Wendy Hermon, from Eton-based charity Swan Lifeline, became concerned after two swans were found in Windsor with wounds believed to have been caused by airgun pellets.
Mrs Hermon, treatment centre and rescue co-ordinator at the charity at Cuckoo Weir Island, South Meadow Lane, said: "We have had quite a few of these incidents over the last year. I don't know whether people are doing it for fun or for food, but it just seems to be getting worse.
"I'm really worried that the people who have done this will come back and do it again."
On Wednesday last week, a male swan was found dead floating in backwaters around Cuckoo Weir Island at around 4pm. Later that day, at 6.15pm, a member of the public spotted its female mate with a wounded cheek in the river at Barry Avenue, Windsor.
Swan Lifeline will care for the injured swan before releasing her back into the wild and Mrs Hermon said she is 'recovering well'.
The charity also cared for three swans which were shot in Windsor in May. The shots were believed to be fired from an airgun.
Thames Valley Police are investigating and a spokesman said: "We urge anyone with any information about the shooting of these two swans to come forward and get in contact with us to help with our enquiries."
Anyone with information about the incident should call police on non-emergency number 101 or Crimestoppers charity anonymously on 0800 555 111.