The man was found floating in the water on Friday morning, and attempts to resuscitate him were unsuccessful.
A police spokesman told local newspaper Namdalsavisa that an inquiry had been opened into the death.
He said that no witnesses to the death has been found, and the body has been sent to Trondheim for autopsy.
Marine Harvest communications manager Ola Helge Hjetland confirmed to Namdalsavisa that one of the company’s staff died at work.
“This is a tragic event, and our thoughts go to relatives and his closest colleagues. We ask for understanding that we cannot comment on this further now,” he said.