Best Swimming Lakes in Wisconsin
Axehead Lake (Cook County) ranks #1 for swimming in Wisconsin — grade A water with low algae and public access. Below: the top 17 lakes in Wisconsinthat pass our swim-safety filter (grade A/B, chlorophyll-a below 10 µg/L).
Swimming-friendly is a clarity-plus-algae problem: clear water and a low chlorophyll-a number. Axehead Lake (A) tops the Illinois list on those combined measures.
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 | Clarity | Algae | Phosphorus | Area |
|---|---|---|---|---|---|---|---|
| 1 | Axehead Lake | Cook | A | 11.9 ft | — | 10 µg/L | - |
| 2 | Powderhorn Lake | Cook | A | 10.1 ft | — | 13 µg/L | - |
| 3 | Baumann Park Lake | Winnebago | A | 10.2 ft | — | 11.5 µg/L | - |
| 4 | Silver Lake | McHenry | B | 7 ft | — | 11 µg/L | - |
| 5 | Boulder South Lake | Perry | B | 8.8 ft | — | 14.5 µg/L | - |
| 6 | Wampum Lake | Cook | B | 6.9 ft | — | 16 µg/L | - |
| 7 | Big Rock Lake | Kane | B | 8.1 ft | — | 10 µg/L | - |
| 8 | Round Lake | Lake | B | 7.4 ft | — | 19.5 µg/L | 242 acres |
| 9 | One Horse Gap Lake | Pope | B | 4 ft | — | 17 µg/L | 29 acres |
| 10 | Flatfoot Lake | Cook | B | 6.3 ft | — | 10.5 µg/L | - |
| 11 | Opeka Lake | Cook | B | 3.9 ft | — | 15.5 µg/L | - |
| 12 | Glendale Lake | Pope | B | 4.8 ft | — | 16 µg/L | 84 acres |
| 13 | Tecumseh Lake | Hardin | B | 3.6 ft | — | 18 µg/L | 13 acres |
| 14 | Grays Lake | Lake | B | 3.5 ft | — | 18 µg/L | - |
| 15 | Calumet Lake | Cook | B | 4.3 ft | — | 10.5 µg/L | 0 acres |
| 16 | Lily Lake | McHenry | B | 3.3 ft | — | 16 µg/L | - |
| 17 | Catherine Lake | Lake | B | 7.4 ft | — | 27.5 µg/L | - |
Frequently Asked Questions
What is the best lake to swim in Wisconsin?
Axehead Lake in Cook 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. Wisconsin 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 ranking within the filter is by combined water-quality score (Secchi clarity + phosphorus + chlorophyll-a). Always check current Wisconsin DNR advisories before swimming.
Source: EPA National Aquatic Resource Surveys, 2026.