Loon Lake
Blue Earth County, MinnesotaLimited DataEutrophic
Loon Lake grades an F: every scored parameter (clarity) rates poorly, placing it among the most stressed lakes monitored in Minnesota.
Eutrophic conditions are the baseline here: clarity drops noticeably in late summer, and dissolved oxygen near the bottom can become a concern. Loon Lake is a shallow lake at 7 ft maximum depth, which means it warms quickly, mixes constantly, and amplifies nutrient inputs. At 809 acres, Loon Lake fits the Minnesota median for monitored lakes, with 5.3 miles of shoreline. Within the 9 graded lakes of Blue Earth County, Loon Lake sits at rank 9, near the bottom of the county list.
Loon Lake has no invasive species recorded in Minnesota state databases as of 2022, though prevention practices still apply at all access points. Walleye are documented at Loon Lake, one of 13 fish species on record for the lake. Public access is available — the lake is on the Minnesota PCA public-access list. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2022-06-24. Grade methodology: LakeGrade methodology.
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Swimming Safety
Avoid swimming, very poor water quality, potential algae toxins
Water Quality Grade: F, Very Poor
Very murky, less than 2 ft of visibility. Trophic State Index: 67.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2 ft | F |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 67 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 7 ft |
| Surface Area | 808.62 acres |
| Shoreline Length | 5.3 mi |
| Littoral Zone | 100% |
| Public Access | Yes |
Fish Species
Click a species to see all Minnesota and Wisconsin lakes where it is found.
→ Best fishing times for Loon Lake (14-day solunar calendar)
→ Is it safe to eat fish from Loon Lake? (mercury & PFAS guide)
→ Loon Lake fishing regulations (limits, seasons, special rules)
Water Quality Trend: ↓ Declining
Based on 3 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.135 m/yr | 3 |
Location
County Ranking
Ranked #9 of 9 lakes in Blue Earth County
Cleaner Lakes Within 30 Miles
Loon Lake holds Grade F. 4 nearby lakes hold higher grades.
Nearby Lakes in Blue Earth County
More Minnesota Lake Rankings
State Parks Near Loon Lake
Other Grade F Lakes in Minnesota
Eutrophic Lakes in Minnesota
Compare Loon Lake With Nearby Lakes
DNR Fisheries Survey Summary
8 surveys on file from MN DNR Fisheries. Most recent: 2022-08-15 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Black Bullhead | 64.32 | 0.45 lb |
| Common Carp | 29.06 | 2.93 lb |
| Black Crappie | 19.40 | 0.28 lb |
| Walleye | 16.10 | 1.11 lb |
| Yellow Perch | 11.17 | 0.21 lb |
| Bluegill | 7.09 | 0.24 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.
Black Bullhead
Common Carp
Black Crappie
Walleye
From the 2022-08-15 survey
Loon Lake is an 809-acre lake located east of the city of Lake Crystal in northwest Blue Earth County. A DNR-maintained public access is located on the south side of the lake off County Road 9. Loon Lake is shallow with a maximum depth of 7 feet with generally poor water clarity and frequent algal blooms caused by…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Loon Lake. 3 reports on file.
- —Fisheries Lake Survey — LoonFisheries Lake Survey · MN DNR LakeFinder
- —Fish Stocking History — LoonFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — LoonPublic Water Access Sites · MN DNR LakeFinder
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 MN07-0096-00 · Official waterbody report
Data Sources
Water quality data from the EPA Water Quality Portal
Impairment status from EPA ATTAINS 303(d) database
Grading methodology based on Metropolitan Council standards
Lake details from Minnesota DNR LakeFinder
Most recent sample: 2022-06-24
Monitoring stations: 1