Retired teacher Gordon Park was today found guilty of murdering his wife before dumping her body in Coniston Water.
Park, 60, had bludgeoned his wife Carol to death with an ice axe, the court heard.
He claimed she had vanished from the family home in Leece, near Barrow, Cumbria in July 1976 to live with another man.
The body of the mother of three, still wearing a blue baby-doll nightdress, was found 21 years later by amateur divers in August 1997.
A jury of seven women and five men found three-times-married Park guilty after a 10-week trial at Manchester Crown Court.
Park's son Jeremy sat with his arm around close family members as the verdict was read out.
The judge had asked everyone in court to behave "with dignity" as the verdict was read out.
None of his family made any sound as the jury returned the guilty verdict.
In the public gallery one man, thought to be a close relative of Carol Park, appeared to faint and fall from his seat.
The court was told Park brutally bludgeoned his "pretty and vivacious" wife Carol on July 17 1976 with an ice axe before wrapping her body in the baby-doll nightdress she was wearing.
He carefully trussed up her body in bags and dumped her body in Coniston Water in the Lake District.
The court was told Carol had enjoyed affairs with several men during the couple's nine-year marriage.
The remains of the mother of three lay undiscovered for 21 years before being found by chance by amateur scuba-divers in 1997.
If the body had been dumped just a few feet further from the shore, she would never have been found, the court heard.
Park, of Leece, near Barrow-in-Furness, reported his wife missing only after six weeks.
The court heard that following her affairs, the couple had enjoyed a series of rows and reconciliations.Reuse content