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B

Lost Lake

St. Louis County, MinnesotaMesotrophic

Lost Lake comes in at a B on the grading rubric — a respectable showing for a Minnesota lake of its size and depth. Clarity is the limiting factor — phosphorus is reasonable but suspended particles or algal cells keep water transparency below Minnesota norms.

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. Among the 187 graded lakes in St. Louis County, Lost Lake sits at rank 76, above the county median.

Lost Lake has no invasive species recorded in Minnesota state databases as of 2024, though prevention practices still apply at all access points. The state fisheries records do not list documented species for Lost Lake, which usually reflects a lack of formal fisheries survey work rather than an empty lake. The lake lacks a documented public access point, so visitor use is limited. Multiple sampling years from Minnesota PCA volunteers and partner agencies back the grade, so the letter should hold steady absent a major watershed shift.

Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-10-03. Grade methodology: LakeGrade methodology.

Reviewed by LakeQuality Editorial Team · Updated

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Swimming Safety

Good for swimming, clear water with low algae levels

Water Quality Grade: B, Good

Murky, only visible to about 5.8 ft. Phosphorus level: 17 µg/L. Chlorophyll-a: 6.7 µg/L. Trophic State Index: 49.

MetricValueGrade
Water Clarity (Secchi Depth)5.8 ftD
Phosphorus17 µg/LA
Chlorophyll-a (Algae)6.7 µg/LB
Trophic State Index (TSI)49Mesotrophic

Moderate nutrients, good water quality

Water Quality Trend: Improving

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

MetricTrendChange/YearYears
Water Clarity Improving+0.542 m/yr5
Phosphorus Declining+5 µg/L/yr2
Chlorophyll-a Improving-0.91 µg/L/yr5
See year-by-year chart →

Location

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County Ranking

Ranked #76 of 187 lakes in St. Louis County

Cleaner Lakes Within 30 Miles

Lost Lake holds Grade B. 3 nearby lakes hold higher grades.

See full comparison →

Nearby Lakes in St. Louis County

DNR Reports & Resources

Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Lost Lake. 1 report on file.

EPA Impairment Status

Lost Lake is officially listed as impaired under Clean Water Act §303(d) in the 2019 EPA reporting cycle.

Causes of impairment

Mercury

Source: EPA ATTAINS assessment unit FDL_110 · 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: 2024-10-03

Monitoring stations: 1