Green Lake
Green Lake in Green Lake County, Wisconsin has a water quality grade of B (Good). Phosphorus: 20.6 µg/L. Maximum depth: 236 ft. Surface area: 7920 acres.
- Max depth
- 236 ft
- Area
- 7,920 acres
- Type
- Mesotrophic
- Public access
- Yes
Next lake in Green Lake County
Green Lake is a 7,920-acre mesotrophic lake in Green Lake County, Wisconsin with a maximum depth of 236 feet. Water quality is graded B based on 1 sampling years through 2025. The lake supports 7 documented fish species including Panfish, Largemouth Bass, and Smallmouth Bass. Public access is available with 3 public beaches. Compared to the 6 other monitored lakes in Green Lake County, Green Lake ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2025-02-25. Grade methodology: LakeGrade methodology.
Watch Green Lake water quality
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Swimming Safety
Grade onlyLimited data
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.
Good for swimming, clear water with low algae levels
Water Quality Grade: B (Good)
No clarity data. Phosphorus level: 20.6 µg/L. Trophic State Index: 48.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 20.6 µg/L | Good |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 48 | 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 (14,060 cells/mL) on January 17, 2026.
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
- Deacon Mills ParkPublic
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)
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
County Ranking
Ranked #2 of 7 lakes in Green Lake County
Nearby Lakes With Higher Grades
Green Lake holds Grade B. One nearby lake has a higher nutrient-and-algae grade — useful for a swim day, not a reason to skip lodging here.
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 has a water quality grade of B (Good). Phosphorus: 20.6 µg/L. Maximum depth: 236 ft. Surface area: 7920 acres.
Is Green Lake safe to swim in?
- Good for swimming, clear water with low algae levels. Green Lake has a water quality grade of B (Good). Always check local health department advisories before swimming.
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 (14,060 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. Named access points include Deacon Mills Park. Public access is listed as yes.
Explore Green Lake across LakeGrade
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Moderate nutrients, good water quality
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Where this data comes from
50 measurements from 1 monitoring station, 2024–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Wisconsin Department of Natural Resources
WIDNR_WQX50 samples · 2024–2025
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
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