Green Lake
Walworth County, Wisconsin311 acresView mapDirections
Wisconsin DNR publishes the water-quality measurements for Green Lake. Here is what has been measured.
- Mesotrophic
- 2 aquatic invasives
- 57 ft max depth
- Public access
Green Lake in Walworth County, Wisconsin has water-quality measurements published by Wisconsin DNR, shown here as reported. Water clarity: 11 ft visibility. Phosphorus: 10.7 µg/L. Maximum depth: 57 ft. Surface area: 311 acres.
Wisconsin DNR lists Panfish as common on Green Lake. DNR survey details →
Green Lake is a 311-acre mesotrophic lake in Walworth County, Wisconsin with a maximum depth of 57 feet. Overall water quality is declining over recent sampling years. The lake supports 4 documented fish species including Panfish, Largemouth Bass, and Northern Pike. Public access is available. Compared to the 18 other monitored lakes in Walworth County, Green Lake ranks #4 for water quality.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2026-06-12. Methodology: how these readings are compared.
What Green Lake is good for
From access and monitoring records, not editorial picks.
- Clear water11 ft of visibility
- Fishing4 species recorded
- Deep water57 ft surveyed max depth
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 Green 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 Green Lake
These are the measurements Wisconsin DNR publishes for Green Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Good clarity, visible to about 11 ft. Phosphorus 10.7 µg/L. TSI 40.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 11ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 10.7µg/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. | 40 | Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Moderate nutrients, good water quality
Ask about Green Lake
Answers come straight from the public measurements and survey records on this page.
Blue-Green Algae (Cyanobacteria)
There’s no recent EPA CyAN cyanobacteria estimate for Green Lake — clouds, ice, or an off-season gap in coverage. The most recent reading was high (337,287 cells/mL) on April 11, 2026.
Blue-green algae can appear and clear within days, so check your state’s current advisory before swimming. EPA CyAN ↗
Wisconsin DNR lists Panfish as common on Green Lake.
A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Green Lake’s water-quality measurements separately, and the water-quality trend over 7 years of monitoring is declining. Catch rate is not a swim clearance and is not a weekly bite report.
WI DNR Lake Profile
Authoritative data from the Wisconsin DNR LakePages. Monitored by volunteers since 2006. 1 station on file (most recent sample 2025).
Fish Species (DNR-rated)
Lake Details
Max depth
57 ft
Surface area
311 acres
Public access
Yes
Listed by Wisconsin DNR
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Stays near Green Lake
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Fish Species
Click a species to see every lake where it is documented.
Fishing Green 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.
Water Quality Trend: Worsening
Based on 7 years of monitoring (2020–2026).
Water clarity
Worsening7 years
Phosphorus
Stable+0.09 µg/L/yr7 years
Nearby Lakes in Walworth County
Frequently asked questions about Green Lake
Where is Green Lake?
- Green Lake is a lake in Walworth County, Wisconsin. Its water-quality measurements are published by Wisconsin DNR and shown on this page as reported.
What is the water quality of Green Lake?
- Green Lake in Walworth County, Wisconsin has water-quality measurements published by Wisconsin DNR, shown here as reported. Water clarity: 11 ft visibility. Phosphorus: 10.7 µg/L. Maximum depth: 57 ft. Surface area: 311 acres.
Is Green Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
How deep is Green Lake?
- Green Lake has a maximum depth of 57 feet. The lake covers 311 acres.
What fish are in Green Lake?
- Fish species found in Green Lake include Panfish, Largemouth Bass, Northern Pike, Walleye. Green Lake is located in Walworth County, Wisconsin.
What did the DNR fisheries survey find at Green Lake?
- Wisconsin DNR lists Panfish as common on Green Lake. A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Green Lake’s water-quality measurements separately, and the water-quality trend over 7 years of monitoring is declining. Catch rate is not a swim clearance and is not a weekly bite report.
Does Green Lake have blue-green algae?
- There is no recent EPA CyAN cyanobacteria estimate for Green Lake (clouds, ice, or an off-season gap). The most recent reading was high (337,287 cells/mL). Blue-green algae can appear and clear within days, so check Wisconsin's current advisory before swimming.
Can I fish at Green Lake?
- Public access to Green 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 Green Lake across LakeQuality
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Where this data comes from
62 measurements from 1 monitoring station, 2020–2026. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Wisconsin Department of Natural Resources
WIDNR_WQX62 samples · 2020–2026
Analytical methods
- Phosphorus by Colorimetry
Monitoring station identifiers (1)
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
Fish and recreation data from Wisconsin DNR Lakes