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.

Mesotrophic conditions dominate at Grand Portage Lake: enough nutrients for a healthy fishery, not so much that algal blooms become a chronic problem. 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. Among the 33 graded lakes in Iron County, Grand Portage Lake ranks 4 — in the top quartile locally.

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.