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LakeQuality
F

Grass Lake

Hennepin County, MinnesotaLimited DataHypereutrophic

On the LakeGrade rubric Grass Lake fails the cutoffs — a TSI of 76 and persistent algal pressure put it in the bottom tier. Sub-grades cluster within a single letter of each other, which usually means the lake is in stable trophic balance rather than fighting one specific stressor.

Hypereutrophic conditions mean the lake is operating at the upper end of the productivity scale, with all the bloom risk that implies. 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. Grass Lake ranks 88 of 95 in Hennepin County — at the lower end of the locally monitored distribution.

Grass 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 Grass Lake, which usually reflects a lack of formal fisheries survey work rather than an empty lake. No formal public access is documented at Grass Lake — most use is by shoreline residents and their guests. Ice-out has been recorded 6 times at Grass Lake, with a median around Mar 30. 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 2022-10-12. Grade methodology: LakeGrade methodology.

Swimming Safety

Avoid swimming, very poor water quality, potential algae toxins

Water Quality Grade: F, Very Poor

No clarity data. Phosphorus level: 148 µg/L. Trophic State Index: 76.

MetricValueGrade
Water Clarity (Secchi Depth)No data
Phosphorus148 µg/LF
Chlorophyll-a (Algae)No data
Trophic State Index (TSI)76Hypereutrophic

Very high nutrients, dense algae, poor clarity

Water Quality Trend: Declining

Based on 2 years of monitoring data (2020-2025).

MetricTrendChange/YearYears
Phosphorus Declining+28 µg/L/yr2

Ice Season

Historical ice data from Minnesota DNR (9 observations).

Typical Ice-Out
Mar 30
EarliestLatest
Ice-Out2024-03-04 (2024)2023-04-11 (2023)
Ice-In2017-12-08 (2017)2024-01-03 (2024)

Most recent ice-out: 2024-03-04

Location

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County Ranking

Ranked #88 of 95 lakes in Hennepin County

Nearby Lakes in Hennepin County

Hypereutrophic Lakes in Minnesota

Data Sources

Water quality data from the EPA Water Quality Portal

Grading methodology based on Metropolitan Council standards

Ice data from Minnesota DNR Climate

Most recent sample: 2022-10-12

Monitoring stations: 1