Green Lake
Green Lake in Isanti County, Minnesota has a water quality grade of D (Nutrient-rich). 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.
- Clarity
- 4.7 ft
- Typical in August
- 76°F
- Max depth
- 28 ft
- Area
- 833 acres
- Type
- Eutrophic
- Trend
- ↑ Improving
- Public access
- Yes
- Ice-out
- Apr 10
- Open water
- 236 days
Grade D measures nutrients and algae, not whether this is a good place for a cabin trip. Cabins and rentals near Green Lake →
Next lake in Isanti County
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. Water quality is graded D based on 2 sampling years through 2025. 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 2 public boat landings. 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. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyAlgae risk
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.
Nutrients and algae run higher than average — check local advisories before swimming, and skip the water if you see scum
Water Quality Grade: D (Nutrient-rich)
Murky, only visible to about 4.7 ft. Phosphorus level: 48 µg/L. Chlorophyll-a: 16.4 µg/L. Trophic State Index: 58.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 4.7 ft | Not graded |
| Phosphorus | 48 µg/L | Poor |
| Chlorophyll-a (Algae) | 16.4 µg/L | Poor |
| Trophic State Index (TSI) | 58 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay 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 grade measures nutrients and algae, not lodging — cabins and rentals around Green Lake are listed below.
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 whole trip? See where to stay at Minnesota’s top lakes →
Water Temperature
Green Lake typically sits around 76°F at the surface in August. 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.
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 ↗
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 28 ft |
| Surface Area | 833 acres |
| Shoreline Length | 4.6 mi |
| Littoral Zone | 43% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Green LakePublic
- Highway 7 BridgePublic
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.
DNR Fisheries Survey Summary
13 surveys on file from MN DNR Fisheries. Most recent: 2025-05-28 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| SUN | 115.79 | — |
| Spottail Shiner | 30.33 | — |
| Yellow Perch | 23.45 | 0.09 lb |
| Largemouth Bass | 22.33 | 1.33 lb |
| Black Crappie | 15.04 | 0.25 lb |
| IOD | 14.00 | — |
CPUE = catch per unit effort, averaged across surveys (excludes juvenile shoreline seining). Higher CPUE = more abundant in standardized sampling.
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
Water Quality Trend: ↑ Improving
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.034 m/yr | 5 |
| Phosphorus | ↑ Improving | -9.65 µg/L/yr | 4 |
| Chlorophyll-a | ↑ Improving | -2.83 µg/L/yr | 4 |
Ice Season
Historical ice data from Minnesota DNR (19 observations).
Estimated open water season: 236 days
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2000-03-22 (2000) | 2014-04-27 (2014) |
| Ice-In | 2000-11-20 (2000) | 2001-12-20 (2001) |
Most recent ice-out: 2014-04-27
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
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit MN30-0136-00 · Official waterbody report
County Ranking
Ranked #12 of 17 lakes in Isanti County
Nearby Lakes With Higher Grades
Green Lake holds Grade D. One nearby lake has a higher nutrient-and-algae grade — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in Isanti County
Frequently asked questions about Green Lake
What is the water quality grade for Green Lake?
- Green Lake in Isanti County, Minnesota has a water quality grade of D (Nutrient-rich). 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?
- Nutrients and algae run higher than average — check local advisories before swimming, and skip the water if you see scum. Green Lake has a water quality grade of D (Nutrient-rich). Algae concentration (chlorophyll-a) is 16.4 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Green Lake?
- Green Lake typically sits around 76°F at the surface in August, 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.
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 2 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Green Lake, Highway 7 Bridge. Public access is listed as yes.
Explore Green Lake across LakeGrade
Fish species and top-graded 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 grade
Lakes in the Rum River Watershed, ranked by water quality
High nutrients, frequent algae, reduced clarity
Minnesota's cleanest and most-polluted lakes, ranked
More Minnesota Lake Rankings
Other Grade D Lakes in Minnesota
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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)
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)
Lake details from Minnesota DNR LakeFinder
Named boat-access points from the USGS National Boat Ramps inventory
Ice data from Minnesota DNR Climate