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C

Spruce Lake

Carlton County, MinnesotaEutrophic

Spruce Lake sits at a C on the grading scale — not impaired, not pristine, with summer measurements that vary year to year. The lake's weakest score is on Secchi depth — the water looks more turbid than its phosphorus number alone would predict.

Eutrophic conditions are the baseline here: clarity drops noticeably in late summer, and dissolved oxygen near the bottom can become a concern. 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. Spruce Lake ranks 14 of 33 in Carlton County — solidly in the upper half of the local distribution.

No invasive species are currently listed at Spruce Lake — the lake remains off the Minnesota infested-waters roster. The state fisheries records do not list documented species for Spruce Lake, which usually reflects a lack of formal fisheries survey work rather than an empty lake. No formal public access is documented at Spruce 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 2024-07-08. Grade methodology: LakeGrade methodology.

Reviewed by LakeQuality Editorial Team · Updated

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Swimming Safety

Generally safe for swimming, moderate water quality

Water Quality Grade: C, Fair

Very murky, less than 2.3 ft of visibility. Phosphorus level: 19 µg/L. Chlorophyll-a: 9.1 µg/L. Trophic State Index: 55.

MetricValueGrade
Water Clarity (Secchi Depth)2.3 ftF
Phosphorus19 µg/LA
Chlorophyll-a (Algae)9.1 µg/LB
Trophic State Index (TSI)55Eutrophic

High nutrients, frequent algae, reduced clarity

Water Quality Trend: Improving

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

MetricTrendChange/YearYears
Water Clarity Improving+0.453 m/yr5
Phosphorus Declining+2 µg/L/yr2
Chlorophyll-a Improving-0.46 µg/L/yr5
See year-by-year chart →

Location

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County Ranking

Ranked #14 of 33 lakes in Carlton County

Cleaner Lakes Within 30 Miles

Spruce Lake holds Grade C. 2 nearby lakes hold higher grades.

See full comparison →

Nearby Lakes in Carlton County

EPA Impairment Status

Spruce 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_121 · Official waterbody report · Matched by proximity (0 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: 2024-07-08

Monitoring stations: 1