The event has grown tremendously over the last 20 years, making it one of the largest "plunges" in the country.
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The plunge benefits the Special Children's Charities and the Special Olympics Chicago programs. It also serves more than 7,500 athletes throughout the city.
The Chicago Polar Plunge started at North Avenue Beach in 2000, where 50 participants raised $20,000.
The event attracts more than 4,500 plungers and is on track to raise more than $2 million.
The first "plungers" dove in around 10:00 a.m. at North Avenue Beach located at 1603 N. Lakeshore Drive.
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The proceeds from the event will help fund activities, events, transportation and more for athletes throughout the city.
Registration is still open and can be completed online or in-person at North Avenue Beach starting at 8:00 a.m.
For more information visit: www.chicagopolarplunge.org.