Duluth Lake
Duluth Lake in Douglas County, Wisconsin is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 1.6 ft visibility. Phosphorus: 54 µg/L. Chlorophyll-a (algae): 2.9 µg/L.
- Clarity
- 1.6 ft
- Typical in August
- 69°F
- Public access
- Yes
Next lake in Douglas County
Why Duluth 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 Duluth Lake, no EPA ecoregion for this lake, so the National Lakes Assessment condition thresholds cannot be applied. Sampling here has recorded water clarity, phosphorus and algae (chlorophyll-a).
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 WI DNR and volunteer programs, and published through the EPA Water Quality Portal. Read the full grading methodology.
Duluth Lake is a lake in Douglas County, Wisconsin. Limited fish-species data available. Public access is available with 3 public boat landings.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2025-09-22. Grade methodology: LakeGrade methodology.
Watch Duluth Lake water quality
Subscribe for LakeQuality updates by email. No spam, unsubscribe anytime.
Swimming Safety
Not ratedLimited data
Not rated for swimming — there is not enough monitoring data to judge this lake
Water quality measurements for Duluth Lake
These readings exist but do not meet the evidence bar for an A–F grade — see why.
Very murky, less than 1.6 ft of visibility. Phosphorus level: 54 µg/L. Chlorophyll-a: 2.9 µg/L. Trophic State Index: 58.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.6 ft | Not graded |
| Phosphorus | 54 µg/L | Not graded |
| Chlorophyll-a (Algae) | 2.9 µg/L | Not graded |
| Trophic State Index (TSI) | 58 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Duluth Lake
Compare lakeside cabins, hotels, and vacation rentals near Duluth 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 Duluth Lake
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 →
Water Temperature
Duluth Lake typically sits around 69°F at the surface in August. Summer average is about 65°F. Usually warmest in Jul (about 70°F) and coldest in May (about 56°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 72 field readings (2025–2025) via the EPA Water Quality Portal. See the full Duluth Lake water temperature breakdown →
Recreation & Access
- Barkers Island MarinaPublic
- Loons FootPublic
- Park PointPublic
Fishing Duluth Lake
Invasive & Introduced Species
Red chips are ecologically harmful invasive species. Gray chips are stocked or introduced fish that aren't a current ecological concern.
Source: USGS Nonindigenous Aquatic Species (NAS) Database. Hover a chip to see scientific name, ecological context, status, and first-observed year.
EPA Impairment Status
Duluth Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
Source: EPA ATTAINS assessment unit WI10008948 · Official waterbody report · Matched by proximity (2.63 km)
Regulated Pollution Sources Nearby
7 EPA-permitted facilities operate within about 5 miles of Duluth Lake under Clean Water Act (NPDES) discharge permits, including 2 classified by the EPA as major dischargers. 2 facilities have a reported Clean Water Act violation in the past three years.
- Superior Sewage Disposal SystemSuperior · 0.6 mi away · NPDES WI0025593MajorRecent violation
- Calumet Superior LlcSuperior · 2.9 mi away · NPDES WI0003085Major
- Duluth Coastal Infrastructure Dredging ProjectDuluth · 0.8 mi away · NPDES MN0072052Recent violation
- Enbridge Pipelines LlcSuperior · 1.4 mi away · NPDES MN0069175
- Duluth Winnipeg Pacific Rwy SwSuperior · 2.9 mi away · NPDES WI0044831
- Midwest Energy Resources CompanySuperior · 2.9 mi away · NPDES WI0038946
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 Duluth Lake
What is the water quality grade for Duluth Lake?
- Duluth Lake in Douglas County, Wisconsin is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 1.6 ft visibility. Phosphorus: 54 µg/L. Chlorophyll-a (algae): 2.9 µg/L.
Is Duluth Lake safe to swim in?
- Not rated for swimming — there is not enough monitoring data to judge this lake. Duluth Lake is not rated for water quality — its monitoring record does not meet the evidence bar. Algae concentration (chlorophyll-a) is 2.9 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Duluth Lake?
- Duluth Lake typically sits around 69°F at the surface in August, from 72 EPA Water Quality Portal field readings (2025–2025). That is a typical value for the month, not a live reading.
Are there boat ramps on Duluth Lake?
- Duluth Lake has 3 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Barkers Island Marina, Loons Foot, Park Point. Public access is listed as yes.
Explore Duluth Lake across LakeGrade
2 documented falls within 11.5 mi, nearest Upper Falls (Amnicon Falls State Park)
Fish species and top-graded 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 grade
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 and most-polluted lakes, ranked
More Wisconsin Lake Rankings
State Parks Near Duluth Lake
Other Lakes in Wisconsin
Eutrophic Lakes in Wisconsin
Where this data comes from
30 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
MNPCA30 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
Impairment status from EPA ATTAINS 303(d) database
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)
Fish and recreation data from Wisconsin DNR Lakes
Named boat-access points from the USGS National Boat Ramps inventory