Cane toads have wiped out some populations of dwarf crocodiles in northern Australia.

Charles Darwin University researchers have been investigating the impact of the toxic toads on Australia's smallest freshwater crocodiles.

Their studies have centred on upstream escarpments around the Victoria and Bullo rivers.

Dr Adam Britton says the dwarf crocodiles found in upstream stretches of the river are small because their growth is stunted by a lack of food.

The spread of the introduced cane toads through the Top End has seen a plentiful but deadly addition to their diet.

The population of the crocs, sometimes referred to a pygmy crocodiles, is thought to number in the hundreds.

Dr Britton says steps need to be taken to ensure the survival of the unusual crocodiles, which rarely reach more than one metre in length.

"We really don't know whether these cane toads are going to wipe them out completely," he said.

"We know that the initial impact of the toads is very severe.

"The question is, will the crocodile populations be able to deal with this and be able to recover?"

Dr Britton says the spread of the cane toads presents a significant conservation issue for the entire upstream escarpment ecosystems of northern Australia.

He says recent research had raised questions about why the toads have wiped out some populations but left others largely unaffected.

Possible evidence had been found that dwarf crocodiles could adapt their behaviour to only eat the back legs of the toads, avoiding the deadly bufotoxins secreted in their bodies.

The team is conducting further research into the genetics of the dwarf crocodiles to better understand the long-term impact of cane toads on their populations.