Long Lake
Sauk County, WisconsinView mapDirections
Wisconsin DNR publishes the water-quality measurements for Long Lake. Here is what has been measured.
- Eutrophic
- Public access
Long Lake in Sauk County, Wisconsin has water-quality measurements published by Wisconsin DNR, shown here as reported. Water clarity: 4.1 ft visibility. Phosphorus: 27.9 µg/L.
Long Lake is a productive, nutrient-rich eutrophic lake in Sauk County, Wisconsin. Water clarity is declining over recent sampling years. Limited fish-species data available. Public access is available. Compared to the 6 other monitored lakes in Sauk County, Long Lake ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2026-05-27. Methodology: how these readings are compared.
Swimming conditions
Readings onlyModerate 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 Long 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 Long Lake
These are the measurements Wisconsin DNR publishes for Long Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Murky, only visible to about 4.1 ft. Phosphorus 27.9 µg/L. TSI 54.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 4.1ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 27.9µg/L | Fair 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. | 54 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about Long Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Long Lake typically sits around 50°F at the surface in October. Summer average is about 75°F. Usually warmest in Jun (about 79°F) and coldest in Oct (about 50°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (50°F) to its warmest (79°F).
Typical surface water temperature by month, from 34 field readings (2024–2025) via the EPA Water Quality Portal. See the full Long Lake water temperature breakdown →
Stays via Stay22
Stays near Long Lake
Compare lakeside cabins, hotels, and vacation rentals near Long Lake in Sauk 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.
Top-rated places to stay near Long Lake
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Fishing Long Lake
Water Quality Trend: Stable
Based on 5 years of monitoring (2021–2025).
Water clarity
Worsening5 years
Phosphorus
Improving-3.24 µg/L/yr5 years
Nearby Lakes in Sauk County
Frequently asked questions about Long Lake
Where is Long Lake?
- Long Lake is a lake in Sauk County, Wisconsin. Its water-quality measurements are published by Wisconsin DNR and shown on this page as reported.
What is the water quality of Long Lake?
- Long Lake in Sauk County, Wisconsin has water-quality measurements published by Wisconsin DNR, shown here as reported. Water clarity: 4.1 ft visibility. Phosphorus: 27.9 µg/L.
Is Long Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
What is the water temperature of Long Lake?
- Long Lake typically sits around 50°F at the surface in October, from 34 EPA Water Quality Portal field readings (2024–2025). That is a typical value for the month, not a live reading.
Can I fish at Long Lake?
- Public access to Long Lake is listed as yes on the lake record. Seasons, size and bag limits, and whether you need a license are set by Wisconsin's fish and wildlife agency, so check its current regulations before you go.
Explore Long Lake across LakeQuality
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Where this data comes from
84 measurements from 2 monitoring stations, 2021–2026. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Wisconsin Department of Natural Resources
WIDNR_WQX84 samples · 2021–2026
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.