At 1553 hours, Co. 7 and Co. 79 were dispatched for a possible subject through the ice at Placid Harbor. Ambulance 796 responded immediately with four personnel. Broken ice was reported at the end of a pier. Earlier in the day the ice was observed solid and unbroken. It was unknown if a victim was in the water. Calvert Boat 3 responded. Using their sonar, the area around the dock was scanned. No victim was detected. Chief 7A placed all units in service at 1655.