South Twin Lake

On the LakeGrade rubric, South Twin Lake pulls an A: clarity readings still being added and 12 µg/L of phosphorus put it in the top bracket for Wisconsin.

A TSI value of 40 puts South Twin Lake in the oligotrophic range, where biological productivity stays low and the water column remains clear. The lake's maximum depth is not yet documented in state morphometric records — context for its physical structure remains limited. South Twin Lake covers 639 acres alongside partial shoreline records — a mid-sized water that supports a working fishery without being so large that conditions diverge between basins. Within Polk County's 73 graded waters, South Twin Lake sits at rank 7, near the top of the local distribution.

No invasive species are currently listed at South Twin Lake — the lake remains off the Wisconsin infested-waters roster. The state fisheries records do not list documented species for South Twin Lake, which usually reflects a lack of formal fisheries survey work rather than an empty lake. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.