Cup Lake

Cup Lake earns a D — measurements through 2022 show persistent nutrient pressure that limits clarity through the summer. 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.

A TSI in the eutrophic range signals a lake doing what nutrient-loaded waters do — supporting an active algal community at the cost of clear water. 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. Among the 9 graded lakes in Big Stone County, Cup Lake ranks 2 — in the top quartile locally.

No invasive species are currently listed at Cup Lake — the lake remains off the Minnesota infested-waters roster. The state fisheries records do not list documented species for Cup Lake, which usually reflects a lack of formal fisheries survey work rather than an empty lake. No formal public access is documented at Cup Lake — most use is by shoreline residents and their guests. 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.