The mid-afternoon attack at Tysslingen lake in central Sweden Sunday disrupted a peaceful scene for the birds and bird-watchers,The Local reported.
"Suddenly we heard the explosions and the swans become very upset. Then we saw rockets coming toward the swans, which went into a panic and began trampling one another. And several got stuck in a chain-link fence," said John Hall, a freelance photographer.
It was "total chaos," said another onlooker.
"Every bird disappeared and there was nothing left to see," said Helny Olsson. "It [was] so gruesome, so deplorable. It was either a stupid prank, or it could be so bad that there are some who got annoyed by the birds and their song."
The birds eventually returned to Tysslingen.