An off-duty Chicago firefighter died while swimming in Lake Michigan early Sunday.

The firefighter was at the lakefront with his family after his work shift when he went under the water and did not resurface, the Chicago Fire Department said in a statement.

Divers searched for him and quickly found him underwater, fire officials said.

He was taken to the University of Chicago Medical Center, where he was pronounced dead.

“While this incident did occur off duty after his shift, we are conducting a full investigation to determine the status of this tragic loss,” Fire Commissioner Annette Nance-Holt said in a statement.

No other details were immediately available.