Thomas Lake
Hennepin County, MinnesotaEutrophic
Thomas Lake earns a D — measurements through 2022 show persistent nutrient pressure that limits clarity through the summer. clarity and phosphorus rate similarly, so there is no obvious single lever to pull on watershed management.
A TSI in the eutrophic range signals a lake doing what nutrient-loaded waters do — supporting an active algal community at the cost of clear water. 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 95 graded lakes in Hennepin County, Thomas Lake sits at rank 42, above the county median.
Thomas Lake has no invasive species recorded in Minnesota state databases as of 2022, though prevention practices still apply at all access points. The state fisheries records do not list documented species for Thomas Lake, which usually reflects a lack of formal fisheries survey work rather than an empty lake. No formal public access is documented at Thomas Lake — most use is by shoreline residents and their guests. Monitoring depth is thin here: the LakeGrade rubric is applied to a small number of sample years, and the grade will be revised as more data accumulates.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2022-09-20. Grade methodology: LakeGrade methodology.
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Swimming Safety
Swimming not recommended, poor water quality with high algae risk
Water Quality Grade: D, Poor
Murky, only visible to about 3.4 ft. Phosphorus level: 78.3 µg/L. Trophic State Index: 63.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3.4 ft | D |
| Phosphorus | 78.3 µg/L | D |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 63 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Water Quality Trend: ↑ Improving
Based on 4 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.41 m/yr | 4 |
| Phosphorus | ↑ Improving | -63.67 µg/L/yr | 4 |
Location
County Ranking
Ranked #42 of 95 lakes in Hennepin County
Cleaner Lakes Within 30 Miles
Thomas Lake holds Grade D. One nearby lake has a higher grade.
See full comparison →Nearby Lakes in Hennepin County
More Minnesota Lake Rankings
State Parks Near Thomas Lake
Other Grade D Lakes in Minnesota
Eutrophic Lakes in Minnesota
EPA Impairment Status
Thomas 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 MN27-0149-00 · Official waterbody report · Matched by proximity (1.38 km)
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: 2022-09-20
Monitoring stations: 1