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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.

Reviewed by LakeQuality Editorial Team · Updated

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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.

MetricValueGrade
Water Clarity (Secchi Depth)16.7 ftA
Phosphorus20 µg/LB
Chlorophyll-a (Algae)No data
Trophic State Index (TSI)42Mesotrophic

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.

Eurasian watermilfoilzebra mussel

Location

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County Ranking

Ranked #21 of 51 lakes in Douglas County

Nearby Lakes in Douglas County

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.

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

Mercury

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