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Twin Lake

Washington County, MinnesotaMesotrophic

On the LakeGrade rubric, Twin Lake pulls an A: clarity at 13.0 ft and 13 µg/L of phosphorus put it in the top bracket for Minnesota. Clarity, phosphorus, and chlorophyll-a all rate similarly, so there is no obvious single lever to pull on watershed management.

A TSI near 41 places Twin 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 Washington County's 83 graded waters, Twin Lake sits at rank 5, near the top of the local distribution.

Twin 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 Twin Lake, which usually reflects a lack of formal fisheries survey work rather than an empty lake. No formal public access is documented at Twin 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 2024-10-14. Grade methodology: LakeGrade methodology.

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Swimming Safety

Excellent for swimming, crystal clear water with minimal algae

Water Quality Grade: A, Excellent

Good clarity, visible to about 13 ft. Phosphorus level: 13 µg/L. Chlorophyll-a: 2.8 µg/L. Trophic State Index: 41.

MetricValueGrade
Water Clarity (Secchi Depth)13 ftB
Phosphorus13 µg/LA
Chlorophyll-a (Algae)2.8 µg/LA
Trophic State Index (TSI)41Mesotrophic

Moderate nutrients, good water quality

Water Quality Trend: Stable

Based on 6 years of monitoring data (2020-2025).

MetricTrendChange/YearYears
Water Clarity Stable-0.083 m/yr6
See year-by-year chart →

Location

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County Ranking

Ranked #5 of 83 lakes in Washington County

Nearby Lakes in Washington County

EPA Impairment Status

Twin Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).

Causes of impairment

Mercury

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

Source: EPA ATTAINS assessment unit MN82-0049-00 · Official waterbody report · Matched by proximity (1.78 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: 2024-10-14

Monitoring stations: 1