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LakeQuality
A

Bass Lake

St. Croix County, WisconsinOligotrophic

Bass Lake earns an A — water clarity, phosphorus, and chlorophyll-a all rate among the best monitored waters in St. Croix County. Sub-grades cluster within a single letter of each other, which usually means the lake is in stable trophic balance rather than fighting one specific stressor.

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. Within St. Croix County's 7 graded waters, Bass Lake sits at rank 1, near the top of the local distribution.

No invasive species are currently listed at Bass Lake — the lake remains off the Wisconsin infested-waters roster. The state fisheries records do not list documented species for Bass 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 2025-09-08. 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 31.2 ft down. Phosphorus level: 14 µg/L. Trophic State Index: 35.

MetricValueGrade
Water Clarity (Secchi Depth)31.2 ftA
Phosphorus14 µg/LA
Chlorophyll-a (Algae)No data
Trophic State Index (TSI)35Oligotrophic

Low nutrients, clear water, excellent for swimming

Water Quality Trend: Improving

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

MetricTrendChange/YearYears
Water Clarity Stable-0.09 m/yr7
Phosphorus Improving-0.8 µg/L/yr6
See year-by-year chart →

Location

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County Ranking

Ranked #1 of 7 lakes in St. Croix County

Nearby Lakes in St. Croix County

Data Sources

Water quality data from the EPA Water Quality Portal

Grading methodology based on Metropolitan Council standards

Most recent sample: 2025-09-08

Monitoring stations: 2