Oslo Lake
St. Louis County, MinnesotaLimited DataMesotrophic
Oslo Lake earns a C — middle-of-the-pack water quality, with one or two parameters dragging the average down from a stronger grade.
The lake sits in the mesotrophic zone — the band where most well-managed Minnesota lakes fall. A maximum depth of 36 ft puts Oslo Lake in the middle of Minnesota's depth distribution. The lake is compact at 99 acres, with 3.7 miles of shoreline and little volume to buffer nutrient inputs. Oslo Lake ranks 86 of 187 in St. Louis County — solidly in the upper half of the local distribution.
No invasive species are currently listed at Oslo Lake — the lake remains off the Minnesota infested-waters roster. The lake's fish records list 2 species — a varied community without one dominant gamefish. No formal public access is documented at Oslo Lake — most use is by shoreline residents and their guests. Monitoring depth is thin here: the LakeGrade rubric is applied to a small number of sample years, and the grade will be revised as more data accumulates.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2023-08-08. Grade methodology: LakeGrade methodology.
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Swimming Safety
Generally safe for swimming, moderate water quality
Water Quality Grade: C, Fair
Moderate clarity, visible to about 9.2 ft. Trophic State Index: 45.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 9.2 ft | C |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 45 | Mesotrophic |
Moderate nutrients, good water quality
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 36 ft |
| Surface Area | 99.24 acres |
| Shoreline Length | 3.7 mi |
| Littoral Zone | 58% |
| Public Access | No |
Fish Species
Click a species to see all Minnesota and Wisconsin lakes where it is found.
→ Best fishing times for Oslo Lake (14-day solunar calendar)
→ Is it safe to eat fish from Oslo Lake? (mercury & PFAS guide)
→ Oslo Lake fishing regulations (limits, seasons, special rules)
Water Quality Trend: ↓ Declining
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | -0.006 m/yr | 5 |
| Phosphorus | ↓ Declining | +2.17 µg/L/yr | 4 |
Location
County Ranking
Ranked #86 of 187 lakes in St. Louis County
Cleaner Lakes Within 30 Miles
Oslo Lake holds Grade C. 3 nearby lakes hold higher grades.
Nearby Lakes in St. Louis County
More Minnesota Lake Rankings
Other Grade C Lakes in Minnesota
Mesotrophic Lakes in Minnesota
DNR Fisheries Survey Summary
2 surveys on file from MN DNR Fisheries. Most recent: 2025-07-14 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Northern Pike | 5.67 | 1.61 lb |
| Yellow Perch | 0.25 | 0.09 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.
Northern Pike
Yellow Perch
From the 2025-07-14 survey
Oslo Lake is located approximately eight miles west of Kettle Falls, Minnesota. This 99.2-acre lake has a maximum depth of 36 feet and dark tannin-stained water. A fisheries survey was completed in Oslo Lake during the 2025 field season as part of a regular rotation of surveys in the International Falls Management…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Oslo Lake. 1 report on file.
- —Fisheries Lake Survey — OsloFisheries Lake Survey · MN DNR LakeFinder
EPA Impairment Status
Oslo 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 MN69-0838-00 · 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: 2023-08-08
Monitoring stations: 1