The search began on Sunday afternoon after receiving a distress call from two people out on Georgian Bay.
One was found by emergency crews and was taken to hospital with non-life threatening injuries.
Joint Rescue Coordination Centre (JRCC) Trenton, West Region OPP Emergency Response Team (ERT), and the OPP Underwater Search and Recovery Unit (USRU) are assisting with the search.
Police are asking the public to avoid the area at this time.