The closest station to the Aquatic Centre is the Olympic Park Station. Plenty of extra trains major event buses will run throughout the Competition because of the Royal Easter Show so the best way to get there and home again is by public transport.
Opal Cards are a cheaper way to take public transport in Sydney. They are widely available at convenience stores and at the airport.
Trip Planner can help you plan the route and cost.
Parking in Sydney Olympic Park will be in high demand during Nationals and carparks typically reach capacity early, particularly on weekends and public holidays. Attendees are strongly encouraged to leave the car at home and consider travelling by public transport instead to avoid delays.
If you choose to drive you may be able to arrange pre-booked parking. P2 is the closest parking lot.