Biodiversity in Kakadu National Park has been "decimated" by cane toads in recent years, with some species disappearing from sight altogether, according to one of the NT's leading toad experts.

Key points: A parliamentary inquiry into combatting cane toads has heard anecdotal evidence about the damage toads are doing

A parliamentary inquiry into combatting cane toads has heard anecdotal evidence about the damage toads are doing Leading NT cane toad expert Graeme Sawyer says the Federal Government has had its "head in the sand"

Leading NT cane toad expert Graeme Sawyer says the Federal Government has had its "head in the sand" Parks Australia canned its cane toad management programs, branding them a "waste of time"

Graeme Sawyer from Biodiversity Watch levelled the blame for the toads' destruction of Kakadu on a Commonwealth Government that he said had "its head in the sand" in dealing with the issue.

Mr Sawyer last week told a parliamentary inquiry into controlling cane toads that the "devastation on the wildlife out [in Kakadu] is something you have to see to believe".

"When you look at country up here — like those places in Kakadu along the Jim Jim Creek in the areas where I've been doing my research, and just hanging out for the last 30 years around Mount Ringwood station — the impact of toads 15 to 20 years in is unbelievable," he told the Canberra inquiry.

The Commonwealth has "dropped the ball" completely on cane toad management in the Territory's Top End, he said.

Cane toads, a deadly pest first introduced to Australia to help eradicate sugar cane beetles in the 1930s, first reached Kakadu in the early 2000s.

They have continued to be an invasive, predatory scourge on ecosystems and carry poison which can kill the native species which attempt to eat them.

Pythons, goannas disappear from sight: Sawyer

Mr Sawyer told the ABC he had witnessed a plunge in the levels of biodiversity in Kakadu during recent trips to the world-heritage listed area.

Biodiversity Watch's Graeme Sawyer is calling on the federal government to do more on toad management. ( ABC TV )

"In eight or so trips into that country [around Jim Jim Creek] including lots of walking around at night, we never saw an olive python or a water python, we saw about two slatey grey snakes, and nothing else in the reptile species," he said.

"No goannas — none of the people who live there had seen a goanna for like seven years — when they used to eat them on a regular basis."

While data on how much damage the toads were doing to Kakadu remained inconclusive, Mr Sawyer said the signs of destruction were there.

"The collapse of those systems — and when you look at the numbers of toads and where they are, and you map that up with some of the biodiversity stuff, it's awful," he said.

Thousands of toads along creek system

There were populations of "thousands" of toads along the Jim Jim Creek system, in a two-and-a-half-kilometre stretch, according to Mr Sawyer.

"In the late dry season there are thousands of cane toads," he said.

"And if you look at the water, in some of the remnant waterholes, it is a black soup of tadpoles."

Parks Australia does 'nothing to mitigate problem'

Mr Sawyer believed the problem stemmed from a lack of action by the Canberra-owned Parks Australia, who has responsibility over Kakadu National Park.

"The biodiversity's been decimated in recent times, and I can't point to anything that I'm aware of that Kakadu's done to try and mitigate that," he said.

In 2018, Kakadu National Park rangers opted to do away with active toad management strategies.

Graeme Sawyer hasn't seen any olive pythons on his recent trips to Kakadu. ( Supplied: Teonie Dwyer )

Kakadu National Park's then-biodiversity manager Anthony Simms told the ABC at the time there "is no way of effectively managing toads".

"It is a complete and utter waste of time," Mr Simms said.

He said ecosystems were recovering on their own, citing increases in the populations of emus and northern quolls.

The park not only discontinued its toad management strategies but also its program that tried to train northern quolls not to eat toads.

"As an institution as Kakadu, we found the results inconclusive and we weren't convinced enough that it was worth the while of the financial investment, and some of the animal welfare issues that go with the training to pursue that program," Mr Simms said.

Kimberley Toad Busters found community action works

Eileen Scott-Virtue, another cane toad expert and founder of the Kimberley Toad Busters, told the parliamentary inquiry that management strategies had worked, and front-foot community action against the toads in the north-west town of Kununurra had meant "that we did not have quite the biodiversity loss or impact on our large vertebrate animals that happened in Kakadu National Park".

"We have had probably a faster recovery rate of some of those larger vertebrates animals, and without community action I do not believe that this would have been possible," Ms Scott-Virtue said.

Parks Australia was contacted for comment.

Public hearings for the inquiry into controlling the spread of cane toads continue today in Canberra.