CHICAGO (WLS) — A swimmer has died after being pulled from Lake Michigan at 31st Street Beach, officials said.

The Chicago fire and police departments mounted a concerted effort to locate the missing swimmer on Monday afternoon.

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ABC7 saw crews pull out an unresponsive man who had been under water for about an hour.

CFD divers had been searching close to the shore at 31st Street Beach, and ABC7 counted at least four search boats and a helicopter that were deployed to the scene.

Witness Jose Vazquez runs a charter boat business near the beach. He told ABC7 that a group of about a dozen or so young people were hanging out at the pier when a member of that group apparently jumped into the lake around 2 p.m.

The man was about 50 feet from the pier when he began struggling.

“I was on my bike. I came up here, and I noticed there was a guy backstroking, jumped off the pier. He was backstroking, and then he just went down,” Vazquez said. “Really, because the current is really strong. The water is really cold. Probably shocked the body.”

The water temperature is in the high 40s, creating challenging conditions for even the strongest of swimmers.

“When you’re jumping into water like this with this strong current and this cold weather, a lot can happen,” Vazquez said. “Too cold, too windy, too early to get in that water.”

Crews pulled the unresponsive man from the water after about an hour-long search effort. They performed CPR on him before rushing him to the University of Chicago Medical Center in critical condition.

The Cook County Medical Examiner’s Office later confirmed that the man died. His identity has not yet been released.

As a reminder, the beaches do not officially open in Chicago until the Friday before Memorial Day, so there were no lifeguards on duty on Monday, and swimming is prohibited until opening day.

Further information was not immediately available.