Two snowmobiles have broken through the ice on Six Mile Lake near O'Leary's Island, police say.
A cottager observed two people in distress at about 10:45 a.m. and called 911 to report the incident.
Local residents quickly responded to help the snowmobilers.
They were soon joined by officers from the Southern Georgian Bay OPP detachment, OPP Aviation Services, Georgian Bay Fire Department in addition to Simcoe County and Muskoka Region paramedics.
One male was removed from the cold water and was transported to a local hospital.
The second party has not been located. However, rescue efforts are continuing, officials say.
No other information is available at this time.
The OPP warns people to exercise extreme caution near any bodies of water, stressing no ice is safe ice.