Mrs Watson, 55, who lives in south-west England, has a rare type of muscular dystrophy called central core disease.
She stopped swimming due to the lower pool temperatures.
“I used to come out and I couldn’t get warm,” she said.
Central core disease is a genetic condition affecting the muscles, usually leading to weakness in the muscles closest to the centre of the body, such as hips and shoulders.
Swimming is a non-weight-bearing exercise, making it ideal for Mrs Watson. For 10 years, she swam five times a week.
She said: “I can walk in a pool like a normal person. I feel normal in a pool. I look like every other swimmer in there.”