"We went down like normal to check the pool out because Tuesdays and Thursdays the local ladies of Howard Springs do their water aerobics," park manager Geoff Thompson was quoted as saying on the Australian Broadcasting Corp.'s website.
A government ranger was summoned to remove the visitor, which was identified as a freshwater crocodile -- generally considered to be capable of giving a nasty bite but rarely fatal to humans.
"They were all there waiting for the ranger to collect it and once he got it out of the water they started their aerobics," Thompson said.
The crocodile was likely to be handed to a local wildlife park.
Crocodile numbers have burgeoned in northern Australia since hunting that pushed the animal almost to extinction was banned in 1971. Attacks on humans have increased, with four people killed by crocodiles in seven months from 2008 to early 2009.