Inside each of the unassuming containers is a cargo that could be the key to saving Australia's endangered Northern Corroboree frog.

The May field trip saw over 1000 eggs released into the wild. For Ms Loneragan, it was the pay off for the hard work leading Tidbinbilla Nature Reserve's corroboree frog breeding program.

Corroboree frogs were once in their thousands in the alpine Namadgi wetlands, with scientists describing "a moving carpet" of the tiny two-centimetre critters.

ACT park rangers estimate there were now fewer than 100 adult corroboree frogs in the wild in Canberra's alpine regions.

"Everything about the corroboree frog happens slower which is also a problem," Ms Loneragan said.

"You can imagine the cane toad: the female will lay about 20,000 eggs. These guys, a female will lay about 25 to 30 eggs."

"These guys take four years to reach maturity."

The 2003 bushfires burned through a lot of corroboree frog habitat, but the main problem the frogs have faced is a global frog-killing pandemic: chytrid fungus.

By releasing the eggs into the wild, rangers hoped the frogs would grow to develop a resistance to the fungus.

Tidbinbilla's corroboree frogs are housed in giant shipping containers, where they're overseen from egg to tadpole to adult.

Yet even then, there's little known about the frogs in the wild, even how long they lived. Some of the breeding frogs in the shipping containers had been with the program since it started in 2003.

"It's pretty amazing that they're still breeding, still laying their eggs and still doing their thing," Ms Loneragan said.

She and her colleagues arrived in the Namadgi mountains in a small convoy of utes, each carrying a bag of the containers down into the wetlands.

But before visiting the wetlands, rangers each dipped their shoes into a bleach solution to avoid the risk of carrying chytrid fungus into the habitat.

The moss lining the containers the rangers carried in was the same moss that lines the pools and creeks across the Namadgi wetlands.

Rangers delicately used the plastic spoons to place the eggs into the pools, under the moss or under the snow.

Fauna ecologist Claire Wimpenny said the eggs came from not just Tidbinbilla's breeding program, but the breeding program at Healesville Sanctuary in Victoria.

"I always hear these amazing stories how there were hundreds of calling males and you could find corroboree frogs everywhere [in the Namadgi]," Ms Wimpenny said.

"I guess this program gives me hope that we could possibly get back there one day."

Besides the container populations, Tidbinbilla staff are also breeding a population in outdoor ring tanks in the park.

Senior wildlife officer Jennifer Pierson said they had been concerned when they released a population of adult frogs from the shipping containers into the tanks last year.

"The first questions were: will we ever see them again," Dr Pierson said.

Ms Loneragan said 32 of the 33 frogs they had released survived.

Dr Pierson said they hoped to teach the frogs to adapt to the wild and they had thrived with very little input from staff. The frogs were even breeding and growing bigger than their mates in the containers.

"They just look burly," Dr Pierson said.

"The natural cues in the environment were just the cues they needed."