St. Louis Bay Lake
Douglas County, WisconsinView mapDirections
Wisconsin DNR publishes the water-quality measurements for St. Louis Bay Lake. Here is what has been measured.
- Eutrophic
- Limited data
St. Louis Bay Lake in Douglas County, Wisconsin has water-quality measurements published by Wisconsin DNR, shown here as reported. Water clarity: 1.3 ft visibility. Phosphorus: 68 µg/L. Chlorophyll-a (algae): 1.6 µg/L.
St. Louis Bay Lake is a productive, nutrient-rich eutrophic lake in Douglas County, Wisconsin. 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. Methodology: how these readings are compared.
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. Check local advisories before you swim.
Whether St. Louis Bay Lake is safe to swim in today is a call for the Wisconsin Department of Natural Resources and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for St. Louis Bay Lake
These are the measurements Wisconsin DNR publishes for St. Louis Bay Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Very murky, less than 1.3 ft of visibility. Phosphorus 68 µg/L. Chlorophyll-a 1.6 µg/L. TSI 58.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 1.3ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 68µg/L | Poor GoodFairPoor |
| Chlorophyll-a (algae) | 1.6µg/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. | 58 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about St. Louis Bay Lake
Answers come straight from the public measurements and survey records on this page.
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.
Column height runs from this lake’s coldest month (64°F) to its warmest (79°F).
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 →
Stays via Stay22
Stays 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.
Top-rated places to stay near St. Louis Bay Lake
Prices for Oct 9–11, 4 adults. Change dates on the map below.
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Planning a whole trip? See where to stay at Wisconsin’s top lakes →
Follow St. Louis Bay Lake’s readings
Email me when new measurements post for this lake. Updates stay free.
Or email
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.
Nearby Lakes in Douglas County
Frequently asked questions about St. Louis Bay Lake
Where is St. Louis Bay Lake?
- St. Louis Bay Lake is a lake in Douglas County, Wisconsin. Its water-quality measurements are published by Wisconsin DNR and shown on this page as reported.
What is the water quality of St. Louis Bay Lake?
- St. Louis Bay Lake in Douglas County, Wisconsin has water-quality measurements published by Wisconsin DNR, shown here as reported. 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?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
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 LakeQuality
Fish species and the cleanest lakes across Wisconsin
Fish species and best lakes in Douglas County
Species activity outlook by water temperature and season
Where to stay at Wisconsin's top lakes, each with its readings
Lakes in the St. Croix Watershed, ranked by water quality
Lakes in the Lake Superior Basin (MN+WI), ranked by water quality
Wisconsin's cleanest lakes, ranked on agency measurements
More lakes in Wisconsin
State Parks Near St. Louis Bay Lake
Other Lakes in Wisconsin
Eutrophic Lakes in Wisconsin
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)
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)
Fish and recreation data from Wisconsin DNR Lakes