked questions about Frog Lake
Where is Frog Lake?
- Frog Lake is a lake in Florence County, Wisconsin. LakeQuality grades it B for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Frog Lake?
- Frog Lake in Florence County, Wisconsin has a water quality grade of B (Good). Water clarity: 9.5 ft visibility. Phosphorus: 16.2 µg/L.
Is Frog Lake safe to swim in?
- Good for swimming, clear water with low algae levels. Frog Lake has a water quality grade of B (Good). Always check local health department advisories before swimming.
Explore Frog Lake across LakeQuality
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Moderate nutrients, good water quality
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Other Grade B Lakes in Wisconsin
Mesotrophic Lakes in Wisconsin
Where this data comes from
51 measurements from 2 monitoring stations, 2020–2026. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Wisconsin Department of Natural Resources
WIDNR_WQX51 samples · 2020–2026
Analytical methods
- Phosphorus by Colorimetry
Monitoring station identifiers (2)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated and data sources.