Reporting the news, 20 Minutes said injuries found on the body suggested it had been attacked by another animal, possibly a fox.
A non-native species usually found in Australia, the black swan's appearance on the lake near Vevey over the past few months was of concern to the Vaud cantonal authorities as they had no idea where it came from or who it belonged to.
At the end of May the authorities captured the swan to check it for diseases it could potentially pass on to native swans.
After a period of quarantine, they planned to give the bird to a zoo or animal park rather than release it back into the wild, complying with Swiss law which forbids the reintroduction of a non-native animal into the wild in Switzerland.
But the decision caused uproar among the general public, with many expressing their disapproval on a specially created Facebook group.
“We have been deeply moved by its brutal and incomprehensible capture....We don't understand the need to quarantine it and then put it in a zoo,” said the group's founder.
The authorities then changed their mind and the bird was finally released back into Lake Geneva amid great fanfare by Vaud environment minister Jacqueline de Quattro.
At the time de Quattro named the swan Nelson in homage to Nelson Mandela, "who fought for his freedom”.
She was then forced to defend her actions after BirdLife Suisse questioned the decision to release the bird, suggesting it was based on electioneering and was a “bad example”.