Kathryn Mason is an Australian-born UK open water marathon butterfly swimmer. She holds the all-Ireland record for distance butterfly set in Lough Erne, Northern Ireland in 2012 at 25 km. She swims without a wetsuit and without hydration or food, non-stop where possible. She is a self-trained and self-funded competitor who fits in a training schedule around work hours. She also swims freestyle open water at the amateur level.