Vandalism at a popular waterfowl park in County Down forced the facility to close after home heating oil spilled into its ponds from a nearby tank.
A volunteer discovered the spill on a Thursday morning when arriving to feed the animals, noticing a kerosene smell and finding the park's black swans completely covered in oil.
More than 20 birds were transported to the USPCA's headquarters last week for urgent specialist care, though the death toll has continued to rise.
Hayward said that she hopes the incident will serve as a deterrent to those engaged in vandalism.
"One of our volunteers appeared on the Thursday morning to feed, and walked down through the park and smelt this kerosene smell and saw the black swans completely oiled.""The incident was quickly confirmed as having had a significant impact on the ponds and NIEA inspectors deployed oil absorbent booms and other countermeasures as mitigation,"a spokesperson said.
The agency said the substance involved had been identified as home heating oil, or kerosene, and that the source had been traced to a nearby tank.
Hayward hopes that the incident will be an deterrent to those engaged in vandalism.