Crews are searching for a man who went missing in the Fox Lake in north suburban Antioch on Monday evening.
The Lake County Sheriff's Office said two men were in a boat, test-driving it, when they apparently turned too quickly and were thrown off of the boat.
A passing boat rescued one of the men, but the other went underwater, the sheriff's office said.
Crews are actively searching for him, the sheriff's office said in a statement at 7:45 p.m.
First responders are calling this a recovery mission.
Further information was not immediately available.
This is a developing story. Check back with ABC7 for updates.