Lady Gaga, Taylor Kinney, Vince Vaughn take charity polar plunge in Chicago

Lady Gaga and Taylor Kinney have taken the plunge -- no, not that kind of plunge.

The pop star, her "Chicago Fire" star fiance and actor Vince Vaughn were among those who jumped into the icy waters of Chicago's Lake Michigan at a fundraiser for the Special Olympics.

Special Olympics Chicago President Casey Hogan said Sunday that Gaga made the plunge with more than 4,500 other participants. Hogan says the singer's appearance was "a very nice surprise."

Lady Gaga -- who wowed viewers and Julie Andrews with her "The Sound of Music Tribute" at the Oscars -- announced her engagement to Kinney last month, sharing photos of the heart-shaped diamond ring he proposed with. Photos show her and a bare-chested Kinney going into the water together.

Vaughn also made the plunge. The native of the Chicago suburb Lake Forest was dressed in a Chicago Blackhawks jersey and jeans. The actor went in up to his knees, then eased himself down backward in the water.

Last year, comedian Jimmy Fallon jumped in wearing a suit and tie, and helped raise more than $1 million.

The air temperature was a frigid 20 degrees at the time of the plunge, according to the National Weather Service.