Fourth Lake

Fourth Lake earns an F: 120 µg/L of phosphorus and clarity readings still being added signal heavy nutrient loading from the surrounding watershed.

Hypereutrophic conditions mean the lake is operating at the upper end of the productivity scale, with all the bloom risk that implies. 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. Within the 31 graded lakes of Chisago County, Fourth Lake sits at rank 31, near the bottom of the county list.

Fourth Lake has no invasive species recorded in Minnesota state databases as of 2020, though prevention practices still apply at all access points. The state fisheries records do not list documented species for Fourth Lake, which usually reflects a lack of formal fisheries survey work rather than an empty lake. No formal public access is documented at Fourth 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.