The Lake Forest Fire Department responded around 2:44 p.m. to the Lake Forest Boat Launch for a call of a missing boater, fire officials said.
The missing boater, who was on a 15-foot sailboat, was reported missing by a family member to Lake Forest police after they failed to meet them at the boat launch Sunday afternoon.
The person's age, gender and identity were not immediately released by authorities.
Emergency crews launched a search for the missing boater, but the water search was halted for the evening around 5:30 p.m., fire officials said.
"The water conditions were challenging, with waves reaching 4 to 6 feet," a statement from fire officials read in part. "In response, Lake Forest command called the U.S. Coast Guard for additional support.
A Coast Guard helicopter has been assisting with the search.
No further information was immediately available.