Mirror Lake
Sauk County, Wisconsin137 acresView mapDirections
Wisconsin DNR publishes the water-quality measurements for Mirror Lake. Here is what has been measured.
- Eutrophic
- Public access
Mirror Lake in Sauk County, Wisconsin has water-quality measurements published by Wisconsin DNR, shown here as reported. Water clarity: 4.6 ft visibility. Phosphorus: 65.4 µg/L. Surface area: 137 acres.
Mirror Lake is a 137-acre productive, nutrient-rich eutrophic lake in Sauk County, Wisconsin. Water clarity is improving over recent sampling years. Limited fish-species data available. Public access is available. Compared to the 6 other monitored lakes in Sauk County, Mirror Lake ranks #6 for water quality.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2025-08-02. Methodology: how these readings are compared.
Mirror Lake covers about 140 acres in Sauk County. If you are planning to stay, you can search lake houses and cabins around Mirror Lake on Vrbo, or look for a hotel room near the lake on Booking.com or Expedia.
Swimming conditions
Readings onlyBacteria tested: exceedances
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.
Based on E. coli testing, Mirror Lake occasionally exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 5.4% of 112 samples across 8 seasons.
This is a historical summary of past testing, not a current condition — bacteria levels change quickly, especially after rain. Always check Wisconsin’s current beach and health-department advisories before swimming.
Whether Mirror 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 Mirror Lake
These are the measurements Wisconsin DNR publishes for Mirror 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 4.6 ft. Phosphorus 65.4 µg/L. TSI 60.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 4.6ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 65.4µg/L | Poor 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. | 60 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about Mirror Lake
Answers come straight from the public measurements and survey records on this page.
Lake Details
Surface area
137 acres
Public access
Yes
Listed by Wisconsin DNR
No bathymetric survey has been published for Mirror Lake, so its depth is not documented here.
Stays via Stay22
Stays near Mirror Lake
Compare lakeside cabins, hotels, and vacation rentals near Mirror 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. The water-quality readings cover nutrients and algae, not lodging. Cabins and rentals around Mirror Lake are listed below.
Top-rated places to stay near Mirror Lake
Prices for Oct 16–18, 4 adults. Change dates on the map below.
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
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Fishing Mirror Lake
Water Quality Trend: Stable
Based on 6 years of monitoring (2020–2025).
Water clarity
Improving5 years
Phosphorus
Worsening+5.7 µg/L/yr6 years
Reservoir Info (USACE NID)
Mirror Lake is a man-made reservoir impounded by the Delton (completed 1931), built primarily for recreation on the DELL CREEK; gravity-type dam, 19 ft tall and 150 ft long.
- Surface area
- 137 ac
- Normal storage
- 870 ac-ft
- Max storage
- 1,280 ac-ft
- Drainage area
- 71 sq mi
- Hazard class
- Low
- Owner
- Sauk County
Source: USACE National Inventory of Dams, NID ID WI00190 · Operator website
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Mirror Lake under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Christmas Mountain Sanitary District WwtfDellona · 3.5 mi away · NPDES WI0036064Recent violation
Facilities permitted to discharge under the Clean Water Act within ~5 miles; proximity does not by itself mean a facility affects this lake. Source: EPA ECHO (ICIS-NPDES), as of 2026-07.
Nearby Lakes in Sauk County
Frequently asked questions about Mirror Lake
Where is Mirror Lake?
- Mirror 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 Mirror Lake?
- Mirror Lake in Sauk County, Wisconsin has water-quality measurements published by Wisconsin DNR, shown here as reported. Water clarity: 4.6 ft visibility. Phosphorus: 65.4 µg/L. Surface area: 137 acres.
Is Mirror Lake safe to swim in?
- Based on E. coli testing, Mirror Lake occasionally exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 5.4% of 112 samples across 8 seasons. That is a historical summary of past bacteria testing, not a current reading and not a swimming clearance. Bacteria levels can spike quickly after heavy rain, so whether Mirror Lake is safe to swim in today is a call for Wisconsin's water agency and the county health department; check their current beach advisories before you swim.
Can I fish at Mirror Lake?
- Public access to Mirror 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 Mirror Lake across LakeQuality
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Where this data comes from
43 measurements from 2 monitoring stations, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Wisconsin Department of Natural Resources
WIDNR_WQX43 samples · 2020–2025
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.
Other records on this page
Regulated discharger data from EPA ECHO (ICIS-NPDES)