Updated August 2026
Safest Lakes to Swim in Minnesota
Rainy Lake (Cass County) ranks #1 for swimming in Minnesota — grade A water with low algae and public access. Below: the top 25 lakes in Minnesotathat pass our swim-safety filter.
- Grade A–B water quality
- Chlorophyll-a below 10 µg/L
Best-for-swimming on LakeGrade weights water clarity heavily: a swimmer cares whether they can see their feet, whether the water looks inviting on a 90-degree July day, and whether there is a real harmful-algal-bloom risk. The top Minnesota swimming lake on current data is Rainy Lake (A).
The swimming-best list filters more aggressively on chlorophyll-a than the cleanest list — even very clear lakes can have harmful-algal-bloom risk under specific conditions, so the swimming ranking is more conservative on that front.
| Rank | Lake | County | Grade | Swim Safety | Clarity | Algae | Phosphorus | Area |
|---|---|---|---|---|---|---|---|---|
| 1 | Rainy Lake | Cass | A | Low algae | 13.9 ft | 1.8 µg/L | 11.5 µg/L | 129 acres |
| 2 | Crane Lake | Otter Tail | A | Low algae | 9 ft | 6.4 µg/L | 15 µg/L | 350 acres |
| 3 | Lobster Lake | Douglas | A | Low algae | 13 ft | 3.6 µg/L | 20.5 µg/L | 1,334 acres |
| 4 | East Fox Lake | Crow Wing | A | Low algae | 16.4 ft | 2.7 µg/L | 10 µg/L | 241 acres |
| 5 | Deep Portage Lake | Cass | A | Low algae | 15.4 ft | 1.6 µg/L | 9 µg/L | 129 acres |
| 6 | Clearwater Lake | Cook | A | Low algae | 29 ft | 1.3 µg/L | 4 µg/L | 462 acres |
| 7 | Clearwater Lake | Wright | A | Low algae | 9.8 ft | 6.3 µg/L | 22 µg/L | 3,187 acres |
| 8 | Clearwater Lake | Clearwater | A | Low algae | 10 ft | 3.2 µg/L | 16 µg/L | 999 acres |
| 9 | Lower Hay Lake | Crow Wing | A | Low algae | 18.5 ft | 2.7 µg/L | 13 µg/L | 700 acres |
| 10 | Latoka Lake | Douglas | A | Low algae | 19 ft | 2.2 µg/L | 11 µg/L | 767 acres |
| 11 | Little Birch Lake | Todd | A | Low algae | 13 ft | 3.1 µg/L | 19 µg/L | 839 acres |
| 12 | North Long Lake | Crow Wing | A | Low algae | 15.1 ft | 2.7 µg/L | 14 µg/L | 6,190 acres |
| 13 | Bad Medicine Lake | Becker | A | Low algae | 25 ft | 1.6 µg/L | 6 µg/L | 803 acres |
| 14 | Mud Lake | Becker | A | Low algae | 12.5 ft | 5.9 µg/L | 22 µg/L | 1,178 acres |
| 15 | Big Lake | Beltrami | A | Low algae | 9.7 ft | 4.8 µg/L | 15 µg/L | 3,598 acres |
| 16 | Big Lake | Carlton | A | Low algae | 10 ft | 3.2 µg/L | 13.5 µg/L | 526 acres |
| 17 | Big Lake | Sherburne | A | Low algae | 13.6 ft | 6.1 µg/L | 10.5 µg/L | 254 acres |
| 18 | Big Sugar Bush Lake | Becker | A | Low algae | 16.5 ft | 2.7 µg/L | 10 µg/L | 522 acres |
| 19 | Pelican Lake | Otter Tail | A | Low algae | 16.4 ft | 3 µg/L | 15 µg/L | 3,962 acres |
| 20 | Pelican Lake | Crow Wing | A | Low algae | 14.3 ft | 2.7 µg/L | 11 µg/L | 8,367 acres |
| 21 | Fullers Lake: East Basin | Beltrami | A | Low algae | 15 ft | 2.4 µg/L | 10 µg/L | - |
| 22 | Birch Lake | Ramsey | A | Low algae | 5.9 ft | 3.3 µg/L | 21 µg/L | - |
| 23 | Birch Lake | Wright | A | Low algae | 15 ft | 4 µg/L | 17 µg/L | 100 acres |
| 24 | Birch Lake | Cass | A | Low algae | 14 ft | 4 µg/L | 12 µg/L | 1,267 acres |
| 25 | Round Lake | Aitkin | A | Low algae | 14.5 ft | 2.7 µg/L | 10 µg/L | 737 acres |
Frequently Asked Questions
What is the best lake to swim in Minnesota?
Rainy Lake in Cass County ranks #1 for swimming-safety in our 2026 Minnesota dataset, combining grade-A water clarity with low algae and public access. The full top 25 above ranks the swim-safest lakes statewide.
How do you know if a lake is safe to swim in Minnesota?
Three signals: (1) water clarity — Secchi depth above 6 feet is a strong sign of low suspended sediment and pathogens; (2) chlorophyll-a below 10 µg/L means low risk of harmful algae bloom; (3) a current grade of A or B from year-round sampling. MPCA and county health departments post seasonal advisories — always check before you swim, especially in late summer when blue-green algae bloom risk peaks.
Are lakes in Minnesota safe to swim in?
Most monitored Minnesota lakes are safe to swim in under normal conditions, but water quality varies widely. The lakes ranked above are filtered to grade A and B with chlorophyll-a below 10 µg/L — meaning they consistently test cleaner and have lower algae bloom risk than the state average. Always check posted advisories before swimming and avoid water after heavy rain (bacterial contamination spikes from runoff).
What lakes have algae blooms in Minnesota?
Algae blooms (especially blue-green / cyanobacteria) are most common in shallow, warm, nutrient-rich (eutrophic) lakes during late summer. Lakes with high phosphorus and chlorophyll-a measurements are at higher risk. The lakes on this page are filtered to exclude high-algae lakes. For the opposite list, see our most-polluted-lakes trend page.
When is it safe to swim in lakes in Minnesota?
Minnesota lakes are typically safest to swim in late spring through early summer (May–July), when water is cool and algae bloom risk is lowest. Risk rises in late summer and early fall (August–September) when warm water and accumulated nutrients drive cyanobacteria blooms. Always avoid swimming after heavy rainfall (bacterial spikes from runoff) and check current state DNR advisories the day you go.
What's the cleanest lake in Minnesota?
The single cleanest lake by combined water-quality score is featured on the Minnesota cleanest-lakes page. The lakes here are filtered specifically for swimming safety — same A/B grade requirement, plus low chlorophyll-a (active algae filter). For the broader cleanliness ranking, see /best/cleanest/mn.
Our swimming-safety filter
We don't just rank by overall grade. Lakes here have to pass three filters:
- Grade A or B overall water quality (top 40% statewide)
- Chlorophyll-a below 10 µg/L — actively low algae density, low risk of harmful blue-green blooms
- Multi-year sampling data — excludes lakes with limited sampling history (data confidence)
The Swim Safety column adds a direct bacteria signal on top of the grade: where the EPA Water Quality Portal has enough E. coli or fecal-coliform samples, we show a historical swim-safety grade (how often the lake has exceeded the safe-swimming threshold). It is a record of past testing, never a live "safe today" reading — bacteria spike fast after rain.
The ranking within the filter is by combined water-quality score (Secchi clarity + phosphorus + chlorophyll-a). Always check current MPCA advisories before swimming.
Where to swim near a Minnesota city
Looking for a lake close to home? These pages rank the safest swim lakes within driving distance of Minnesota's largest cities.
Where to stay near Minnesota swimming lakes
Book a cabin, resort, or rental near Minnesota's cleanest swim lakes — live availability and prices for your beach weekend.
Top-rated places to stay near Minnesota swim lakes
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Source: EPA National Aquatic Resource Surveys, 2026.