A species of frog has been found alive on a farm in Australia more than 30 years after it was thought to have become extinct. Environment officials have said a thriving population of yellow-spotted bell frogs has been found in a remote creek in New South Wales. 

The yellow-spotted bell frog is back from the dead.  It was thought to have become extinct but has now been seen for the first time since 1973.

Dr. David Hunter, a threatened species officer at the New South Wales Environment Department, was there when about 100 frogs were found in a remote stream, the location of which is being kept secret.

"This was definitely the most exciting moment of my career and I'd be surprised if I'll repeat it," he said.  "We really don't want anyone going to the site, trying to see the bell frog or capture the bell frog, because there's always the possibility that that could actually introduce an unknown pathogen into the population and cause a problem.'

The yellow-spotted bell frog's disappearance is likely to have been caused by a range of factors, including disease, a loss of habitat and pollution.

Experts believe that exposure to a deadly fungus that arrived in Australia from Africa in the 1970s decimated frog numbers.

A collection of tadpoles has been established at Taronga Zoo in Sydney as part of a plan to re-populate rivers and streams.

The zoo's Michael McFadden says the breeding program should help this vulnerable species survive. 

"We need to get an insurance population so that if something bad does happen over the next year and they are totally gone, we have at least not lost that species and we can work at re-introducing them back into their natural habitat," McFadden said.

Scientists have warned there are more than 40 threatened frog species fighting for survival in Australia.

The International Union for Conservation of Nature has said that one-third of the world's 6,000 species of amphibians are under threat of extinction.

The New South Wales Environment Minister, Frank Sartor, said the discovery of yellow-spotted bell frogs was the amphibian equivalent of discovering the Tasmanian Tiger, a carnivorous Australian marsupial that died out in the 1930s.