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LakeQuality
A

Big Lake

Vilas County, WisconsinOligotrophic

Big Lake sits at the top of the Wisconsin DNR grading rubric with an A, a mark reached by the cleanest lakes in Wisconsin. Clarity, phosphorus, and chlorophyll-a all rate similarly, so there is no obvious single lever to pull on watershed management.

The lake's low TSI puts it in oligotrophic territory — the cleanest of the four trophic classes, but also the most vulnerable to nutrient-driven shifts. 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. Big Lake ranks 16 of 202 in Vilas County, putting it in the upper tier of locally monitored lakes.

No invasive species are currently listed at Big Lake — the lake remains off the Wisconsin infested-waters roster. The state fisheries records do not list documented species for Big Lake, which usually reflects a lack of formal fisheries survey work rather than an empty lake. Monitoring depth is thin here: the LakeGrade rubric is applied to a small number of sample years, and the grade will be revised as more data accumulates.

Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2025-08-26. Grade methodology: LakeGrade methodology.

Swimming Safety

Excellent for swimming, crystal clear water with minimal algae

Water Quality Grade: A, Excellent

Crystal clear, you can see 39.4 ft down. Phosphorus level: 12.8 µg/L. Trophic State Index: 33.

MetricValueGrade
Water Clarity (Secchi Depth)39.4 ftA
Phosphorus12.8 µg/LA
Chlorophyll-a (Algae)No data
Trophic State Index (TSI)33Oligotrophic

Low nutrients, clear water, excellent for swimming

Water Quality Trend: Stable

Based on 7 years of monitoring data (2020-2025).

MetricTrendChange/YearYears
Water Clarity Stable+0.018 m/yr7
Phosphorus Stable-0.22 µg/L/yr6
See year-by-year chart →

Location

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County Ranking

Ranked #16 of 202 lakes in Vilas County

Nearby Lakes in Vilas County

Data Sources

Water quality data from the EPA Water Quality Portal

Grading methodology based on Metropolitan Council standards

Most recent sample: 2025-08-26

Monitoring stations: 3