St. Louis Bay Lake
St. Louis Bay Lake in Douglas County, Wisconsin has a water quality grade of C (Fair). Water clarity: 1.3 ft visibility. Phosphorus: 68 µg/L. Chlorophyll-a (algae): 1.6 µg/L.
- Clarity
- 1.3 ft
- Typical in August
- 72°F
- Type
- Eutrophic
Next lake in Douglas County
St. Louis Bay Lake is a productive, nutrient-rich eutrophic lake in Douglas County, Wisconsin. Water quality is graded C based on 2 sampling years through 2025. Compared to the 14 other monitored lakes in Douglas County, St. Louis Bay Lake ranks #11 for water quality.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2025-09-22. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyLimited data
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.
Generally safe for swimming, moderate water quality
Water Quality Grade: C (Fair)
Very murky, less than 1.3 ft of visibility. Phosphorus level: 68 µg/L. Chlorophyll-a: 1.6 µg/L. Trophic State Index: 58.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.3 ft | Not graded |
| Phosphorus | 68 µg/L | Poor |
| Chlorophyll-a (Algae) | 1.6 µg/L | Good |
| Trophic State Index (TSI) | 58 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near St. Louis Bay Lake
Compare lakeside cabins, hotels, and vacation rentals near St. Louis Bay Lake in Douglas County, Wisconsin — 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
St. Louis Bay Lake typically sits around 72°F at the surface in August. Summer average is about 72°F. Usually warmest in Jul (about 79°F) and coldest in May (about 64°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 9 field readings (2025–2025) via the EPA Water Quality Portal. See the full St. Louis Bay Lake water temperature breakdown →
Fishing St. Louis Bay Lake
Regulated Pollution Sources Nearby
3 EPA-permitted facilities operate within about 5 miles of St. Louis Bay Lake under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Wisconsin Central Ltd - Proctor Railroad YardProctor · 2.9 mi away · NPDES MN0000361Recent violation
- Kingsbury Bay-Grassy Point Habitat Restoration ProjectDuluth · 0.4 mi away · NPDES MN0071285
- Interstate Island WmaDuluth · 1.5 mi away · NPDES MN0071391
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 #11 of 15 lakes in Douglas County
Nearby Lakes in Douglas County
Frequently asked questions about St. Louis Bay Lake
What is the water quality grade for St. Louis Bay Lake?
- St. Louis Bay Lake in Douglas County, Wisconsin has a water quality grade of C (Fair). Water clarity: 1.3 ft visibility. Phosphorus: 68 µg/L. Chlorophyll-a (algae): 1.6 µg/L.
Is St. Louis Bay Lake safe to swim in?
- Generally safe for swimming, moderate water quality. St. Louis Bay Lake has a water quality grade of C (Fair). Algae concentration (chlorophyll-a) is 1.6 µg/L. Always check local health department advisories before swimming.
What is the water temperature of St. Louis Bay Lake?
- St. Louis Bay Lake typically sits around 72°F at the surface in August, from 9 EPA Water Quality Portal field readings (2025–2025). That is a typical value for the month, not a live reading.
Explore St. Louis Bay Lake across LakeGrade
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High nutrients, frequent algae, reduced clarity
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Where this data comes from
29 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
MNPCA29 samples · 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
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)
Fish and recreation data from Wisconsin DNR Lakes