The man is said to have been found lifeless at a bathing place in Kvicksund.
He was taken out of the water and a person on the scene began cardiopulmonary resuscitation.
The man was later taken to Nya Karolinska Hospital in Solna by ambulance helicopter, but later died.
Relatives are notified.
The police do not suspect any crime.
On Saturday, the rescue service was also alerted to a drowning accident in Katrineholm municipality.
A woman was taken to hospital, but later died.