The man was taken by ambulance to hospital where he is being cared for.
The condition is critical, states Region Östergötland.
The alarm came just before 15.30 on Saturday after several witnesses saw a person fall off a boat.
The rescue service Östra Götaland launched an intensive effort in collaboration with the Sea Rescue Center and the rescue service in Valdemarsvik and Gryt.
- We have both helicopter and boat on site.
Our divers have now been working for 40 minutes, said Mikael Kalered, internal commander of the rescue service Östra Götaland, at 5 p.m.
The man was found at 5.20 pm, according to the rescue service.