Green Lake
Green Lake in Green Lake County, Wisconsin has a water quality grade of A (Excellent). Water clarity: 13.5 ft visibility. Phosphorus: 38.1 µg/L. Chlorophyll-a (algae): 4.4 µg/L. Maximum depth: 236 ft. Surface area: 7920 acres.
- Clarity
- 13.5 ft
- Max depth
- 236 ft
- Area
- 7,920 acres
- Type
- Mesotrophic
- Trend
- ↑ Improving
- 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 A based on 2 sampling years through 2026. 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 3 public beaches. Compared to the 6 other monitored lakes in Green Lake County, Green Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2026-06-10. Grade methodology: LakeGrade methodology.
Watch Green Lake water quality
Subscribe for LakeQuality updates by email. No spam, unsubscribe anytime.
Green Lake Water Quality Report Card (2026)
A printable one-page report card for Green Lake: grade, clarity, phosphorus, algae, multi-year trend, depth, and fish — with sources.
Swimming Safety
Grade onlyLow algae
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.
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A (Excellent)
Good clarity, visible to about 13.5 ft. Phosphorus level: 38.1 µg/L. Chlorophyll-a: 4.4 µg/L. Trophic State Index: 47.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 13.5 ft | Not graded |
| Phosphorus | 38.1 µg/L | Good |
| Chlorophyll-a (Algae) | 4.4 µg/L | Good |
| Trophic State Index (TSI) | 47 | 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
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Planning a trip? Cabins and lodging at Green Lake → · more Wisconsin lake trips
Current Conditions
USGS snapshot Jul 6, 2026, 5:00 AM from gauge 434840089000001 (Green Lake at Green Lake, WI). Station page ↗ — a live reading replaces this snapshot when the gauge responds. Missing live data is not an all-clear.
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 (376,704 cells/mL) on September 16, 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)
DNR Reports & Resources
Wisconsin DNR Fisheries scientists publish multi-year survey reports for Green Lake covering fish populations, stocking, water quality, and management. 3 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- 2024Little Green Lake comprehensive survey, 2024Comprehensive Survey · WI DNR · 2024 (PDF)
- 2023Big Green Lake creel survey, 2023Creel Survey · WI DNR · 2023 (PDF)
- 2022Big Green Lake comprehensive survey, 2022Comprehensive Survey · WI DNR · 2022 (PDF)
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
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Green Lake under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Green Lake Sanitary DistrictGreen Lake · 2.2 mi away · NPDES WI0036846Recent 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 7 lakes in Green Lake County
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 A (Excellent). Water clarity: 13.5 ft visibility. Phosphorus: 38.1 µg/L. Chlorophyll-a (algae): 4.4 µg/L. Maximum depth: 236 ft. Surface area: 7920 acres.
Is Green Lake safe to swim in?
- Excellent for swimming, crystal clear water with minimal algae. Green Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 4.4 µg/L. 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.
What is the water level at Green Lake?
- The USGS snapshot on this page for Green Lake is 6.68 ft of gage height, recorded Jul 6, 2026, 5:00 AM at gauge 434840089000001. Current Conditions hydrates a live NWIS reading from that same station when the gauge responds. A missed live fetch is not an all-clear.
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 (376,704 cells/mL). Blue-green algae can appear and clear within days, so check Wisconsin's current advisory before swimming.
Explore Green Lake across LakeGrade
Fish species and top-graded lakes across Wisconsin
Fish species and best lakes in Green Lake County
Species activity outlook by water temperature and season
Where to stay at Wisconsin's top lakes, each with its grade
Moderate nutrients, good water quality
Wisconsin's cleanest and most-polluted lakes, ranked
More Wisconsin Lake Rankings
Other Grade A Lakes in Wisconsin
Mesotrophic Lakes in Wisconsin
Compare Green Lake With Nearby Lakes
Where this data comes from
520 measurements from 8 monitoring stations, 2020–2026. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- USGS Wisconsin Water Science Center
USGS-WI298 samples · 2020–2023 - Wisconsin Department of Natural Resources
WIDNR_WQX222 samples · 2023–2026
Analytical methods
- Phosphorus by Colorimetry
- Turbidity in Water
Monitoring station identifiers (8)
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