North Union Lake

On the LakeGrade rubric, North Union Lake pulls an A: clarity at 20.3 ft and 14 µg/L of phosphorus put it in the top bracket for Minnesota. The three sub-grades — clarity, phosphorus, and chlorophyll-a — track close together, so no single parameter is dragging the average.

A TSI value of 38 puts North Union Lake in the oligotrophic range, where biological productivity stays low and the water column remains clear. North Union Lake reaches 42 ft at its deepest point — typical for Minnesota mid-sized lakes, with seasonal stratification but limited cold-water refuge. At 118 acres, North Union Lake fits the Minnesota median for monitored lakes, with 4.1 miles of shoreline. Among the 51 graded lakes in Douglas County, North Union Lake sits at rank 14, above the county median.

Zebra mussel presence at North Union Lake means the lake's clarity numbers carry an asterisk — filtered water is not the same as nutrient-poor water. Walleye are documented at North Union Lake, one of 13 fish species on record for the lake. No formal public access is documented at North Union Lake — most use is by shoreline residents and their guests. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.