Clear Lake
Clear Lake in Rock County, Wisconsin has a water quality grade of C (Fair). Water clarity: 2.8 ft visibility. Phosphorus: 38.5 µg/L. Maximum depth: 12 ft. Surface area: 77 acres.
- Clarity
- 2.8 ft
- Typical in August
- 80°F
- Max depth
- 12 ft
- Area
- 77 acres
- Type
- Eutrophic
- Trend
- ↓ Declining
- Public access
- Yes
Next lake in Rock County
Clear Lake is a 77-acre productive, nutrient-rich eutrophic lake in Rock County, Wisconsin with a maximum depth of 12 feet. Water quality is graded C based on 1 sampling years through 2025. Overall water quality is declining over recent sampling years. The lake supports 3 documented fish species including Panfish, Largemouth Bass, and Northern Pike. Public access is available with 1 public boat landing. Compared to the 1 other monitored lakes in Rock County, Clear Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2025-09-01. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyModerate
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.
Generally safe for swimming, moderate water quality
Water Quality Grade: C (Fair)
Very murky, less than 2.8 ft of visibility. Phosphorus level: 38.5 µg/L. Trophic State Index: 60.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2.8 ft | Not graded |
| Phosphorus | 38.5 µg/L | Fair |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 60 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Clear Lake
Compare lakeside cabins, hotels, and vacation rentals near Clear Lake in Rock 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 Clear Lake
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Planning a whole trip? See where to stay at Wisconsin’s top lakes →
Water Temperature
Clear Lake typically sits around 80°F at the surface in August. Summer average is about 80°F. Usually warmest in Jul (about 81°F) and coldest in Jun (about 78°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 8 field readings (2024–2025) via the EPA Water Quality Portal.
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 12 ft |
| Surface Area | 77 acres |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Clear LakePublic
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Clear Lake
Invasive & Introduced Species
Red chips are ecologically harmful invasive species. Gray chips are stocked or introduced fish that aren't a current ecological concern.
WI DNR Lake Profile
Authoritative data from the Wisconsin DNR LakePages. Monitored by volunteers since 1990. 1 station on file (most recent sample 2025).
Fish Species (DNR-rated)
Water Quality Trend: ↓ Declining
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -1.85 m/yr | 5 |
| Phosphorus | ↓ Declining | +7.31 µg/L/yr | 5 |
EPA Impairment Status
Clear Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
Source: EPA ATTAINS assessment unit WI10001485 · Official waterbody report
Regulated Pollution Sources Nearby
2 EPA-permitted facilities operate within about 5 miles of Clear Lake under Clean Water Act (NPDES) discharge permits. 2 facilities have a reported Clean Water Act violation in the past three years.
- Consolidated Koshkonong Sanitary Dist WwtfFulton · 2.7 mi away · NPDES WI0021059Recent violation
- Edgerton Wastewater Treatment FacilityEdgerton · 3.6 mi away · NPDES WI0020346Recent 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.
County Ranking
Ranked #1 of 2 lakes in Rock County
Nearby Lakes With Higher Grades
Clear Lake holds Grade C. 2 nearby lakes hold higher nutrient-and-algae grades — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in Rock County
Frequently asked questions about Clear Lake
What is the water quality grade for Clear Lake?
- Clear Lake in Rock County, Wisconsin has a water quality grade of C (Fair). Water clarity: 2.8 ft visibility. Phosphorus: 38.5 µg/L. Maximum depth: 12 ft. Surface area: 77 acres.
Is Clear Lake safe to swim in?
- Generally safe for swimming, moderate water quality. Clear Lake has a water quality grade of C (Fair). Always check local health department advisories before swimming.
What is the water temperature of Clear Lake?
- Clear Lake typically sits around 80°F at the surface in August, from 8 EPA Water Quality Portal field readings (2024–2025). That is a typical value for the month, not a live reading.
How deep is Clear Lake?
- Clear Lake has a maximum depth of 12 feet. The lake covers 77 acres.
What fish are in Clear Lake?
- Fish species found in Clear Lake include Panfish, Largemouth Bass, Northern Pike. Clear Lake is located in Rock County, Wisconsin.
Are there boat ramps on Clear Lake?
- Clear Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Clear Lake. Public access is listed as yes.
Explore Clear Lake across LakeGrade
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High nutrients, frequent algae, reduced clarity
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Where this data comes from
29 measurements from 1 monitoring station, 2021–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Wisconsin Department of Natural Resources
WIDNR_WQX29 samples · 2021–2025
Analytical methods
- Phosphorus by Colorimetry
Monitoring station identifiers (1)
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.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)
Fish and recreation data from Wisconsin DNR Lakes
Named boat-access points from the USGS National Boat Ramps inventory