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B

Horseleg Lake

Isanti County, MinnesotaMesotrophic

On the LakeGrade scale Horseleg Lake grades a B, with clarity at 3.7 ft and 17 µg/L of phosphorus placing it above the Minnesota median. Secchi readings are the weakest of the scored parameters, suggesting suspended sediment or algal biomass dominates the optical signal.

Mesotrophic conditions dominate at Horseleg Lake: enough nutrients for a healthy fishery, not so much that algal blooms become a chronic problem. 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. Horseleg Lake ranks 6 of 19 in Isanti County — solidly in the upper half of the local distribution.

No invasive species are currently listed at Horseleg Lake — the lake remains off the Minnesota infested-waters roster. The state fisheries records do not list documented species for Horseleg Lake, which usually reflects a lack of formal fisheries survey work rather than an empty lake. No formal public access is documented at Horseleg Lake — most use is by shoreline residents and their guests. 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 2024-09-18. 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 3.7 ft. Phosphorus level: 17 µg/L. Chlorophyll-a: 4 µg/L. Trophic State Index: 49.

MetricValueGrade
Water Clarity (Secchi Depth)3.7 ftD
Phosphorus17 µg/LA
Chlorophyll-a (Algae)4 µg/LA
Trophic State Index (TSI)49Mesotrophic

Moderate nutrients, good water quality

Water Quality Trend: Declining

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

MetricTrendChange/YearYears
Water Clarity Declining-0.731 m/yr5
Phosphorus Declining+0.75 µg/L/yr5
Chlorophyll-a Improving-1.3 µg/L/yr2
See year-by-year chart →

Location

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County Ranking

Ranked #6 of 19 lakes in Isanti County

Cleaner Lakes Within 30 Miles

Horseleg Lake holds Grade B. 2 nearby lakes hold higher grades.

See full comparison →

Nearby Lakes in Isanti County

EPA Impairment Status

Horseleg Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).

Causes of impairment

Nutrients (phosphorus, nitrogen)

Source: EPA ATTAINS assessment unit MN30-0004-00 · Official waterbody report · Matched by proximity (2.61 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: 2024-09-18

Monitoring stations: 1