Saskatoon RCMP responded around 8:45 p.m. and search efforts began immediately with Dundurn Fire and Rescue, STARS air ambulance, Saskatoon Police Service Air Support and the Saskatoon Fire Department.
Police say initial recovery efforts were unsuccessful due to darkness and strong winds.
The Manitoba RCMP Underwater Recovery Team is now assisting in the search efforts. Saskatoon RCMP will remain on scene at the far north end of the lake until recovery efforts are complete.
For the remainder of the search, police are restricting boat traffic at the north end of Blackstrap Lake.
People are being asked to use alternate boat launches to give resources enough space to conduct the search.
The man was the lone occupant of the jet ski, according to police.
Blackstrap Lake is located 35 minutes south of Saskatoon.