Loon Lake
Loon Lake in Cass County, Minnesota has a water quality grade of A (Excellent). Water clarity: 12.1 ft visibility. Phosphorus: 14 µg/L. Chlorophyll-a (algae): 3.5 µg/L. Maximum depth: 25 ft. Surface area: 231.75 acres.
- Clarity
- 12.1 ft
- Typical in August
- 75°F
- Max depth
- 25 ft
- Area
- 232 acres
- Type
- Mesotrophic
- Trend
- ↑ Improving
- Public access
- Yes
- Ice-out
- Apr 21
- Open water
- 215 days
Next lake in Cass County
Loon Lake is a 232-acre mesotrophic lake in Cass County, Minnesota with a maximum depth of 25 feet. Water quality is graded A based on 2 sampling years through 2025. Overall water quality is improving over recent sampling years. The lake supports 12 documented fish species including black bullhead, black crappie, and bluegill. Public access is available with 1 public boat landing. Compared to the 103 other monitored lakes in Cass County, Loon Lake ranks #45 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-30. 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)
Good clarity, visible to about 12.1 ft. Phosphorus level: 14 µg/L. Chlorophyll-a: 3.5 µg/L. Trophic State Index: 42.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 12.1 ft | Not graded |
| Phosphorus | 14 µg/L | Good |
| Chlorophyll-a (Algae) | 3.5 µg/L | Good |
| Trophic State Index (TSI) | 42 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Loon Lake
Compare lakeside cabins, hotels, and vacation rentals near Loon Lake in Cass 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 75°F at the surface in August. Summer average is about 75°F. Usually warmest in Jul (about 76°F) and coldest in May (about 58°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 17 field readings (2018–2025) via the EPA Water Quality Portal. See the full Loon Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 25 ft |
| Surface Area | 232 acres |
| Shoreline Length | 2.8 mi |
| Littoral Zone | 93% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Loon LakePublic
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Loon Lake
DNR Fisheries Survey Summary
5 surveys on file from MN DNR Fisheries. Most recent: 2017-07-05 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Brown Bullhead | 36.04 | 0.48 lb |
| Black Bullhead | 17.75 | 0.27 lb |
| Bluegill | 14.04 | 0.23 lb |
| Largemouth Bass | 12.20 | 0.77 lb |
| Yellow Perch | 5.43 | 0.12 lb |
| Northern Pike | 5.28 | 1.59 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.
Brown Bullhead
Black Bullhead
Bluegill
Largemouth Bass
From the 2017-07-05 survey
Loon is a 237 acre lake located two miles southwest of Pequot Lakes in Cass County. Loon is fairly shallow with 91% 15' deep or less. One small hole reaches 25' in depth. During winter months the lake association operates an aerator to try to keep the fish community alive. Winter travelers will need to use extra…
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 (1124)Aquatic Plant Report · MN DNR LakeFinder
- —Fish Stocking History — LoonFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — LoonPublic Water Access Sites · MN DNR LakeFinder
Water Quality Trend: ↑ Improving
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.116 m/yr | 6 |
| Phosphorus | ↓ Declining | +1.11 µg/L/yr | 6 |
| Chlorophyll-a | ↑ Improving | -0.3 µg/L/yr | 6 |
Ice Season
Historical ice data from Minnesota DNR (6 observations).
Estimated open water season: 215 days
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2005-04-10 (2005) | 2008-04-28 (2008) |
| Ice-In | 2004-11-15 (2004) | 2006-11-30 (2006) |
Most recent ice-out: 2008-04-28
EPA Impairment Status
Loon Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit MN11-0226-00 · Official waterbody report
County Ranking
Ranked #45 of 104 lakes in Cass County
Nearby Lakes in Cass County
Frequently asked questions about Loon Lake
What is the water quality grade for Loon Lake?
- Loon Lake in Cass County, Minnesota has a water quality grade of A (Excellent). Water clarity: 12.1 ft visibility. Phosphorus: 14 µg/L. Chlorophyll-a (algae): 3.5 µg/L. Maximum depth: 25 ft. Surface area: 231.75 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 3.5 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Loon Lake?
- Loon Lake typically sits around 75°F at the surface in August, from 17 EPA Water Quality Portal field readings (2018–2025). That is a typical value for the month, not a live reading.
How deep is Loon Lake?
- Loon Lake has a maximum depth of 25 feet. The lake covers 231.75 acres.
What fish are in Loon Lake?
- Fish species found in Loon Lake include black bullhead, black crappie, bluegill, brown bullhead, green sunfish, hybrid sunfish, largemouth bass, northern pike, pumpkinseed, rock bass, walleye, yellow bullhead. Loon Lake is located in Cass County, Minnesota.
When does Loon Lake thaw?
- Loon Lake typically has ice-out around Apr 21. Ice typically forms around Nov 22. The open water season is approximately 215 days.
Are there boat ramps on Loon Lake?
- Loon Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Loon Lake. Public access is listed as yes.
Explore Loon Lake across LakeGrade
Depth, room, public access, and the state wake-sport rules
Fish species and top-graded lakes across Minnesota
Fish species and best lakes in Cass County
Species activity outlook by water temperature and season
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Where to stay at Minnesota's top lakes, each with its grade
Lakes in the Mississippi Headwaters, ranked by water quality
Lakes in the Pine River Watersheds (Brainerd Lakes), ranked by water quality
Moderate nutrients, good water quality
Minnesota's cleanest and most-polluted lakes, ranked
More Minnesota Lake Rankings
State Parks Near Loon Lake
Other Grade A Lakes in Minnesota
Mesotrophic Lakes in Minnesota
Where this data comes from
78 measurements from 1 monitoring station, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA78 samples · 2020–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H 2 ~ Chlorophyll a-b-c Determination by spectrophotometer
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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder
Named boat-access points from the USGS National Boat Ramps inventory
Ice data from Minnesota DNR Climate