The accident occurred near an island in Fisksjön lake between Hammarstrand and Kälarne in Jämtland County.
The 65-year-old woman and her 72-year-old husband were out on their rowboat when a sudden gust of wind caused the boat to capsize, he local Länstidningen newspaper of Östersund reported.
While the woman was able to swim back to shore of the island where the couple had a summer cabin, her husband drowned and later washed up on shore.
After the accident, the woman attempted to call emergency services on her mobile phone, but the phone didn't work and her calls for help weren't heard on the mainland.
The 65-year-old old woman found herself marooned with her dead husband, unable to eat or sleep for three days.
"She was in shock the whole time," her son told the Expressen newspaper.
But on Saturday, the woman heard voices on the mainland and began banging and calling for help.
This time, her cries were heard and she was rescued.
Police received reports around noon on Saturday that a 72-year-old man had drowned in a boating accident, only learning later that the accident had occured three days earlier.
"There were some kids who heard her and their father went out and saw the body," Magnus Sundström, an emergency services worker who led the operation, told Expressen.
While police have launched an investigation into the incident in accordance with standard procedures, there are no suspicions that a crime was committed, according to Sveriges Radio (SR).