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. Clarity, phosphorus, and chlorophyll-a all rate similarly, so there is no obvious single lever to pull on watershed management.

The hypereutrophic status — TSI 73 — reflects sustained heavy nutrient loading from the surrounding watershed and frequent algal pressure. 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. Fourth Lake ranks 31 of 31 in Chisago County — at the lower end of the locally monitored distribution.

No invasive species are currently listed at Fourth Lake — the lake remains off the Minnesota infested-waters roster. 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. 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.