Grand Portage Lake

Grand Portage Lake sits at the top of the Wisconsin DNR grading rubric with an A, a mark reached by the cleanest lakes in Wisconsin. 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 value of 33 puts Grand Portage Lake in the oligotrophic range, where biological productivity stays low and the water column remains clear. A maximum depth of 33 ft puts Grand Portage Lake in the middle of Wisconsin's depth distribution. At 148 acres, Grand Portage Lake fits the Wisconsin median for monitored lakes, with partial shoreline records. Grand Portage Lake ranks 15 of 34 in Iron County — solidly in the upper half of the local distribution.

Grand Portage Lake carries an invasive watermilfoil record — boat-launch decontamination and shoreline care matter more here than at uninfested lakes. The fishery includes walleye alongside the lake's other 6 documented species — a notable draw for Wisconsin anglers. Public access is available — the lake is on the Wisconsin DNR public-access list. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.