The retiree, a resident of the canton of Bern, received a suspended one-year jail term from the regional court, Le Matin reported online.
He was found guilty of killing the woman, from the canton of Aargau, whose legs were injured so badly by the propeller of the boat that she bled to death, according to court evidence.
The victim had been in the canoe with her fiancee, who survived the crash on July 11th 2010 without serious injuries.
The couple were set to marry three weeks later.
The motor boat sped off without stopping.
The convicted man denied the charges against him but refused to testify in the case.
During the investigation, the operator of the motor boat and his two passengers declared that they were unaware of anything abnormal on the day of the accident, ATS reported.
The verdict of Judge Elizabeth Ochsner was based on the testimony of witnesses and the DNA analysis of human remains on the boat’s propeller, Le Matin said.
The victim’s companion and other observers identified the 77-year-old’s boat.
The convicted man, meanwhile, presented investigators with two conflicting versions of his boating activities on the lake on the day of the accident.
The court found the man was operating the boat carelessly and also noted that his vision was impaired by a cataract.