The 63-year-old star had to shoot a sequence which involved her running into the ocean with her clothes on at Garie Beach, south of Sydney.
Weaver admits she is not a strong swimmer and had to be pulled from the water by lifeguards twice as the waves knocked her off her feet and left her gasping for breath.
She tells Australia's Daily Telegraph, "It's a really beautiful beach but quite treacherous. There was a rampaging surf. In this particular scene I had to run into the water with my clothes on and I'm not a good swimmer.
"I had to do a few takes and each time it was so rough a lifeguard had to rescue me. I was really scared because I had swallowed a lot of water."
Weaver was filming a currently untitled short movie, directed by Alexandra Schepisi.