Loon Lake
Loon Lake in Cook County, Minnesota has a water quality grade of A (Excellent). 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.
- Clarity
- 17.4 ft
- Typical in August
- 54°F
- Max depth
- 202 ft
- Area
- 1,095 acres
- Type
- Oligotrophic
- Trend
- ↓ Declining
- Public access
- Yes
Next lake in Cook County
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. Water quality is graded A based on 2 sampling years through 2025. 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. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyLow algae
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.
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A (Excellent)
Crystal clear, you can see 17.4 ft down. Phosphorus level: 5 µg/L. Chlorophyll-a: 1.6 µg/L. Trophic State Index: 33.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 17.4 ft | Not graded |
| Phosphorus | 5 µg/L | Good |
| Chlorophyll-a (Algae) | 1.6 µg/L | Good |
| Trophic State Index (TSI) | 33 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay 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.
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Water Temperature
Loon Lake typically sits around 54°F at the surface in August. 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.
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 →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 202 ft |
| Surface Area | 1,095 acres |
| Shoreline Length | 14.3 mi |
| Littoral Zone | 13% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Loon Lake
DNR Fisheries Survey Summary
12 surveys on file from MN DNR Fisheries. Most recent: 2024-08-26 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| CIS | 7.63 | 0.49 lb |
| Tullibee (Cisco) | 7.29 | 0.46 lb |
| Rock Bass | 4.18 | 0.19 lb |
| Lake Trout | 2.03 | 1.33 lb |
| Smallmouth Bass | 1.46 | 0.35 lb |
| Bluegill | 1.31 | 0.19 lb |
CPUE = catch per unit effort, averaged across surveys (excludes juvenile shoreline seining). Higher CPUE = more abundant in standardized sampling.
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.
CIS
Tullibee (Cisco)
Rock Bass
Lake Trout
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
Water Quality Trend: ↓ Declining
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.239 m/yr | 5 |
| Phosphorus | ↓ Declining | +0.1 µg/L/yr | 5 |
| Chlorophyll-a | → Stable | +0.02 µg/L/yr | 5 |
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
Source: EPA ATTAINS assessment unit MN16-0448-00 · Official waterbody report
County Ranking
Ranked #19 of 44 lakes in Cook County
Nearby Lakes in Cook County
Frequently asked questions about Loon Lake
What is the water quality grade for Loon Lake?
- Loon Lake in Cook County, Minnesota has a water quality grade of A (Excellent). 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?
- Excellent for swimming, crystal clear water with minimal algae. Loon Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 1.6 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Loon Lake?
- Loon Lake typically sits around 54°F at the surface in August, 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.
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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)
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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder