Frog Lake
Florence County, WisconsinView mapDirections
Wisconsin DNR publishes the water-quality measurements for Frog Lake. Here is what has been measured.
- Mesotrophic
Frog Lake in Florence County, Wisconsin has water-quality measurements published by Wisconsin DNR, shown here as reported. Water clarity: 9.5 ft visibility. Phosphorus: 16.2 µg/L.
Frog Lake is a mesotrophic lake in Florence County, Wisconsin. 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. Methodology: how these readings are compared.
Swimming conditions
Readings onlyLow algae
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether Frog Lake is safe to swim in today is a call for the Wisconsin Department of Natural Resources and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Frog Lake
These are the measurements Wisconsin DNR publishes for Frog Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Moderate clarity, visible to about 9.5 ft. Phosphorus 16.2 µg/L. TSI 44.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 9.5ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 16.2µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | No reading The green pigment in algae — a direct measure of how much algae is in the water. | |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 44 | Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Moderate nutrients, good water quality
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Fishing Frog Lake
Water Quality Trend: Improving
Based on 7 years of monitoring (2020–2026).
Water clarity
Improving6 years
Phosphorus
Stable+0.11 µg/L/yr7 years
Nearby Lakes in Florence County
Frequently asked questions about Frog Lake
Where is Frog Lake?
- Frog Lake is a lake in Florence County, Wisconsin. Its water-quality measurements are published by Wisconsin DNR and shown on this page as reported.
What is the water quality of Frog Lake?
- Frog Lake in Florence County, Wisconsin has water-quality measurements published by Wisconsin DNR, shown here as reported. Water clarity: 9.5 ft visibility. Phosphorus: 16.2 µg/L.
Is Frog Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Explore Frog Lake across LakeQuality
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Fish species and best lakes in Florence County
Species activity outlook by water temperature and season
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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)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.