Grass Lake
Grass Lake in Anoka County, Minnesota has a water quality grade of A (Excellent). Water clarity: 4.3 ft visibility. Phosphorus: 20 µg/L. Chlorophyll-a (algae): 5.3 µg/L.
- Clarity
- 4.3 ft
- Typical in August
- 77°F
- Type
- Eutrophic
- Trend
- ↑ Improving
- Public access
- Yes
Next lake in Anoka County
Grass Lake is a productive, nutrient-rich eutrophic lake in Anoka County, Minnesota. Water quality is graded A based on 2 sampling years through 2025. Overall water quality is improving over recent sampling years. Limited fish-species data available. Public access is available with 1 public boat landing. 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. Grade methodology: LakeGrade methodology.
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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)
Murky, only visible to about 4.3 ft. Phosphorus level: 20 µg/L. Chlorophyll-a: 5.3 µg/L. Trophic State Index: 50.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 4.3 ft | Not graded |
| Phosphorus | 20 µg/L | Good |
| Chlorophyll-a (Algae) | 5.3 µg/L | Good |
| Trophic State Index (TSI) | 50 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay 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.
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Water Temperature
Grass Lake typically sits around 77°F at the surface in August. 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.
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 →
Recreation & Access
- Mississippi West Regional ParkPublic
Fishing Grass Lake
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
Water Quality Trend: ↑ Improving
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.042 m/yr | 2 |
| Phosphorus | ↑ Improving | -0.75 µg/L/yr | 2 |
| Chlorophyll-a | → Stable | 0 µg/L/yr | 2 |
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.
County Ranking
Ranked #4 of 23 lakes in Anoka County
Nearby Lakes in Anoka County
Frequently asked questions about Grass Lake
What is the water quality grade for Grass Lake?
- Grass Lake in Anoka County, Minnesota has a water quality grade of A (Excellent). Water clarity: 4.3 ft visibility. Phosphorus: 20 µg/L. Chlorophyll-a (algae): 5.3 µg/L.
Is Grass Lake safe to swim in?
- Excellent for swimming, crystal clear water with minimal algae. Grass Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 5.3 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Grass Lake?
- Grass Lake typically sits around 77°F at the surface in August, from 47 EPA Water Quality Portal field readings (2016–2025). That is a typical value for the month, not a live reading.
Are there boat ramps on Grass Lake?
- Grass Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Mississippi West Regional Park. Public access is listed as yes.
Explore Grass Lake across LakeGrade
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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)
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
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Named boat-access points from the USGS National Boat Ramps inventory