Question 1

What is the best lake to swim in Wisconsin?

Accepted Answer

Geneva Lake in Walworth 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.

Question 2

How do you know if a lake is safe to swim in Wisconsin?

Accepted Answer

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.

Question 3

Are lakes in Wisconsin safe to swim in?

Accepted Answer

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).

Question 4

What lakes have algae blooms in Wisconsin?

Accepted Answer

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.

Question 5

When is it safe to swim in lakes in Wisconsin?

Accepted Answer

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.

Question 6

What's the cleanest lake in Wisconsin?

Accepted Answer

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.

Rank	Lake	County	Grade	Clarity	Algae	Phosphorus	Area
1	Geneva Lake	Walworth	A	19 ft	—	13 µg/L	5.4K acres
2	Lac Courte Oreilles Lake	Sawyer	A	38.7 ft	1.4 µg/L	16 µg/L	5.1K acres
3	Sunset Lake	Portage	A	41 ft	—	12 µg/L	63 acres
4	Sunset Lake	Vilas	A	56.5 ft	—	11 µg/L	207 acres
5	Grindstone Lake	Sawyer	A	57.7 ft	1.7 µg/L	14.4 µg/L	3.2K acres
6	Middle Sugarbush Lake	Vilas	A	50 ft	—	13 µg/L	254 acres
7	Irving Lake	Vilas	A	36.1 ft	—	18.6 µg/L	419 acres
8	Windigo Lake	Sawyer	A	36.1 ft	—	15.6 µg/L	503 acres
9	Towanda Lake	Vilas	A	34.5 ft	—	12.6 µg/L	139 acres
10	Parker Lake	Adams	A	55.8 ft	—	14.8 µg/L	57 acres
11	West Bay Lake	Vilas	A	42.7 ft	—	16.4 µg/L	417 acres
12	Long Lake	Washburn	A	29.5 ft	—	17.5 µg/L	-
13	Long Lake	Waushara	A	45.9 ft	—	11.6 µg/L	254 acres
14	Long Lake	Waupaca	A	44.3 ft	—	12.4 µg/L	112 acres
15	Long Lake	Burnett	A	68.9 ft	—	11.3 µg/L	222 acres
16	Long Lake	Lincoln	A	47.7 ft	—	12.4 µg/L	119 acres
17	Long Lake	Chippewa	A	32.8 ft	—	12.4 µg/L	936 acres
18	Long Lake	Fond du Lac	A	32.8 ft	—	19.3 µg/L	423 acres
19	Long Lake	Bayfield	A	52.5 ft	—	13.7 µg/L	280 acres
20	Long Lake	Oconto	A	47.6 ft	—	10.2 µg/L	-
21	Chain Lake	Oconto	A	44.3 ft	—	9.5 µg/L	76 acres
22	Upper Eau Claire Lake	Bayfield	A	61.5 ft	—	11.5 µg/L	1.0K acres
23	Spring Lake	Vilas	A	27.9 ft	—	16.3 µg/L	236 acres
24	Spring Lake	Manitowoc	A	26.2 ft	—	19.6 µg/L	9 acres
25	Black Hawk Lake	Iowa	A	17.2 ft	—	19.9 µg/L	212 acres

Best Swimming Lakes in Wisconsin

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