South Twin Lake

South Twin Lake comes in at a B on the grading rubric — a respectable showing for a Minnesota lake of its size and depth. The three sub-grades — clarity, phosphorus, and chlorophyll-a — track close together, so no single parameter is dragging the average.

A TSI value of 39 puts South Twin Lake in the oligotrophic range, where biological productivity stays low and the water column remains clear. A maximum depth of 40 ft puts South Twin Lake in the middle of Minnesota's depth distribution. At 141 acres, South Twin Lake fits the Minnesota median for monitored lakes, with 2.9 miles of shoreline. Within Itasca County's 141 graded lakes, South Twin Lake ranks 85 — below the local median, though not at the bottom.

Eurasian watermilfoil is established at South Twin Lake, which can dampen recreational access and pressure the native plant community. Walleye are documented at South Twin Lake, one of 13 fish species on record for the lake. The lake lacks a documented public access point, so visitor use is limited. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.