"A bit too optimistic," she wrote on the video. "I was so sure I could cross."
It's likely the video was filmed near Byron Bay where Pataky and Hemsworth live in a sprawling $20 million compound.
The area was recently pummelled by two days of rain.
In the series of lighthearted videos that she uploaded, Pataky was shown saying, "Oh god, what am I doing?" before announcing, "My only option, through the window."
After climbing out of her car, Pataky waded out of the water and later received help from friends including Hemsworth's personal trainer Luke Zocchi who towed the car out of the troubled spot.
"What would I do without you guys," Pataky said to her rescuers.
Pataky and Hemsworth have been married for 10 years. The Thor star recently revealed the "complicated" reason why his wife didn't take his surname.
Hemsworth explained to Kyle and Jackie O that at one stage Pataky, 43, had been keen to adopt the Hemsworth surname – but passport issues kept her with her maiden name.
"I think that she actually wanted to do it. I think she still may," he said. "I think it was when we were coming back from America. We were living in Europe and deciding where to go. It was a complication of passports and so on."
Kyle joked: "That's what they all say – you know she's just waiting to see whether it works out or not."