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B

Pirz Lake

Stearns County, MinnesotaMesotrophic

Pirz Lake carries a solid B grade — strong on most parameters, with measurements that hold up well across the summer season. The two scored sub-grades — clarity and phosphorus — track close together, so neither one is dragging the average down.

A TSI near 46 places Pirz 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. Within Stearns County's 55 graded waters, Pirz Lake sits at rank 13, near the top of the local distribution.

No invasive species are currently listed at Pirz Lake — the lake remains off the Minnesota infested-waters roster. The state fisheries records do not list documented species for Pirz Lake, which usually reflects a lack of formal fisheries survey work rather than an empty lake. The lake lacks a documented public access point, so visitor use is limited. The lake has a partial ice record — 5 observed ice-outs, centered near Apr 9. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.

Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-09-22. 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

Good clarity, visible to about 11.2 ft. Phosphorus level: 25 µg/L. Trophic State Index: 46.

MetricValueGrade
Water Clarity (Secchi Depth)11.2 ftB
Phosphorus25 µg/LB
Chlorophyll-a (Algae)No data
Trophic State Index (TSI)46Mesotrophic

Moderate nutrients, good water quality

Water Quality Trend: Declining

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

MetricTrendChange/YearYears
Water Clarity Declining-0.419 m/yr5
Phosphorus Declining+0.95 µg/L/yr5
See year-by-year chart →

Ice Season

Historical ice data from Minnesota DNR (8 observations).

Typical Ice-Out
Apr 9
Typical Ice-In
Dec 1

Estimated open water season: 236 days

EarliestLatest
Ice-Out2016-03-15 (2016)2018-04-30 (2018)
Ice-In2006-11-30 (2006)2017-12-09 (2017)

Most recent ice-out: 2018-04-30

Location

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County Ranking

Ranked #13 of 55 lakes in Stearns County

Nearby Lakes in Stearns County

State Parks Near Pirz Lake

DNR Reports & Resources

Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Pirz Lake. 1 report on file.

EPA Impairment Status

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

Causes of impairment

MercuryNutrients (phosphorus, nitrogen)Salinity / chlorides

A Total Maximum Daily Load (TMDL) plan has been approved.

Source: EPA ATTAINS assessment unit MN73-0196-00 · Official waterbody report · Matched by proximity (2.6 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

Ice data from Minnesota DNR Climate

Most recent sample: 2024-09-22

Monitoring stations: 1