Shannon Lake

On the LakeGrade rubric, Shannon Lake pulls an A: clarity at 24.6 ft and 19 µg/L of phosphorus put it in the top bracket for Wisconsin. Clarity, phosphorus, and chlorophyll-a all rate similarly, so there is no obvious single lever to pull on watershed management.

A TSI value of 39 puts Shannon Lake in the oligotrophic range, where biological productivity stays low and the water column remains clear. The lake bottoms out at 37 ft — a moderate depth that supports a warm-water fishery without the year-round cold refuge a deeper basin provides. Shannon Lake is small — 58 acres alongside partial shoreline records — which makes it sensitive to even modest changes in watershed runoff or recreational pressure. Within Marinette County's 22 graded lakes, Shannon Lake ranks 13 — below the local median, though not at the bottom.

Shannon Lake has no invasive species recorded in Wisconsin state databases as of 2022, though prevention practices still apply at all access points. The lake's fish records list 1 species — a varied community without one dominant gamefish. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.