One man is dead and a woman is missing after the duo and eight others encountered dangerous conditions during a swim in Lake Michigan on Sunday, officials said.

Rescuers are searching Lake Michigan near Highland Park, about 25 miles north of Chicago, Monday for the 52-year-old woman from Elgin, who has been missing since waves swept her away from the rest of the group at around 9:15 a.m. Sunday. Ten people from a cold weather swim group were swimming in the lake when they “encountered difficulty due to lake conditions,” the City of Highland Park said in a news release.

Emergency responders arrived at the lake and found two swimmers in distress. A man, 46, was pulled to the shore at Park Avenue Beach and taken to the hospital, where he later died.

The U.S. Coast Guard said the group was at the beach for a “polar-plunge type event,” The Chicago Sun-Times reported.

Steve Knapp, a member of the North Shore Yacht Club, told the Chicago Sun-Times he saw two men and a woman struggling in the water.

“I abandoned the two guys,” Knapp recalled. “The girl’s situation was more dire. She was still moving, but drowning.”

Knapp said he and other yacht club member tried to save the woman. He went to grab a pole with a hook, but came back and couldn’t find the woman in the water.

“I’m feeling pretty mad at myself for not jumping in,” Knapp said. “…I wasn’t a hero.”

Authorities did not identify the swimmers.

“Police departments along the Lake Michigan shoreline in Illinois and Wisconsin have been advised to monitor their beaches for the missing swimmer,” the city said.