The male and female white swans were taken in by the charity Swan Lifeline after swallowing diesel when it leaked into North Lake at South Hill Park in Birch Hill last month.
Wendy Hermon, treatment centre and rescue co-ordinator for the charity, said: "They are absolutely fine now. I think everyone is so happy they are back. We've had a few calls from people saying how glad they are."
She added: "It would be really good if people can keep an eye on them and ring us if there are any problems - I'm sure people will contact us because the swans are very well looked-after there."