The 54-year-old victim and his 16-year-old son were spotted by professional fisherman Reto Leuch on Saturday afternoon, he told newspaper 20 Minuten on Wednesday.
“I was getting out my nets when I saw someone signaling with their hands,” he said.
While the son was lying on the capsized boat, the father only had his upper body on the vessel, leaving his legs dangling in the water, which hovered around seven degrees, said the paper.
Leuch immediately pulled the boy on to his own boat. However the father was too heavy, so he called police to help him.
Both the victims were taken to hospital with hypothermia, however the 16-year-old has already been discharged, said the paper on Wednesday.
Speaking to the paper, the 54-year-old father said he was “doing better”.
Bordering Switzerland, Austria and Germany, Lake Constance, or the Bodensee, is 64 kilometres long, making it the third largest lake in central Europe.