Inside the swim across Port Phillip Bay's most challenging waterway

For Priscilla Chow the water is where she usually takes her troubles, but today it's the ocean making her nervous.

"Today's aim is to get through it," she explains of the nearly 4-kilometre ocean swim ahead, which will take her across one of the most treacherous stretches of water in Australia.

While the distance might not be daunting for endurance swimmers — the location is.