Published April 7, 2026 · Updated annually
Best Lakes for Swimming in Minnesota & Wisconsin (2026)
Out of 3,770 monitored lakes across Minnesota and Wisconsin, these 15 earn the highest water quality grades. Each is graded A or B based on EPA Water Quality Portal data measuring water clarity, phosphorus concentration, and algae levels — the three factors that matter most for safe swimming.
Top 15 Lakes for Swimming
| Rank | Lake | State | County | Grade | Clarity (ft) | Area |
|---|---|---|---|---|---|---|
| 1 | East Fox Lake | MN | Crow Wing | A | 16.1 | 240.88 acres |
| 2 | Deep Portage Lake | MN | Cass | A | 15.4 | 129.02 acres |
| 3 | Little Wabana Lake | MN | Itasca | A | 23.8 | 115.73 acres |
| 4 | Clearwater Lake | MN | Cook | A | 30 | 461.73 acres |
| 5 | Clearwater Lake | MN | Lake | A | 18 | 640.18 acres |
| 6 | Lower Hay Lake | MN | Crow Wing | A | 19 | 700.21 acres |
| 7 | Latoka Lake | MN | Douglas | A | 19 | 766.63 acres |
| 8 | Bad Medicine Lake | MN | Becker | A | 25 | 803.03 acres |
| 9 | Big Sugar Bush Lake | MN | Becker | A | 17 | 521.51 acres |
| 10 | Pelican Lake | MN | Otter Tail | A | 16.1 | 4.0K acres |
| 11 | Fullers Lake: East Basin | MN | Beltrami | A | 49.2 | — |
| 12 | Birch Lake | MN | Wright | A | 15 | 99.82 acres |
| 13 | Birch Lake | MN | Cook | A | 18 | 236.31 acres |
| 14 | Birch Lake | MN | Unknown | A | 15 | 836.35 acres |
| 15 | Round Lake | MN | Aitkin | A | 15.3 | 634.03 acres |
What Makes a Lake Safe for Swimming?
Water quality grades reflect three core measurements that directly impact swimming safety:
- Secchi depth (water clarity) — How far you can see into the water. The top-graded lakes have clarity exceeding 15 feet, meaning you can see the bottom in many areas. High clarity means low algae and low suspended sediment.
- Phosphorus levels — The nutrient that feeds algae growth. Lakes graded A have phosphorus below 20 micrograms per liter. Higher phosphorus means more algae blooms, including potentially toxic cyanobacteria (blue-green algae).
- Chlorophyll-a — A direct measure of algae concentration. Top-rated swimming lakes have chlorophyll-a below 5 micrograms per liter, indicating minimal algae presence.
Why These Lakes Stand Out
The lakes on this list share common characteristics: they tend to be deeper (reducing warm-water algae growth), have forested or protected watersheds (less nutrient runoff), and benefit from geological features like sandy or rocky bottoms that limit phosphorus release from sediments.
Minnesota and Wisconsin are home to thousands of lakes, but water quality varies dramatically. A lake graded A may have crystal-clear water with 20+ feet of visibility, while an F-graded lake a few miles away could have visibility under 3 feet with frequent algae blooms.
Swimming Safety Tips
- Check the lake's current grade on LakeGrade before heading out
- Avoid swimming after heavy rain — runoff temporarily increases bacteria and nutrient levels
- If you see green scum or discolored water, stay out — it may indicate a harmful algae bloom
- Deeper water away from shore is generally cleaner than shallow nearshore areas
- Check your state's beach monitoring program for real-time advisories
Frequently Asked Questions
Based on EPA monitoring data, the highest-graded lakes in Minnesota earn an A for water clarity, low phosphorus, and minimal algae. See the full table above for the current top 15 across both states.
Most Wisconsin lakes are safe for swimming. Lakes graded A or B have excellent water quality. Lakes graded C are generally safe but may have moderate algae during warm months. Avoid swimming in lakes graded D or F, which may have harmful algae blooms.
Lake water quality is measured using three key indicators: secchi depth (water clarity), total phosphorus (nutrient levels), and chlorophyll-a (algae concentration). These measurements come from the EPA Water Quality Portal and state monitoring programs.
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