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LakeQuality
B

Little Lake Deep

Cook County, MinnesotaMesotrophic

Little Lake Deep comes in at a B on the grading rubric — a respectable showing for a Minnesota lake of its size and depth. Secchi readings are the weakest of the three parameters, suggesting suspended sediment or algal biomass dominates the optical signal.

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. Within Cook County's 128 graded lakes, Little Lake Deep ranks 65 — below the local median, though not at the bottom.

Zebra mussel presence at Little Lake Deep means the lake's clarity numbers carry an asterisk — filtered water is not the same as nutrient-poor water. The state fisheries records do not list documented species for Little Lake Deep, 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 supported by multiple sampling years from Minnesota PCA volunteers and partner agencies, giving the letter a reasonably stable foundation.

Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-09-09. Grade methodology: LakeGrade methodology.

Swimming Safety

Good for swimming, clear water with low algae levels

Water Quality Grade: B, Good

Very murky, less than -324.8 ft of visibility. Phosphorus level: 14 µg/L. Chlorophyll-a: 3.9 µg/L. Trophic State Index: 43.

MetricValueGrade
Water Clarity (Secchi Depth)-324.8 ftF
Phosphorus14 µg/LA
Chlorophyll-a (Algae)3.9 µg/LA
Trophic State Index (TSI)43Mesotrophic

Moderate nutrients, good water quality

Invasive Species

Eurasian watermilfoilNew Zealand mud snailVHSfaucet snailround gobyruffespiny waterfleawhite perchzebra mussel

Water Quality Trend: Declining

Based on 5 years of monitoring data (2020-2025).

MetricTrendChange/YearYears
Water Clarity Declining-10.747 m/yr4
Phosphorus Declining+2.28 µg/L/yr2
Chlorophyll-a Declining+0.1 µg/L/yr3

Location

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County Ranking

Ranked #65 of 128 lakes in Cook County

Nearby Lakes in Cook County

DNR Reports & Resources

Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Little Lake Deep. 2 reports on file.

Data Sources

Water quality data from the EPA Water Quality Portal

Grading methodology based on Metropolitan Council standards

Most recent sample: 2024-09-09

Monitoring stations: 2