South Oscar Lake
Douglas County, MinnesotaMesotrophic
On the LakeGrade rubric, South Oscar Lake pulls an A: clarity at 16.7 ft and 20 µg/L of phosphorus put it in the top bracket for Minnesota. The two scored sub-grades — clarity and phosphorus — track close together, so neither one is dragging the average down.
The lake sits in the mesotrophic zone — the band where most well-managed Minnesota lakes fall. The lake's maximum depth is not yet documented in state morphometric records — context for its physical structure remains limited. The lake's surface area is not consistently recorded across state datasets — physical context remains partial. South Oscar Lake ranks 21 of 51 in Douglas County — solidly in the upper half of the local distribution.
South Oscar Lake is on the Minnesota infested-waters list for zebra mussels — boaters should follow clean-drain-dry protocols when moving gear to or from the lake. The state fisheries records do not list documented species for South Oscar Lake, which usually reflects a lack of formal fisheries survey work rather than an empty 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 2020-09-01. Grade methodology: LakeGrade methodology.
Track South Oscar Lake
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Swimming Safety
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A, Excellent
Crystal clear, you can see 16.7 ft down. Phosphorus level: 20 µg/L. Trophic State Index: 42.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 16.7 ft | A |
| Phosphorus | 20 µg/L | B |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 42 | Mesotrophic |
Moderate nutrients, good water quality
Invasive & Introduced Species
Red chips are ecologically harmful invasive species. Gray chips are stocked or introduced fish that aren't a current ecological concern.
Location
County Ranking
Ranked #21 of 51 lakes in Douglas County
Nearby Lakes in Douglas County
More Minnesota Lake Rankings
State Parks Near South Oscar Lake
Other Grade A Lakes in Minnesota
Mesotrophic Lakes in Minnesota
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for South Oscar Lake. 3 reports on file.
- —Aquatic Plant Report — Oscar (0933)Aquatic Plant Report · MN DNR LakeFinder
- —Fish Stocking History — OscarFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — OscarPublic Water Access Sites · MN DNR LakeFinder
EPA Impairment Status
South Oscar 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 MN21-0257-02 · 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
Most recent sample: 2020-09-01
Monitoring stations: 1