When will Mendota freeze?
Every winter since 1855, someone has watched Madison's lakes and written down the day the ice closed and the day it let go. Here are 170 winters of that record, what it says about this one, and where to plunge in the meantime.
170 winters, freeze to thaw.
Each thin bar is one winter, running from the day the lake froze over to the day it opened. The lines trace the 20-year median of each date. Hover any winter for the details.
Show the data as a table
| Winter | Froze | Thawed | Days of ice |
|---|
Will it be frozen by…?
Pick a date. We'll tell you how often Mendota has been frozen over by then, across the whole record and in this century alone. (The UW Center for Limnology runs a friendly ice-on pool every year. This is your edge.)
"Frozen over" is the official ice-on call by the State Climatology Office. Brief early freezes that broke up again count as frozen on the day they first closed.
The ice season is getting shorter.
Mendota has lost roughly three weeks of ice per century, and freezes about two weeks later than it did in the 1800s. Monona, shallower and quicker to freeze, shows the same trend.
| 1856–1900 | 1901–1950 | 1951–2000 | 2001–2026 | |
|---|---|---|---|---|
| Mendota · avg days of ice | 114 | 102 | 99 | 82 |
| Mendota · median freeze | Dec 17 | Dec 20 | Dec 22 | Jan 1 |
| Monona · avg days of ice | 117 | 105 | 95 | 88 |
| Monona · median freeze | Dec 11 | Dec 14 | Dec 18 | Dec 19 |
Badger Sauna calculations from Wisconsin State Climatology Office records. Winters with incomplete records are excluded from averages.
The extremes, on the books.
Mendota closed before Thanksgiving, and stayed closed for 161 days.
The latest Mendota has ever frozen. Second-latest: Jan 20, 2007.
1880–81 on Mendota, and 160 on Monona the same winter.
2001–02 on Mendota. For Monona, 44 days in 2023–24.
2025–26 on Mendota: 71 days. Monona froze Dec 12 and held 89.
Mendota froze on Christmas, opened two days later, then refroze Jan 7.
Where Madison goes in.
You don't need ice to plunge. Here's where people get into Madison's lakes, plus the places that put a hot sauna right beside cold water.
Sauna + plunge, done for you
Madison Saunas
Two wood-fired cedar saunas at Wingra Park, with a plunge straight into the lake. Opens November 6, 2026. From $27.
In our sauna guide Sugar River · PaoliTuli Sauna & Plunge
A glass-walled wood-fired sauna on a trout stream, open year-round, about 25 minutes from downtown. $39 for 80 minutes.
In our sauna guide Indoors · 54°FSaunaday
No lake, but a four-foot-deep tiled plunge pool kept at 54°F, a block from Lake Monona. $55 for two hours.
In our sauna guidePublic shoreline people plunge from
James Madison Park
614 E Gorham St. The downtown beach, with a shelter and restrooms in season. Park hours 4am–10pm.
Tenney Park
1330 Sherman Ave. A beach with a paved path. Stay off the lagoon ice, which officials warn can be thin and over five feet deep.
Warner & Spring Harbor
Warner Park (1101 Woodward Dr) on the north side, and Spring Harbor Beach (1918 Norman Way) on the west.
B.B. Clarke Beach
835 Spaight St, Willy Street's beach. A woman fell through thin ice off the 800 block of Spaight in January 2025, so stay in open water near shore.
Olin Park
1156 Olin-Turville Ct. For years the home of Madison's Polar Plunge, with big parking and skyline views.
Olbrich Park
3527 Atwood Ave. Ninety acres on the east shore, with a boat ramp, parking and the Biergarten for afterward.
Vilas Park
1501 Vilas Park Dr. The 2026 Polar Plunge site. Madison Saunas is just around the shore at Wingra Park.
The Foxie Dippers
A women's cold-water group that has met Sundays at 11am in the Yahara since 2023. Find them on Facebook.
County & state parks
Goodland County Park on Waubesa, Lake Kegonsa State Park (open 6am–11pm year-round) and Governor Nelson State Park on Mendota's north shore. A state park sticker is likely needed.
There are no lifeguards at any Madison beach, even in summer. Public Health Madison & Dane County only tests water quality from Memorial Day to Labor Day, so in plunge season, judge the water by eye: skip anything that looks like pea soup or paint, and avoid plunging after heavy rain.
Lake Mendota, month by month.
Average surface temperature from the UW–Madison buoy, 2021–2025. Under the ice, the water sits just above freezing at the top and about 39°F below.
Source: UW–Madison Space Science & Engineering Center and Center for Limnology buoy data, our averages. The buoy is pulled for winter. See today's reading on Mendota Live.
Cold water is serious water.
Madison firefighters pulled 39 people from the lakes after ice failures between 2016 and 2025. Most plunges are joyful. These rules keep them that way.
Never alone
Bring a friend who stays dry and on shore, with a phone, a rope and a warm layer.
Breathe through the gasp
Cold shock hits in the first minute. Walk in slowly, exhale long, and never jump or put your head under on entry.
Shorter than you think
There's no safe rule like "a minute per degree." Below about 41°F, ten or twenty strokes is plenty. Build up over weeks.
Watch for afterdrop
You're coldest about ten minutes after you get out. Dry off, layer up, have a warm drink, and don't drive until you've rewarmed.
No ice is safe ice
The Wisconsin DNR doesn't monitor ice. Avoid inlets, outlets and springs: the Yahara mouths, the Tenney and Vilas lagoons. Commonly cited guidance is 4"+ of clear ice just to walk.
Hearts first
The hot-to-cold switch strains the heart. If you have heart disease, talk to your doctor before plunging after a sauna.
You'll hear the "1-10-1" rule: 1 minute to control your breathing, 10 minutes of useful movement, 1 hour to unconsciousness. It's a useful memory aid, but the National Center for Cold Water Safety calls it oversimplified. Incapacitation can come much faster in very cold water.
Pair your plunge with the season.
Special Olympics Wisconsin's Madison plunge. In 2026 it moved to Vilas Park and Lake Wingra over two days, with 800+ plungers.
Clean Lakes Alliance's free festival on the Mendota ice at The Edgewater, with kites, a 5K and the whole city on the lake.
The Four Lakes Ice Yacht Club, founded 1921, is one of the largest in the world. Watch them fly on Mendota and Monona.
Clean Lakes Alliance runs a public Mendota freeze contest. Use the odds above to make your guess.
City rinks and lagoons at Tenney, Vilas and Elver, with warming houses and rentals when conditions allow.
Mendota is frozen when you can no longer row a boat between Picnic Point and Maple Bluff. That's a tradition from the lake's first limnologists.
Lake ice FAQ.
When does Lake Mendota usually freeze?
Across the full record since 1855, the median freeze date is around December 20–21. Since 2001 it has shifted to about January 1, and Mendota has frozen in December in only 12 of the last 26 winters.
Who decides when the lake is frozen?
The Wisconsin State Climatology Office makes the official ice-on and ice-off calls for Mendota and Monona, continuing observations that go back to the 1850s. Ice-on means the lake is essentially covered and stays that way. A skim of ice that blows open doesn't count.
When does the ice go out?
Mendota's median ice-out date over the full record is in early April (around April 3–4). In recent winters it has usually opened in March: March 13 in 2026 and March 15 in 2025.
Why does Monona freeze before Mendota?
Monona is smaller and shallower, so it loses its summer heat faster. Since 2001, its median freeze date (Dec 19) runs nearly two weeks ahead of Mendota's (Jan 1).
Is it safe to walk on the ice once it's declared frozen?
No. Ice-on is a statement about coverage, not thickness. Ice thickness varies a lot, especially near inlets, outlets, springs and the Yahara River. Check current conditions and local guidance, and never go out alone.
Data retrieved October 5, 2026
Freeze and thaw dates are from the Wisconsin State Climatology Office (Monona record). Averages, medians and trends are Badger Sauna's calculations. When a winter froze and opened more than once, we use the first freeze, the final thaw and the total days of ice. The full dataset is available as JSON. Reporters and teachers are welcome to use it with credit to the State Climatology Office.