Green Lake
Green Lake in Green Lake County, Wisconsin is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 13 ft visibility. Maximum depth: 236 ft. Surface area: 7920 acres.
- Clarity
- 13 ft
- Max depth
- 236 ft
- Area
- 7,920 acres
- Trend
- ↑ Improving
- Public access
- Yes
Next lake in Green Lake County
Why Green Lake has no grade
We grade a lake only when its monitoring record clears the evidence bar: at least three phosphorus or chlorophyll-a samples in the last ten years, scored against EPA National Lakes Assessment thresholds for this lake’s ecoregion. For Green Lake, the only measurement available is water clarity, which is not a water-quality indicator on its own — EPA's National Lakes Assessment does not grade clarity. Sampling here has recorded water clarity, but not phosphorus and algae (chlorophyll-a).
Not Rated is not an F. It is EPA Integrated Reporting Category 3 — insufficient information. The water here may be excellent or poor; nobody has measured enough of it to say. Everything below that has been measured is still reported on this page.
Sampling is run by WI DNR and volunteer programs, and published through the EPA Water Quality Portal. Read the full grading methodology.
Green Lake is a 7,920-acre lake in Green Lake County, Wisconsin with a maximum depth of 236 feet. Overall water quality is improving over recent sampling years. The lake supports 7 documented fish species including Panfish, Largemouth Bass, and Smallmouth Bass. Public access is available with 1 public boat landing and 3 public beaches.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2024-10-21. Grade methodology: LakeGrade methodology.
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Swimming Safety
Not ratedBacteria C
Based on E. coli testing, Green Lake occasionally exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 7.3% of 109 samples across 9 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.
Water quality measurements for Green Lake
These readings exist but do not meet the evidence bar for an A–F grade — see why.
Good clarity, visible to about 13 ft. Trophic State Index: 40.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 13 ft | Not graded |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 40 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Green Lake
Compare lakeside cabins, hotels, and vacation rentals near Green Lake in Green Lake 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 Green Lake
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Planning a trip? Cabins and lodging at Green Lake → · more Wisconsin lake trips
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 low (16,596 cells/mL) on November 8, 2025.
Blue-green algae can appear and clear within days, so check your state’s current advisory before swimming. EPA CyAN ↗
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 236 ft |
| Surface Area | 7,920 acres |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
Fish Species
Click a species to see every graded 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.
WI DNR Lake Profile
Authoritative data from the Wisconsin DNR LakePages. 85 stations on file (most recent sample 2026).
Fish Species (DNR-rated)
Water Quality Trend: ↑ Improving
Based on 3 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.61 m/yr | 3 |
EPA Impairment Status
Green Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit WI10000969 · Official waterbody report
Graded lakes near Green Lake
Green Lake has no grade, but these lakes within a short drive do.
Nearby Lakes in Green Lake County
Frequently asked questions about Green Lake
What is the water quality grade for Green Lake?
- Green Lake in Green Lake County, Wisconsin is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 13 ft visibility. Maximum depth: 236 ft. Surface area: 7920 acres.
Is Green Lake safe to swim in?
- Based on E. coli testing, Green Lake occasionally exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 7.3% of 109 samples across 9 seasons. That works out to a bacteria swim-safety grade of C — a historical summary of past testing, not a current reading. Green Lake is not rated for water quality — its monitoring record does not meet the evidence bar. Bacteria levels can spike quickly after heavy rain, so always check Wisconsin's current beach and health-department advisories before you swim.
How deep is Green Lake?
- Green Lake has a maximum depth of 236 feet. The lake covers 7920 acres.
What fish are in Green Lake?
- Fish species found in Green Lake include Panfish, Largemouth Bass, Smallmouth Bass, Northern Pike, Trout, Walleye, Catfish. Green Lake is located in Green Lake County, Wisconsin.
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 low (16,596 cells/mL). Blue-green algae can appear and clear within days, so check Wisconsin's current advisory before swimming.
Are there boat ramps on Green Lake?
- Green Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Public access is listed as yes.
Explore Green Lake across LakeGrade
Depth, room, public access, and the state wake-sport rules
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Fish species and best lakes in Green Lake County
Species activity outlook by water temperature and season
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Where this data comes from
168 measurements from 1 monitoring station, 2023–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- North American Lake Management Society
NALMS168 samples · 2023–2024
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
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