Loon Lake
Cook County, Minnesota1,095 acresView mapDirections
Minnesota PCA publishes the water-quality measurements for Loon Lake. Here is what has been measured.
- Oligotrophic
- Impaired · Mercury
- 202 ft max depth
- Public access
Loon Lake in Cook County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 17.4 ft visibility. Phosphorus: 5 µg/L. Chlorophyll-a (algae): 1.6 µg/L. Maximum depth: 202 ft. Surface area: 1095.49 acres.
Minnesota DNR's Standard Survey on August 26, 2024 caught 0.17 walleye per trap net at Loon Lake. DNR survey details →
Free interactive depth-contour map of Loon Lake, reaching a maximum surveyed depth of 210 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Minnesota DNR.
Loon Lake is a 1,095-acre cold, clear oligotrophic lake in Cook County, Minnesota with a maximum depth of 202 feet. Overall water quality is declining over recent sampling years. The lake supports 10 documented fish species including bluegill, cisco species, and green sunfish. Public access is available. Compared to the 43 other monitored lakes in Cook County, Loon Lake ranks #19 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-24. Methodology: how these readings are compared.
Loon Lake covers about 1,100 acres in Cook County. If you are planning to stay, you can search lake houses and cabins around Loon Lake on Vrbo, or look for a hotel room near the lake on Booking.com or Expedia.
What Loon Lake is good for
From access and monitoring records, not editorial picks.
- Clear water17.4 ft of visibility
- Fishing10 species recorded
- Deep water202 ft surveyed max depth
- Big water1,095 acres
Swimming conditions
Readings onlyLow algae
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. Loon Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury. Check local advisories before you swim.
Whether Loon 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 Loon Lake
These are the measurements Minnesota PCA publishes for Loon 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 17.4 ft down. Phosphorus 5 µg/L. Chlorophyll-a 1.6 µg/L. TSI 33.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 17.4ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 5µg/L | Good 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. | 33 | Oligotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Low nutrients, clear water. No reading is a swimming clearance.
Ask about Loon Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Loon Lake typically sits around 52°F at the surface in September. Summer average is about 52°F. Usually warmest in Aug (about 54°F) and coldest in May (about 48°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (48°F) to its warmest (54°F).
Typical surface water temperature by month, from 462 field readings (2016–2025) via the EPA Water Quality Portal. See the full Loon Lake water temperature breakdown →
Minnesota DNR's Standard Survey on August 26, 2024 caught 0.17 walleye per trap net at Loon Lake.
A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Loon Lake’s water-quality measurements separately, and the water-quality trend over 5 years of monitoring is declining. Catch rate is not a swim clearance and is not a weekly bite report.
DNR Fisheries Survey Summary
12 surveys on file from MN DNR Fisheries. Most recent: 2024-08-26 (Standard Survey).
12 surveys on file · most recent 2024-08-26 (Standard Survey)
| Species | Catch rate (CPUE) | Size | Avg weight |
|---|---|---|---|
| Tullibee (Cisco) | 7.29 | 9–14 in 2007-08-13 | 0.46 lb |
| Rock Bass | 4.18 | 3–10 in 2024-08-26 | 0.19 lb |
| Lake Trout | 2.03 | 10–32 in 2024-08-26 | 1.33 lb |
| Smallmouth Bass | 1.46 | 5–14 in 2024-08-26 | 0.35 lb |
| Bluegill | 1.31 | 5–7 in 2024-08-26 | 0.19 lb |
CPUE = catch per unit effort, fish caught per net per set in a standardised survey. It measures abundance, not size, and is not a weekly bite report.
Length Distributions
Number of fish caught at each inch class in the most recent survey that recorded lengths. Red dashed line marks an approximate trophy threshold for that species.
Tullibee (Cisco)
Rock Bass
Lake Trout
Smallmouth Bass
From the 2024-08-26 survey
Loon Lake is a large, 1,096-acre lake within Cook County and has a maximum depth of 202 ft. There is a small concrete boat access and two remote campsites located on the northwest side of the lake, just off the Gunflint Trail. Loon Lake is primarily managed for lake trout and smallmouth bass. In 2024, a standard…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Loon Lake. 4 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — LoonFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — Loon (1801)Aquatic Plant Report · MN DNR LakeFinder
- —Aquatic Plant Report — Loon (1834)Aquatic Plant Report · MN DNR LakeFinder
- —Public Water Access Sites — LoonPublic Water Access Sites · MN DNR LakeFinder
Lake Details
Max depth
202 ft
Surface area
1,095 acres
Shoreline
14.3 mi
Littoral zone
13%
Share shallower than 15 ft
Public access
Yes
Listed by Minnesota PCA
Lake Size & Watershed
Watershed (drainage) area
16 sq mi
HydroLAKES / HydroSHEDS
Elevation
1,736 ft
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Stays via Stay22
Stays near Loon Lake
Compare lakeside cabins, hotels, and vacation rentals near Loon 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 Loon 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 Minnesota’s top lakes →
Follow Loon Lake’s readings
Email me when new measurements post for this lake. Updates stay free.
Or email
Fish Species
Click a species to see every lake where it is documented.
Fishing Loon Lake
Water Quality Trend: Worsening
Based on 5 years of monitoring (2021–2025).
Water clarity
Worsening5 years
Phosphorus
Worsening+0.1 µg/L/yr5 years
Chlorophyll-a
Stable+0.02 µg/L/yr5 years
EPA Impairment Status
Loon 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 MN16-0448-00 · Official waterbody report
Nearby Lakes in Cook County
Frequently asked questions about Loon Lake
Where is Loon Lake?
- Loon 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 Loon Lake?
- Loon Lake in Cook County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 17.4 ft visibility. Phosphorus: 5 µg/L. Chlorophyll-a (algae): 1.6 µg/L. Maximum depth: 202 ft. Surface area: 1095.49 acres.
Is Loon Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Loon Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury. Check local advisories before you swim.
What is the water temperature of Loon Lake?
- Loon Lake typically sits around 52°F at the surface in September, from 462 EPA Water Quality Portal field readings (2016–2025). That is a typical value for the month, not a live reading.
How deep is Loon Lake?
- Loon Lake has a maximum depth of 202 feet. The lake covers 1095.49 acres.
What fish are in Loon Lake?
- Fish species found in Loon Lake include bluegill, cisco species, green sunfish, hybrid sunfish, lake trout, northern pike, rock bass, smallmouth bass, walleye, white sucker. Loon Lake is located in Cook County, Minnesota.
What did the DNR fisheries survey find at Loon Lake?
- Minnesota DNR's Standard Survey on August 26, 2024 caught 0.17 walleye per trap net at Loon Lake. A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Loon Lake’s water-quality measurements separately, and the water-quality trend over 5 years of monitoring is declining. Catch rate is not a swim clearance and is not a weekly bite report.
Can I fish at Loon Lake?
- Public access to Loon Lake is listed as yes on the lake record. 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 Loon 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
Other Lakes in Minnesota
Oligotrophic Lakes in Minnesota
Compare Loon Lake With Nearby Lakes
Where this data comes from
64 measurements from 2 monitoring stations, 2021–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA64 samples · 2021–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
Monitoring station identifiers (2)
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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder