They were called out to an area near Tecumseh about 5:45 Saturday Afternoon.
Several people in a boat about half a kilometer off shore decided to go swimming.
One of the people did not return to the boat.
A search and rescue operation was conducted last evening and the OPP’s Underwater Search and Recovery Unit (USRU) will attend today to continue what has now been deemed a recovery operation.
Further information will be provided as it becomes available.