A man from Sydney's south has channelled the late Steve Irwin and captured a freshwater crocodile on a riverbank during an afternoon stroll.

Aaron Hughes was walking with his wife and their young son Ben along Salt Pan Creek, behind their Peakhurst home, yesterday when they spotted the out-of-place reptile sunning himself on the mud.

The croc measured about 80cm long.

"We had to take a double-take. We couldn't believe what we were seeing," Mr Hughes told ABC Radio today.

Aaron Hughes caught the crocodile yesterday afternoon. (9NEWS)

Mr Hughes said the croc didn't move "too quickly." (9NEWS)

"My wife and I looked at each other - we were having a bit of a laugh to be honest about what to do next."

He said it quickly dawned on them the animal was one of two juvenile freshwater crocodiles reported missing from a nearby wildlife park on March 3.

"It had been a bit of a running joke around the streets and with my friends that those crocs were going to be turning up in a few years being two metres or three metres long," Mr Hughes said.

"As we've all done, we've seen Steve Irwin and the Crocodile Hunter, we thought that we were well-versed in maybe coming up behind it and grabbing it as it wasn't really moving too quickly, so that's what we did.

The Hughes' notified the owners and kept the reptile in their bath until police arrived.

The baby croc is one of two missing from a mobile Sydney wildlife show. (9NEWS)

The reptile measures 80cm long. (9NEWS)

Keepers from Get Wild Animal Experiences - a mobile Sydney wildlife show - had been scouring Georges River since the reptiles' disappearance more than six weeks ago after a report of a crocodile sighting in the water.

Grave concerns were held for the crocs, named Snap and Crackle, as temperatures across the state plummeted.

"We think we managed to get hold of Snap because he did have a few goes when we were bringing him up to put him in the bath, so there is one still out there," Mr Hughes said.

The wildlife business issued an update last night following the crocodile's return.

"He is very cold, thin and lethargic but we are hoping with some TLC he will be back to normal in no time," a statement on the Get Wild Facebook page read.

"We are beyond happy and would like to thank Aaron who contacted us and Kogarah Police for assisting in this matter."