A member of Craigie-based Breakers Swim Club, Jack came first in the boys’ 14 years 5km open water swim at the Australian Open Water Championships in Queensland.
The previous day he finished fifth in the 10km event.
Coach Ralph McManis said a record 12 swimmers from the club qualified for the championships and most achieved personal best times.
“Many of our swimmers were experiencing their first national competition, having qualified here in Perth,” he said.
“Overall, Breakers swimmers performed exceptionally well and the future looks bright.”