Slate Lake
Lake County, Minnesota293 acresView mapDirections
Minnesota PCA publishes the water-quality measurements for Slate Lake. Here is what has been measured.
- Mesotrophic
- Impaired · Mercury
- 7 ft max depth
- Public access
- Limited data
Slate Lake in Lake County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 4.4 ft visibility. Phosphorus: 22 µg/L. Chlorophyll-a (algae): 4.6 µg/L. Maximum depth: 7 ft. Surface area: 293.02 acres.
Slate Lake is a 293-acre mesotrophic lake in Lake County, Minnesota with a maximum depth of 7 feet. Overall water quality is declining over recent sampling years. The lake supports 8 documented fish species including bluegill, northern pike, and pumpkinseed. Public access is available. Compared to the 34 other monitored lakes in Lake County, Slate Lake ranks #19 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-16. Methodology: how these readings are compared.
What Slate Lake is good for
From access and monitoring records, not editorial picks.
- Fishing8 species recorded
- Ice seasonIce-out around May 1
Swimming conditions
Readings onlyLimited data
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. Slate Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury. Check local advisories before you swim.
Whether Slate 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 Slate Lake
These are the measurements Minnesota PCA publishes for Slate 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 4.4 ft. Phosphorus 22 µg/L. Chlorophyll-a 4.6 µg/L. TSI 50.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 4.4ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 22µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 4.6µg/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 | Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Moderate nutrients, good water quality
Ask about Slate Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Slate Lake typically sits around 67°F at the surface in September. Summer average is about 71°F. Usually warmest in Jun (about 73°F) and coldest in May (about 50°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (50°F) to its warmest (73°F).
Typical surface water temperature by month, from 15 field readings (2025–2025) via the EPA Water Quality Portal. See the full Slate Lake water temperature breakdown →
Lake Details
Max depth
7 ft
Surface area
293 acres
Shoreline
8.1 mi
Littoral zone
100%
Share shallower than 15 ft
Public access
Yes
Listed by Minnesota PCA
Lake Size & Watershed
Watershed (drainage) area
187 sq mi
HydroLAKES / HydroSHEDS
Elevation
1,631 ft
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
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Stays near Slate Lake
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Follow Slate Lake’s readings
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Fish Species
Click a species to see every lake where it is documented.
Fishing Slate Lake
Water quality readings over time
3 seasons of samples on record (2021–2025). Calling a direction takes at least 4 years of the same measurement.
Water clarity
Worsening3 years
Ice season
Typical ice-out
May 1
Earliest Apr 24, 2026 · Latest May 5, 2023
Most recent ice-out
Apr 24
2026
6 observations · Minnesota PCA ice records
EPA Impairment Status
Slate 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: Fish consumption.
Source: EPA ATTAINS assessment unit MN38-0666-00 · Official waterbody report
Nearby Lakes in Lake County
Frequently asked questions about Slate Lake
Where is Slate Lake?
- Slate Lake is a lake in Lake County, Minnesota. Its water-quality measurements are published by Minnesota PCA and shown on this page as reported.
What is the water quality of Slate Lake?
- Slate Lake in Lake County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 4.4 ft visibility. Phosphorus: 22 µg/L. Chlorophyll-a (algae): 4.6 µg/L. Maximum depth: 7 ft. Surface area: 293.02 acres.
Is Slate Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Slate Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury. Check local advisories before you swim.
What is the water temperature of Slate Lake?
- Slate Lake typically sits around 67°F at the surface in September, from 15 EPA Water Quality Portal field readings (2025–2025). That is a typical value for the month, not a live reading.
How deep is Slate Lake?
- Slate Lake has a maximum depth of 7 feet. The lake covers 293.02 acres.
What fish are in Slate Lake?
- Fish species found in Slate Lake include bluegill, northern pike, pumpkinseed, rock bass, smallmouth bass, walleye, white sucker, yellow perch. Slate Lake is located in Lake County, Minnesota.
When does Slate Lake thaw?
- Slate Lake typically has ice-out around May 1.
Can I fish at Slate Lake?
- Public access to Slate 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 Slate Lake across LakeQuality
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Where this data comes from
15 measurements from 1 monitoring station, 2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA15 samples · 2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent 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
Ice data from Minnesota DNR Climate