Grass Lake
Anoka County, MinnesotaView mapDirections
Minnesota PCA publishes the water-quality measurements for Grass Lake. Here is what has been measured.
- Eutrophic
- Public access
Grass Lake in Anoka County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 4.3 ft visibility. Phosphorus: 20 µg/L. Chlorophyll-a (algae): 5.3 µg/L.
Grass Lake is a productive, nutrient-rich eutrophic lake in Anoka County, Minnesota. Overall water quality is improving over recent sampling years. Limited fish-species data available. Public access is available. Compared to the 22 other monitored lakes in Anoka County, Grass Lake ranks #4 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-24. Methodology: how these readings are compared.
Swimming conditions
Readings onlyLow algae
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. Check local advisories before you swim.
Whether Grass 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 Grass Lake
These are the measurements Minnesota PCA publishes for Grass 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 4.3 ft. Phosphorus 20 µg/L. Chlorophyll-a 5.3 µg/L. TSI 50.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 4.3ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 20µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 5.3µg/L | Good GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 50 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about Grass Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Grass Lake typically sits around 67°F at the surface in September. Summer average is about 77°F. Usually warmest in Jul (about 79°F) and coldest in May (about 65°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (65°F) to its warmest (79°F).
Typical surface water temperature by month, from 47 field readings (2016–2025) via the EPA Water Quality Portal. See the full Grass Lake water temperature breakdown →
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Grass Lake. 1 report on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fish Stocking History — GrassFish Stocking History · MN DNR LakeFinder
Stays via Stay22
Stays near Grass Lake
Compare lakeside cabins, hotels, and vacation rentals near Grass Lake in Anoka 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.
Top-rated places to stay near Grass Lake
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Planning a whole trip? See where to stay at Minnesota’s top lakes →
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Fishing Grass Lake
Water quality readings over time
2 seasons of samples on record (2021–2025). Calling a direction takes at least 4 years of the same measurement.
Water clarity
Improving2 years
Phosphorus
Improving-0.75 µg/L/yr2 years
Chlorophyll-a
Stable0 µg/L/yr2 years
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Grass Lake under Clean Water Act (NPDES) discharge permits.
- Vision-Ease Lens IncRamsey · 0.9 mi away · NPDES MN0065501
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.
Nearby Lakes in Anoka County
Frequently asked questions about Grass Lake
Where is Grass Lake?
- Grass Lake is a lake in Anoka County, Minnesota. Its water-quality measurements are published by Minnesota PCA and shown on this page as reported.
What is the water quality of Grass Lake?
- Grass Lake in Anoka County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 4.3 ft visibility. Phosphorus: 20 µg/L. Chlorophyll-a (algae): 5.3 µg/L.
Is Grass Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
What is the water temperature of Grass Lake?
- Grass Lake typically sits around 67°F at the surface in September, from 47 EPA Water Quality Portal field readings (2016–2025). That is a typical value for the month, not a live reading.
Can I fish at Grass Lake?
- Public access to Grass Lake is listed as yes on the lake record. 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 Grass Lake across LakeQuality
Fish species and the cleanest lakes across Minnesota
Fish species and best lakes in Anoka 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
Where this data comes from
89 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
MNPCA89 samples · 2021–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- Turbidity by Nephelometry
- Turbidity, Nephelometric Method
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
Regulated discharger data from EPA ECHO (ICIS-NPDES)