A man had been operating a boat Saturday on the lake approximately 40 kilometres southeast of the community when he ended up in the water and in distress.
Outlook RCMP said a woman on the boat tried to rescue him. She was not injured.
Saskatchewan Environment and Resource Management and Outlook Fire and Rescue are assisting with the search.
The RCMP Underwater Recovery Team is also involved with the search.
Police are asking everyone to stay away from the search area to allow emergency personnel to carry out their search.
No other details have been released.
Outlook is approximately 75 kilometres south of Saskatoon.