A teenager found the 50-centimetre juvenile freshwater crocodile lurking behind a garbage bin in a backyard in yesterday evening.

The girl told her mother and she rang wildlife rescue organisation WIRES.

"She went to move her garbage bin and found him behind it," Joanne Wenban, WIRES' rescue van driver, said.

By the time Rose the rescuer arrived at the house, she found the crocodile in an esky.

The crocodile - which has since been nicknamed Chainsaw - was handed over to NSW National Parks staff and was then taken to the Australian Reptile Park.

Chainsaw, believed to be two years old, was "very dehydrated", but otherwise in a reasonable condition, Ms Wenban said.

"He wouldn't have travelled that far given his small size. It would have been somewhere reasonably locally that he would have escaped from."

Liz Vella, a senior curator at the Australian Reptile Park, said Chainsaw might have been someone's illegal pet.

"In Australia, there is a certain amount of illegal trading in reptiles. There is a small chance they [the owner] could have got it from Northern Australia.

"But they could have bought it from someone."

Ms Vella said Chainsaw was receiving lots of "TLC" - including a tub of water to swim in and a heated light - at the reptile park to relieve him of the stress of being out of his environment.

He would be fed small pieces of meat such as crickets, cockroaches, mice and fish.

It is not yet clear where Chainsaw is set to go next. Ms Vella said he would not be released into the wild but kept in a zoo or at the reptile park.

"We don't know how long he has been cared for ... so we just want to get him into a nice pattern and assess his condition."

In 2006, a three-year-old male saltwater crocodile was captured after making a Dee Why pond its home.