When driver Cameron Blaseotto heard a scratching sound coming from the engine compartment of his ute on Wednesday night, he was nervous to investigate what was inside.
Convincing a mate to open the bonnet, the pair were stunned to find a platypus sitting above the front wheel.
The stowaway had managed to become stuck inside after Mr Blaseotto and a friend drove across waters of the Murrumbidgee River at Angle Crossing about 8.30pm.
Despite travelling more than 15km from its natural habitat, the female platypus was deemed in perfect health and released back into the wild on Thursday morning.
"It sort of sounded like a possum or something under the car but we didn't hear it again so we went back down to Chisholm on the Monaro Highway.
"As we got home we heard the noise again so decided to have a look," the 18-year-old said.
"We both jumped back when we saw the platypus sitting there. I couldn't believe it and when we called the rangers, they all thought we were joking."
Mr Blaseotto, a disability support worker and volunteer firefighter, said that rangers came to the house to rescue the platypus within an hour of its discovery.
"If she's still alive and kicking it's pretty good, I think. It's the only way I could get a girl to come back to my house."
After spending the night with wildlife officers at the Namadgi Visitor Centre, the lucky animal was allowed to swim free back at Angle Crossing just after 9am.
ACT Parks and Conservation Service regional manager Brett McNamara said the events were unique.
"It's an extraordinary animal and an extraordinary tale," he said.
"I am sure when the platypus gets home tonight with her little mates, she will have an amazing story to tell."
Mr McNamara said rangers have recently launched a campaign about the danger of traps for the threatened species and Mr Blaseotto was to be congratulated for his actions.
"What's happened here, is Cameron has discovered the animal and called Canberra Connect and the Urban Wildlife program have responded.
"Their volunteers work 24 hours, seven days a week to help with urban wildlife around the ACT.
"I must admit the ranger thought twice at the report of a platypus in an engine bay."
He said the events proved the animal was a resilient species which should be respected in the wild.
"There are so many different elements to it, like the fact that she got into the engine bay in the first place and managed to hang on all the way into town with moving parts of the engine close by," Mr McNamara said.
"It's one of those amazing wildlife stories."
At last sighting, the platypus was swimming into the currents of the Murrumbidgee River.