Are Minnesota Lakes Cleaner Than Wisconsin Lakes?
Minnesota and Wisconsin lakes are roughly comparable on average water quality. Minnesota's monitored lakes average grade C (2.30); Wisconsin averages grade B (3.36). The differences are regional — the Boundary Waters and Brainerd Lakes areas in MN have exceptional clarity, while the Northwoods of WI is comparable. Agricultural Minnesota (the southern half) and the Fox-Wolf system in Wisconsin both struggle with phosphorus enrichment.
Direct comparison
The numbers from our monitoring dataset:
- Average grade: MN C (2.30) vs WI B (3.36)
- Lakes monitored: MN 2,248 vs WI 1,522
- Grade A lakes: MN 657 (29%) vs WI 1,040 (68%)
- Grade F lakes: MN 281 vs WI 29
- Improving lakes: MN 657 vs WI 577
- Declining lakes: MN 677 vs WI 391
Where Minnesota wins
The Boundary Waters Canoe Area Wilderness (Cook, Lake, and St. Louis Counties) contains some of the cleanest large lakes anywhere in the Lower 48. The Brainerd Lakes area, Detroit Lakes area, and the Itasca/Bemidji headwaters region are all nationally exceptional. Minnesota's deep, glacially-carved northern lakes generally outperform shallower Wisconsin counterparts.
Where Wisconsin wins
The Northwoods (Vilas, Oneida, Forest Counties) holds dense concentrations of small, clean kettle lakes — many grade A. Wisconsin's investment in shoreland zoning and runoff control over the past two decades has produced more "improving" trend lakes per capita than Minnesota.
Where both struggle
Agricultural watersheds dominated by row-crop farming (southern MN, the Fox-Wolf basin in WI, the Driftless Area where intensive ag meets karst geology) have the worst water quality. Phosphorus from fertilizer runoff is the dominant problem in both states.