Although she'd never, had any particular interest in birds, let alone touched one before, Dot was determined to help.
After enlisting the services of a local vet to free the dying swan, she used her nursing skills to tend him.
Keeping a watch over the swan and its seven cygnets over the next few months, Dot was horrified to discover they came under threat from anglers, pollution and vandals again and again.
In total there were 27 incidents in just four months.
And Dot realised exactly the same thing must be happening in lakes and streams around the country.
It was the start of a project which has already won the 53-year-old grandmother the British Empire Medal.
Horrified to discover the scale of the problem, Dot offered her services to the RSPCA and started taking in injured swans.
However, she soon decided she had to do even more. So, in 1988, Dot sold her house and gave up her job in an old people's home to start The Swan Sanctuary in Egham, Surrey on a three-acre plot leased from the council.
Claiming the only thing she missed was her lovely bathroom, Dot moved into a caravan while she and a team of volunteers dug ten ponds, four rehabilitation lakes, an operating theatre and an X-ray room.
Now Dot - who still lives in a caravan on site - is helped by her daughter, Melanie as well as volunteers.
On call 24 hours a day, Dot rarely manages to catch more than three hours' sleep a night.
As well as caring for 4,000 water birds such as swans and grebes every year, Dot has to raise over £90,000 a year to keep the sanctuary afloat.
"We do it on a wing and a prayer," she jokes. "The strange thing is I'm not some batty old woman who adores birds. I actually prefer cats. But I saw a need and I couldn't say no."
Dot now has five small centres around the country and is about to expand even further.
Later this year she is opening a 50 acre site nearby which will also house an education centre to encourage youngsters to learn how to value the environment. "The problem is greater than ever," says Dot.
"These birds are so precious and yet they face danger every day - from pylons, pollution, anglers and vandalism. If we allowed swans to be wiped out, how could we face the next generation?"