Best Swimming Lakes in Wisconsin: Clearest Water, Lowest Algae (2026)

Best-for-swimming on LakeQuality 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.

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	Advisories & bacteria	Clarity	Algae	Phosphorus	Area
1	Big Cedar Lake-North Site-Near West Bend	Washington	Low algae	11.8 ft	3.6 µg/L	17.5 µg/L	937 acres
2	Green Lake	Green Lake	Low algae	13.5 ft	4.4 µg/L	38.1 µg/L	7,920 acres
3	Lake Beulah	Walworth	Low algae	10 ft	2.5 µg/L	13.4 µg/L	812 acres
4	Geneva Lake	Walworth	Bacteria tested: low	21 ft	2.1 µg/L	13 µg/L	5,401 acres
5	Powers Lake	Kenosha	Low algae	10 ft	3.4 µg/L	17.2 µg/L	451 acres
6	Lac Courte Oreilles Lake	Sawyer	Low algae	12.2 ft	1.7 µg/L	15 µg/L	5,139 acres
7	Whitefish Lake	Sawyer	Low algae	13.5 ft	1.6 µg/L	14 µg/L	800 acres
8	Round Lake	Sawyer	Low algae	21.1 ft	0.9 µg/L	14 µg/L	3,294 acres
9	Indian Lake	Sawyer	Low algae	6.5 ft	3.6 µg/L	22.5 µg/L	76 acres
10	Big Lake	Shawano	Low algae	8 ft	2.7 µg/L	15 µg/L	-
11	Christner Lake	Sawyer	Low algae	12 ft	2.1 µg/L	18.5 µg/L	36 acres
12	Sand Lake	Barron	Low algae	13 ft	1.9 µg/L	20 µg/L	-
13	Sand Lake	Sawyer	Low algae	10 ft	4.1 µg/L	23.8 µg/L	949 acres
14	Ashegon Lake	Sawyer	Low algae	10.5 ft	2.7 µg/L	18 µg/L	75 acres
15	Blueberry Lake	Sawyer	Low algae	14.8 ft	1.6 µg/L	17 µg/L	292 acres
16	Koonz Lake	Shawano	Low algae	10.8 ft	1.7 µg/L	17 µg/L	20 acres
17	Little Round Lake	Sawyer	Low algae	17.3 ft	1 µg/L	12 µg/L	179 acres
18	Osprey Lake	Sawyer	Low algae	16 ft	1.4 µg/L	14.9 µg/L	214 acres
19	Grindstone Lake	Sawyer	Low algae	17.4 ft	1.4 µg/L	15 µg/L	3,176 acres
20	Lost Lake	Sawyer	Low algae	10.6 ft	1.6 µg/L	19.5 µg/L	51 acres
21	Gaslyn Lake	Burnett	Low algae	4.5 ft	4.2 µg/L	31.5 µg/L	161 acres
22	Durphee Lake	Sawyer	Low algae	8.1 ft	3.1 µg/L	22 µg/L	-
23	Malone Lake	Shawano	Low algae	13.5 ft	2.1 µg/L	18 µg/L	14 acres
24	Sams Lake	Shawano	Low algae	11 ft	2.2 µg/L	18 µg/L	6 acres
25	Oneida Lake	Outagamie	Low algae	—	1.4 µg/L	15 µg/L	12 acres

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All-states list →Minnesota version →Illinois version →Michigan version →Cleanest lakes in Wisconsin →Swimming safety guide →Algae bloom guide →

Frequently Asked Questions

What is the best lake to swim in Wisconsin?

Big Cedar Lake-North Site-Near West Bend in Washington County ranks first for swimming in the 2026 Wisconsin sampling record, combining the clearest water with low algae and public access. The full top 25 above is ranked the same way.

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

That is a call for WI DNR and county health departments, who post seasonal and same-day advisories — always check before you swim, especially in late summer when blue-green algae bloom risk peaks. The readings on this page show what past sampling found: Secchi depth above 6 feet is a strong sign of low suspended sediment, and chlorophyll-a below 10 µg/L means a low algae load. Neither is a clearance.

Are lakes in Wisconsin safe to swim in?

Whether a given lake is safe to swim in on a given day is answered by WI DNR and the county health department, not by a water-quality reading. The lakes ranked above are filtered to the clearest, lowest-nutrient readings in the sampling record with chlorophyll-a below 10 µg/L, which means they have tested cleaner and carried less algae than the state average. Always check posted advisories before swimming and avoid water after heavy rain, when bacteria 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; each lake page shows its own phosphorus and chlorophyll-a readings.

When is it safe to swim in lakes in Wisconsin?

Algae load in Wisconsin lakes is typically lowest from late spring through early summer (May–July), when water is cool. It rises in late summer and early fall (August–September) when warm water and accumulated nutrients drive cyanobacteria blooms. Avoid swimming after heavy rainfall, when bacteria spikes from runoff, and check WI DNR's current advisories the day you go.

What's the cleanest lake in Wisconsin?

The single cleanest lake on measured clarity and nutrients leads the Wisconsin cleanest-lakes ranking, linked below. The lakes on this page are filtered for swimming — the same clarity and nutrient readings, plus low chlorophyll-a (an active algae filter).

Our swimming filter

Lakes here have to pass three filters:

Clear, low-nutrient water — the top of the state’s measured range for clarity, phosphorus and chlorophyll-a
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 Advisories & bacteria column adds a direct bacteria signal: where the EPA Water Quality Portal has enough E. coli or fecal-coliform samples, we show how often the lake has exceeded the EPA recreation threshold. It is a record of past testing, never a live "safe today" reading — bacteria spike fast after rain. Where a lake carries an EPA 303(d) bacteria or recreation listing, that advisory runs above the bacteria record in the table rather than beside it.

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 swimming lakes within driving distance of Wisconsin's largest cities.

Swim near Milwaukee →Swim near Madison →Swim near Green Bay →Swim near Eau Claire →Swim near Wausau →Swim near La Crosse →Swim near Appleton →Swim near Oshkosh →Swim near Stevens Point →Swim near Rhinelander →Swim near Minocqua →Swim near Hayward →Swim near Eagle River →Swim near Wisconsin Dells →

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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More on swimming water quality

Best Lakes for Swimming in America, Ranked (2026)

The cleanest lakes for swimming, ranked on EPA nutrient and algae data — plus the one thing a reading cannot tell you the day you go.

Is It Safe to Swim in a Lake? E. coli and Advisories

What a swim advisory actually means, how E. coli monitoring works, how fast a lake clears after rain, and why a long-term reading is not a swim guide.

Lake Water Temperature by Month: How Warm Lakes Get

Typical lake surface temperatures month by month and state by state, from years of monitoring readings — when lakes warm up, how warm they get, and when they turn.

Best Month to Swim, by State — Typical Lake Temperatures

The month when the cleanest lakes in each state are typically warmest, from long-run Water Quality Portal readings rather than this year’s weather.

Source: EPA National Aquatic Resource Surveys, 2026.