Green Lake
Isanti County, Minnesota833 acresView mapDirections
Minnesota PCA publishes the water-quality measurements for Green Lake. Here is what has been measured.
- Eutrophic
- Impaired · Impaired biota (cause unknown)
- Eurasian watermilfoil
- 28 ft max depth
- Public access
Green Lake in Isanti County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 4.7 ft visibility. Phosphorus: 48 µg/L. Chlorophyll-a (algae): 16.4 µg/L. Maximum depth: 28 ft. Surface area: 832.88 acres.
Minnesota DNR's Standard Survey on May 28, 2025 caught 5.89 walleye per gill net at Green Lake. DNR survey details →
Free interactive depth-contour map of Green Lake, reaching a maximum surveyed depth of 25 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Minnesota DNR.
Green Lake is a 833-acre productive, nutrient-rich eutrophic lake in Isanti County, Minnesota with a maximum depth of 28 feet. Overall water quality is improving over recent sampling years. The lake supports 15 documented fish species including black bullhead, black crappie, and bluegill. Public access is available with 1 public boat landing. Compared to the 16 other monitored lakes in Isanti County, Green Lake ranks #12 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-21. Methodology: how these readings are compared.
What Green Lake is good for
From access and monitoring records, not editorial picks.
- Boat launch1 documented ramp
- Fishing15 species recorded
- Ice seasonIce-out around Apr 10
Swimming conditions
Readings onlyRecreation use not supported
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. Green Lake is listed impaired under Clean Water Act §303(d) (IR 5) for impaired biota (cause unknown), mercury, nutrients (phosphorus, nitrogen), pCBs. Check local advisories before you swim.
Whether Green Lake is safe to swim in today is a call for the Minnesota Pollution Control Agency and the Minnesota DNR 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 Minnesota PCA 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.
Murky, only visible to about 4.7 ft. Phosphorus 48 µg/L. Chlorophyll-a 16.4 µg/L. TSI 58.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 4.7ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 48µg/L | Poor GoodFairPoor |
| Chlorophyll-a (algae) | 16.4µg/L | Poor GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 58 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about Green Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Green Lake typically sits around 65°F at the surface in October. Summer average is about 76°F. Usually warmest in Jul (about 79°F) and coldest in May (about 63°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (63°F) to its warmest (79°F).
Typical surface water temperature by month, from 63 field readings (2010–2025) via the EPA Water Quality Portal. See the full Green Lake water temperature breakdown →
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 (387,258 cells/mL) on July 9, 2026.
Blue-green algae can appear and clear within days, so check your state’s current advisory before swimming. EPA CyAN ↗
Minnesota DNR's Standard Survey on May 28, 2025 caught 5.89 walleye per gill net at 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 5 years of monitoring is improving. Catch rate is not a swim clearance and is not a weekly bite report.
DNR Fisheries Survey Summary
13 surveys on file from MN DNR Fisheries. Most recent: 2025-05-28 (Standard Survey).
13 surveys on file · most recent 2025-05-28 (Standard Survey)
| Species | Catch rate (CPUE) | Size | Avg weight |
|---|---|---|---|
| Spottail Shiner | 30.33 | ||
| Yellow Perch | 23.45 | 5–9 in 2025-05-28 | 0.09 lb |
| Largemouth Bass | 22.33 | 3–19 in 2025-05-28 | 1.33 lb |
| Black Crappie | 15.04 | 6–11 in 2025-05-28 | 0.25 lb |
CPUE = catch per unit effort, fish caught per net per set in a standardised survey. It measures abundance, not size, and is not a weekly bite report.
Length Distributions
Number of fish caught at each inch class in the most recent survey that recorded lengths. Red dashed line marks an approximate trophy threshold for that species.
Yellow Perch
Largemouth Bass
Black Crappie
From the 2025-05-28 survey
Green Lake is an 832-acre lake located eight miles east of Princeton and 10 miles west of Cambridge, in west-central Isanti County, and is within the Rum River Watershed. The lake has a maximum depth of 28 feet and an average depth of 21 feet. It is 43% littoral (15 feet or less, 357 acres). Water clarity is generally…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Green Lake. 3 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — GreenFisheries Lake Survey · MN DNR LakeFinder
- —Fish Stocking History — GreenFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — GreenPublic Water Access Sites · MN DNR LakeFinder
Lake Details
Max depth
28 ft
Surface area
833 acres
Shoreline
4.6 mi
Littoral zone
43%
Share shallower than 15 ft
Public access
Yes
Listed by Minnesota PCA
Lake Size & Watershed
Watershed (drainage) area
15 sq mi
HydroLAKES / HydroSHEDS
Elevation
909 ft
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Green LakePublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Stays via Stay22
Stays near Green Lake
Compare lakeside cabins, hotels, and vacation rentals near Green Lake in Isanti County, Minnesota — 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. The water-quality readings cover nutrients and algae, not lodging. Cabins and rentals around Green Lake are listed below.
Top-rated places to stay near Green Lake
Prices for Oct 9–11, 4 adults. Change dates on the map below.
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 whole trip? See where to stay at Minnesota’s top lakes →
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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: Improving
Based on 5 years of monitoring (2021–2025).
Water clarity
Worsening5 years
Phosphorus
Improving-9.65 µg/L/yr4 years
Chlorophyll-a
Improving-2.83 µg/L/yr4 years
Ice season
Typical ice-out
Apr 10
Earliest Mar 22, 2000 · Latest Apr 27, 2014
Typical ice-in
Dec 2
Earliest Nov 20, 2000 · Latest Dec 20, 2001
Most recent ice-out
Apr 27
2014
19 observations · Minnesota PCA ice records
EPA Impairment Status
Green Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
Designated uses not supporting: Aquatic life, Fish consumption, Recreation.
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit MN30-0136-00 · Official waterbody report
Nearby Lakes in Isanti County
Frequently asked questions about Green Lake
Where is Green Lake?
- Green Lake is a lake in Isanti County, Minnesota. Its water-quality measurements are published by Minnesota PCA and shown on this page as reported.
What is the water quality of Green Lake?
- Green Lake in Isanti County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 4.7 ft visibility. Phosphorus: 48 µg/L. Chlorophyll-a (algae): 16.4 µg/L. Maximum depth: 28 ft. Surface area: 832.88 acres.
Is Green Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Green Lake is listed impaired under Clean Water Act §303(d) (IR 5) for impaired biota (cause unknown), mercury, nutrients (phosphorus, nitrogen), pCBs. Check local advisories before you swim.
What is the water temperature of Green Lake?
- Green Lake typically sits around 65°F at the surface in October, from 63 EPA Water Quality Portal field readings (2010–2025). That is a typical value for the month, not a live reading.
How deep is Green Lake?
- Green Lake has a maximum depth of 28 feet. The lake covers 832.88 acres.
What fish are in Green Lake?
- Fish species found in Green Lake include black bullhead, black crappie, bluegill, bowfin (dogfish), brown bullhead, common carp, green sunfish, hybrid sunfish, largemouth bass, northern pike, pumpkinseed, walleye, white sucker, yellow bullhead, yellow perch. Green Lake is located in Isanti County, Minnesota.
What did the DNR fisheries survey find at Green Lake?
- Minnesota DNR's Standard Survey on May 28, 2025 caught 5.89 walleye per gill net at 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 5 years of monitoring is improving. Catch rate is not a swim clearance and is not a weekly bite report.
When does Green Lake thaw?
- Green Lake typically has ice-out around Apr 10. Ice typically forms around Dec 2. The open water season is approximately 236 days.
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 (387,258 cells/mL). Blue-green algae can appear and clear within days, so check Minnesota'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 Green Lake. Public access is listed as yes.
Can I fish at Green Lake?
- Green Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Seasons, size and bag limits, and whether you need a license are set by Minnesota's fish and wildlife agency, so check its current regulations before you go.
Explore Green Lake across LakeQuality
Fish species and the cleanest lakes across Minnesota
Fish species and best lakes in Isanti County
Species activity outlook by water temperature and season
Where to stay at Minnesota's top lakes, each with its readings
Lakes in the Rum River Watershed, ranked by water quality
Minnesota's cleanest lakes, ranked on agency measurements
More lakes in Minnesota
Other Lakes in Minnesota
Eutrophic Lakes in Minnesota
Compare Green Lake With Nearby Lakes
Where this data comes from
128 measurements from 1 monitoring station, 2021–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA128 samples · 2021–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
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
Impairment status from EPA ATTAINS 303(d) database
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder
Named boat-access points from the USGS National Boat Ramps inventory
Ice data from Minnesota DNR Climate