Updated August 2026
Safest Lakes to Swim in Wisconsin
Big Cedar Lake-North Site-Near West Bend (Washington County) ranks #1 for swimming in Wisconsin — grade A water with low algae and public access. Below: the top 25 lakes in Wisconsinthat 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 Wisconsin swimming lake on current data is Big Cedar Lake-North Site-Near West Bend (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 | Big Cedar Lake-North Site-Near West Bend | Washington | A | Low algae | 11.8 ft | 3.6 µg/L | 17.5 µg/L | 937 acres |
| 2 | Big Cedar Lake-South Site-Near West Bend | Washington | A | Low algae | 12.6 ft | 2.4 µg/L | 14.5 µg/L | 937 acres |
| 3 | Green Lake | Green Lake | A | Low algae | 13.5 ft | 4.4 µg/L | 38.1 µg/L | 7,920 acres |
| 4 | Lake Beulah | Walworth | A | Low algae | 10 ft | 2.5 µg/L | 13.4 µg/L | 812 acres |
| 5 | Okauchee Lake | Waukesha | A | Low algae | 11.5 ft | 3.9 µg/L | 18 µg/L | 1,210 acres |
| 6 | Geneva Lake | Walworth | A | Bacteria B | 21 ft | 2.1 µg/L | 13 µg/L | 5,401 acres |
| 7 | Powers Lake | Kenosha | A | Low algae | 10 ft | 3.4 µg/L | 17.2 µg/L | 451 acres |
| 8 | Lac Courte Oreilles Lake | Sawyer | A | Low algae | 12.2 ft | 1.7 µg/L | 15 µg/L | 5,139 acres |
| 9 | Whitefish Lake | Sawyer | A | Low algae | 13.5 ft | 1.6 µg/L | 14 µg/L | 800 acres |
| 10 | Round Lake | Sawyer | A | Low algae | 21.1 ft | 0.9 µg/L | 14 µg/L | 3,294 acres |
| 11 | Indian Lake | Sawyer | A | Low algae | 6.5 ft | 3.6 µg/L | 22.5 µg/L | 76 acres |
| 12 | Big Lake | Shawano | A | Low algae | 8 ft | 2.7 µg/L | 15 µg/L | - |
| 13 | Little Lac Courte Oreilles Lake | Sawyer | A | Low algae | 12 ft | 1.5 µg/L | 21 µg/L | 221 acres |
| 14 | Christner Lake | Sawyer | A | Low algae | 12 ft | 2.1 µg/L | 18.5 µg/L | 36 acres |
| 15 | Sand Lake | Barron | A | Low algae | 13 ft | 1.9 µg/L | 20 µg/L | - |
| 16 | Sand Lake | Sawyer | A | Low algae | 10 ft | 4.1 µg/L | 23.8 µg/L | 949 acres |
| 17 | Ashegon Lake | Sawyer | A | Low algae | 10.5 ft | 2.7 µg/L | 18 µg/L | 75 acres |
| 18 | Blueberry Lake | Sawyer | A | Low algae | 14.8 ft | 1.6 µg/L | 17 µg/L | 292 acres |
| 19 | Koonz Lake | Shawano | A | Low algae | 10.8 ft | 1.7 µg/L | 17 µg/L | 20 acres |
| 20 | Little Round Lake | Sawyer | A | Low algae | 17.3 ft | 1 µg/L | 12 µg/L | 179 acres |
| 21 | Osprey Lake | Sawyer | A | Low algae | 16 ft | 1.4 µg/L | 14.9 µg/L | 214 acres |
| 22 | Grindstone Lake | Sawyer | A | Low algae | 17.4 ft | 1.4 µg/L | 15 µg/L | 3,176 acres |
| 23 | Lost Lake | Sawyer | A | Low algae | 10.6 ft | 1.6 µg/L | 19.5 µg/L | 51 acres |
| 24 | Gaslyn Lake | Burnett | A | Low algae | 4.5 ft | 4.2 µg/L | 31.5 µg/L | 161 acres |
| 25 | Durphee Lake | Sawyer | A | Low algae | 8.1 ft | 3.1 µg/L | 22 µg/L | - |
Frequently Asked Questions
What is the best lake to swim in Wisconsin?
Big Cedar Lake-North Site-Near West Bend in Washington County ranks #1 for swimming-safety in our 2026 Wisconsin 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 Wisconsin?
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. WI DNR 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 Wisconsin safe to swim in?
Most monitored Wisconsin 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 Wisconsin?
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 Wisconsin?
Wisconsin 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 Wisconsin?
The single cleanest lake by combined water-quality score is featured on the Wisconsin 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/wi.
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 WI DNR advisories before swimming.
Where to swim near a Wisconsin city
Looking for a lake close to home? These pages rank the safest swim lakes within driving distance of Wisconsin's largest cities.
Where to stay near Wisconsin swimming lakes
Book a cabin, resort, or rental near Wisconsin's cleanest swim lakes — live availability and prices for your beach weekend.
Top-rated places to stay near Wisconsin swim lakes
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Source: EPA National Aquatic Resource Surveys, 2026.