Deep Lakes in Minnesota & Wisconsin
Lakes over 50 feet deep in Minnesota and Wisconsin. Deep lakes maintain cold, oxygenated water below the thermocline year-round, supporting coldwater species like lake trout, cisco, and whitefish.
Maximum-depth data currently comes from the Minnesota and Wisconsin DNR lake surveys, so these rankings cover MN and WI lakes only. Grades for the other 10 covered states are based on clarity and nutrient measurements.
| Rank | Lake | County | State | Grade | Depth | Area | Fish |
|---|---|---|---|---|---|---|---|
| 1 | Gilbert Pit Lake | St. Louis | MN | NR | 443 ft | 243 acres | 10 |
| 2 | St James Pit Lake | St. Louis | MN | NR | 381 ft | 124 acres | 5 |
| 3 | Wazee Lake | Jackson | WI | NR | 350 ft | 146 acres | 0 |
| 4 | Iron Chief Complex Lake | St. Louis | MN | NR | 262.1 ft | 207 acres | 3 |
| 5 | Green Lake | Green Lake | WI | A | 236 ft | 7,920 acres | 7 |
| 6 | Green Lake | Green Lake | WI | NR | 236 ft | 7,920 acres | 7 |
Frequently Asked Questions
Why are deep lakes important for water quality?
Deep lakes maintain a thermocline (temperature barrier) that keeps bottom water cold and oxygen-rich throughout summer. This supports coldwater fish species like lake trout and cisco that cannot survive in shallower, warmer lakes. Deep lakes also resist algae blooms better because their large volume dilutes nutrients.
What is the deepest lake in Minnesota and Wisconsin?
The deepest lakes in both states exceed 200 feet. These deep lakes are typically located in geologically carved basins from glacial activity and offer some of the best water quality and coldwater fishing in the region.
Notable Deep Lakes
St. Louis County, MN · Not rated · 443 ft
St. Louis County, MN · Not rated · 381 ft
Jackson County, WI · Not rated · 350 ft
St. Louis County, MN · Not rated · 262.1 ft
Green Lake County, WI · Grade A · 236 ft
Green Lake County, WI · Not rated · 236 ft
Source: EPA National Aquatic Resource Surveys, 2026.