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B

Pat Martin Lake

Carlton County, MinnesotaMesotrophic

Pat Martin Lake carries a solid B grade — strong on most parameters, with measurements that hold up well across the summer season. The lake's weakest score is on Secchi depth — the water looks more turbid than its phosphorus number alone would predict.

A TSI near 45 places Pat Martin Lake in the mesotrophic band — moderate productivity, with seasonal swings between clearer spring water and richer late-summer conditions. 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 33 graded lakes in Carlton County, Pat Martin Lake ranks 3 — in the top quartile locally.

Pat Martin 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 Pat Martin Lake, which usually reflects a lack of formal fisheries survey work rather than an empty lake. No formal public access is documented at Pat Martin 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 2024-10-03. 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 6.6 ft. Phosphorus level: 15 µg/L. Chlorophyll-a: 3.5 µg/L. Trophic State Index: 45.

MetricValueGrade
Water Clarity (Secchi Depth)6.6 ftC
Phosphorus15 µg/LA
Chlorophyll-a (Algae)3.5 µg/LA
Trophic State Index (TSI)45Mesotrophic

Moderate nutrients, good water quality

Water Quality Trend: Improving

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

MetricTrendChange/YearYears
Water Clarity Improving+1.123 m/yr5
Phosphorus Declining+2 µg/L/yr2
Chlorophyll-a Improving-0.47 µg/L/yr5
See year-by-year chart →

Location

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County Ranking

Ranked #3 of 33 lakes in Carlton County

Nearby Lakes in Carlton County

EPA Impairment Status

Pat Martin 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_113 · 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