Some welcomed the rules, saying it was inappropriate for children to be lining up for rides behind people with almost-bare bottoms.
"I'm all for showing off a great body! But I was rather put off taking my children back when there were female butts everywhere!" one mother, Pauline Arnold, wrote.
"Couldn't be more proud of a company for taking such a stand. During a visit to the park recently, with three young teens, I couldn't believe the amount of 'cheek' I had to unwillingly view! Didn't know where to look most of the time! It was disgusting," Sharon Zuidema added.
But others called the dress code ridiculous, labelling it "sexist" and a form of "body-shaming".
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"This is so disgraceful! The first bikini in the diagram is the standard cut," Laura Powers wrote.
"This goes for men's Speedo's as well right? Cos don't wanna see that," Melissa-Rose Blake said.
Adventure World said in a statement that its dress standards were in line with other water parks around Australia, and as a family-friendly venue, it felt the rules were appropriate.
"Let's not confuse the issue. This update is about dress standards and dress standards only. It is not gender specific," it said.
"Adventure World is a family friendly theme park. We keep informed of industry trends and whilst this was not a decision taken lightly, it is in line with other parks nationwide.
"We are not the first park in Australia to update their dress standards on this subject, nor are we the only venue in WA that has addressed the matter with a similar policy."
The park's official conditions of entry state that visitors are welcome to wear whatever swimwear they feel comfortable in, "providing it is suitable for a family environment".
Wet'n'Wild and Dreamworld, two other water parks on the Gold Coast in Queensland, also prohibit provocative bathers.
"To ensure a safe and enjoyable family environment, provocative, G-string swimwear or underwear as swimming attire is not allowed," Dreamworld's conditions of entry state.
"If your clothing or swimwear does not comply with these regulations, appropriate attire is available for purchase at Beyond the Beach Gift Shop."
