Visitors to parks are being asked not to drop rubbish after a mallard duck was spotted with a plastic bottle ring through its beak and round its head.
East Sussex Wildlife Rescue Service (Wras) said its officers had being trying unsuccessfully to catch the duck at Hampden Park Lake for two weeks.
"These cases are very frustrating," said rescue co-ordinator Trevor Weeks.
Wras said it also knew of two seagulls in the Newhaven area with plastic beer can rings around their heads.
Mr Weeks said: "This is a common problem and one which is so easily avoided.
"This is yet another example of how lazy humans can be and the problems we cause."
He added that the mallard duck was struggling to eat, but it would not be possible to catch him until he was weaker.