Loon Lake
Loon Lake in St. Louis County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 6.6 ft visibility. Chlorophyll-a (algae): 2.8 µg/L.
- Clarity
- 6.6 ft
Next lake in St. Louis County
Why Loon Lake has no grade
We grade a lake only when its monitoring record clears the evidence bar: at least three phosphorus or chlorophyll-a samples in the last ten years, scored against EPA National Lakes Assessment thresholds for this lake’s ecoregion. For Loon Lake, no nutrient or algae measurement meets the evidence bar (at least 3 samples within 10 years). Sampling here has recorded water clarity and algae (chlorophyll-a), but not phosphorus.
Not Rated is not an F. It is EPA Integrated Reporting Category 3 — insufficient information. The water here may be excellent or poor; nobody has measured enough of it to say. Everything below that has been measured is still reported on this page.
Sampling is run by MPCA and volunteer programs, and published through the EPA Water Quality Portal. Read the full grading methodology.
Loon Lake is a lake in St. Louis County, Minnesota.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-07-22. Grade methodology: LakeGrade methodology.
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Swimming Safety
Not ratedLimited data
Not rated for swimming — there is not enough monitoring data to judge this lake
Water quality measurements for Loon Lake
These readings exist but do not meet the evidence bar for an A–F grade — see why.
Murky, only visible to about 6.6 ft. Chlorophyll-a: 2.8 µg/L. Trophic State Index: 45.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 6.6 ft | Not graded |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | 2.8 µg/L | Not graded |
| Trophic State Index (TSI) | 45 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Loon Lake
Compare lakeside cabins, hotels, and vacation rentals near Loon Lake in St. Louis 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 Loon Lake
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Fishing Loon Lake
EPA Impairment Status
Loon Lake is officially listed as impaired under Clean Water Act §303(d) in the 2019 EPA reporting cycle.
Causes of impairment
Source: EPA ATTAINS assessment unit FDL_111 · Official waterbody report · Matched by proximity (2.06 km)
Graded lakes near Loon Lake
Loon Lake has no grade, but these lakes within a short drive do.
Nearby Lakes in St. Louis County
Frequently asked questions about Loon Lake
What is the water quality grade for Loon Lake?
- Loon Lake in St. Louis County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 6.6 ft visibility. Chlorophyll-a (algae): 2.8 µg/L.
Is Loon Lake safe to swim in?
- Not rated for swimming — there is not enough monitoring data to judge this lake. Loon Lake is not rated for water quality — its monitoring record does not meet the evidence bar. Algae concentration (chlorophyll-a) is 2.8 µg/L. Always check local health department advisories before swimming.
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Where this data comes from
16 measurements from 1 monitoring station, 2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Fond du Lac Band of Chippewa (MN)
FONDULAC_WQX16 samples · 2024
Analytical methods
- 10200 H ~ Chlorophyll a-b-c Determination
- For determination of Copper by the Bicinchoninate 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
Impairment status from EPA ATTAINS 303(d) database