Superior Lake
Cook County, MinnesotaView mapDirections
Minnesota PCA publishes the water-quality measurements for Superior Lake. Here is what has been measured.
- Impaired · Mercury
- 6 aquatic invasives
- Public access
- Limited data
Superior Lake in Cook County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 15.1 ft visibility. Phosphorus: 4 µg/L. Chlorophyll-a (algae): 1.2 µg/L.
Superior Lake is a lake in Cook County, Minnesota. Phosphorus level is declining over recent sampling years. Limited fish-species data available. Public access is available with 2 public boat landings.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-09-17. Methodology: how these readings are compared.
What Superior Lake is good for
From access and monitoring records, not editorial picks.
- Clear water15.1 ft of visibility
- Boat launch2 documented ramps
Swimming conditions
No readingBacteria tested: low
Based on E. coli testing, Superior Lake rarely exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 2.3% of 129 samples across 5 seasons.
This is a historical summary of past testing, not a current condition — bacteria levels change quickly, especially after rain. Always check Minnesota’s current beach and health-department advisories before swimming.
Whether Superior 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 Superior Lake
These are the measurements Minnesota PCA publishes for Superior Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Crystal clear, you can see 15.1 ft down. Phosphorus 4 µg/L. Chlorophyll-a 1.2 µg/L. TSI 32.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 15.1ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 4µg/L | Measured, not scored The nutrient that most limits algae growth in freshwater. More phosphorus, more algae potential. |
| Chlorophyll-a (algae) | 1.2µg/L | Measured, not scored The green pigment in algae — a direct measure of how much algae is in the water. |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 32 | Oligotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Low nutrients, clear water. No reading is a swimming clearance.
Ask about Superior Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Superior Lake typically sits around 49°F at the surface in October. Summer average is about 49°F. Usually warmest in Sep (about 57°F) and coldest in May (about 40°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (40°F) to its warmest (57°F).
Typical surface water temperature by month, from 1,298 field readings (2016–2024) via the EPA Water Quality Portal. See the full Superior Lake water temperature breakdown →
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Superior Lake. 2 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fish Stocking History — SuperiorFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — SuperiorPublic Water Access Sites · MN DNR LakeFinder
Recreation & Access
- Grand Marais Safe HarborPublic
- Grand Marais WestPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Stays via Stay22
Stays near Superior Lake
Compare lakeside cabins, hotels, and vacation rentals near Superior Lake in Cook 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 Superior 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 trip? Cabins and lodging at Superior Lake → · more Minnesota lake trips
Follow Superior Lake’s readings
Email me when new measurements post for this lake. Updates stay free.
Or email
Fishing Superior 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.
Water quality readings over time
2 seasons of samples on record (2023–2024). Calling a direction takes at least 4 years of the same measurement.
Water clarity
Stable2 years
Phosphorus
Worsening+0.5 µg/L/yr2 years
Chlorophyll-a
Improving-0.5 µg/L/yr2 years
EPA Impairment Status
Superior 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 MN16-0001-00 · Official waterbody report
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Superior Lake under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Grand Marais WwtpGrand Marais · 0.6 mi away · NPDES MN0020010Recent violation
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 Cook County
Frequently asked questions about Superior Lake
Where is Superior Lake?
- Superior Lake is a lake in Cook County, Minnesota. Its water-quality measurements are published by Minnesota PCA and shown on this page as reported.
What is the water quality of Superior Lake?
- Superior Lake in Cook County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 15.1 ft visibility. Phosphorus: 4 µg/L. Chlorophyll-a (algae): 1.2 µg/L.
Is Superior Lake safe to swim in?
- Based on E. coli testing, Superior Lake rarely exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 2.3% of 129 samples across 5 seasons. That is a historical summary of past bacteria testing, not a current reading and not a swimming clearance. Bacteria levels can spike quickly after heavy rain, so whether Superior Lake is safe to swim in today is a call for Minnesota's water agency and the county health department; check their current beach advisories before you swim.
What is the water temperature of Superior Lake?
- Superior Lake typically sits around 49°F at the surface in October, from 1,298 EPA Water Quality Portal field readings (2016–2024). That is a typical value for the month, not a live reading.
Are there boat ramps on Superior Lake?
- Superior Lake has 2 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Grand Marais Safe Harbor, Grand Marais West. Public access is listed as yes.
Can I fish at Superior Lake?
- Superior Lake has 2 documented boat landings in the USGS National Boat Ramps inventory. 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 Superior Lake across LakeQuality
Fish species and the cleanest lakes across Minnesota
Fish species and best lakes in Cook County
Species activity outlook by water temperature and season
Where to stay at Minnesota's top lakes, each with its readings
Lakes in the Lake Superior Basin (MN+WI), ranked by water quality
Minnesota's cleanest lakes, ranked on agency measurements
More lakes in Minnesota
State Parks Near Superior Lake
Other Lakes in Minnesota
Oligotrophic Lakes in Minnesota
Where this data comes from
124 measurements from 6 monitoring stations, 2023–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA124 samples · 2023–2024
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
Monitoring station identifiers (6)
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
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Named boat-access points from the USGS National Boat Ramps inventory