The "Super Plunge" involves individuals jumping into Lake Michigan once an hour for 24 hours straight.
RELATED: Hundreds brave freezing Lake Michigan for 19th annual Polar Plunge
Those participating get to hang out in a heated tent near the Northwestern University campus between plunges, though.
People started the fundraiser Friday, and it's still going on Saturday in Evanston. The effort raises money for Special Olympics Illinois.
The 19th annual Polar Plunge at North Avenue Beach, hosted by the Chicago Polar Bear Club, raised money to help local families challenged by difficult circumstances. It took place on Jan. 25, and hundreds participated.