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.
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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.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 5.8 ft | D |
| Phosphorus | 17 µg/L | A |
| Chlorophyll-a (Algae) | 6.7 µg/L | B |
| Trophic State Index (TSI) | 49 | Mesotrophic |
Moderate nutrients, good water quality
Water Quality Trend: ↑ Improving
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.542 m/yr | 5 |
| Phosphorus | ↓ Declining | +5 µg/L/yr | 2 |
| Chlorophyll-a | ↑ Improving | -0.91 µg/L/yr | 5 |
Location
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.
- AJoe Martin LakeSt. Louis County · mi · Higher grade (B → A)
- BLac LakeCarlton County · mi · Higher overall water quality score
- BLoon LakeSt. Louis County · mi · Higher overall water quality score
Nearby Lakes in St. Louis County
More Minnesota Lake Rankings
State Parks Near Lost Lake
Other Grade B 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 Lost Lake. 1 report on file.
- —Aquatic Plant Report — Lost (0467)Aquatic Plant Report · MN DNR LakeFinder
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
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