Mendota Freeze Contest

media release: After a stretch of cooler weather, temperatures are turning milder again, but winter is still on the way. That means it’s time to guess when Lake Mendota will ice over. The 2025–26 edition of the Mendota Freeze Contest, hosted by Clean Lakes Alliance, officially opens Saturday, November 15.

According to more than 170 years of continuous freeze data from the Wisconsin State Climatology Office, the median freeze date for Lake Mendota is December 20. Past years show wide variation: the earliest recorded ice-on date is November 23, 1880, and the latest is January 30, 1932.

“When the lakes freeze, they become our largest parks,” said Executive Director James Tye. “While many think of the Yahara lakes only in summer, they’re the center of our community year-round—winter included.”

Last winter, Lake Mendota officially froze on December 25, 2024. Just two days later, the ice opened on December 27, as temperatures climbed into the 40s. The lake refroze on January 7, 2025, and remained iced over until March 15, 2025. That freeze duration of 69 days of ice cover was well under the long-term median freeze duration of close to 100 days.

Mendota Freeze Contest Details

The contest opens Saturday, November 15, 2025, at 7:00 a.m. and runs until Monday, December 15, 2025, at 11:59 p.m.

Participants are asked to guess the official ice-on date for Lake Mendota (as determined by the Wisconsin State Climatology Office).

All correct guesses will be entered into a random drawing for local gift cards.

Only one entry per person/email address is permitted; multiple entries will be disqualified.

Visit mendotafreeze.org for complete rules, entry form, and historical freeze data.

Record Freeze Duration

Lake Mendota holds a record of 161 days of ice cover during the winter of 1880-81. The lake froze on November 23 and didn’t thaw until May 3. Wisconsin Alumni Association

Freezing Later Than It Used To

Analyses show that the lake is typically freezing about 15 days later than it did decades ago. Nelson Institute

Why It Matters

Monitoring when Lake Mendota freezes provides not just a fun winter community activity,it also offers insight into how our local climate and lake ecosystems are changing. The number of ice-cover days is one of the many indicators scientists use to track how warming temperatures affect our lakes. This year’s contest is an excellent way for individuals of all ages to engage with the lakes, learn about our watershed, and become active stakeholders in protecting them.

“The lakes don’t just support summer recreation,” Tye added. “They play key roles in our local environment, culture, and economy through every season.”

Clean Lakes Alliance is a nonprofit organization dedicated to the improvement and protection of the lakes, streams, and wetlands in the Yahara Watershed. Through community support, advocacy, and education, we work to restore and protect our lakes for future generations.

cleanlakesalliance.org