By Phil Mercer
BBC News, Sydney
Saltwater crocodiles are larger and more aggressive
Freshwater crocodiles are being driven out of parts of Australia's Northern Territory by their more aggressive saltwater cousins, researchers say.
Scientists believe the freshwater species could slowly be disappearing.
Government research has shown the number of freshwater crocodiles has dwindled in some Northern Territory rivers since the late 1990s.
Eating toxic cane toads is thought to be contributing to their demise, and climate change may also be a factor.
Any fight over territory between saltwater and freshwater crocodiles is likely to see only one winner.
Saltwater crocs are the world's largest reptiles, growing to average length of four metres (13ft). They are arguably Australia's most dangerous animal.
The freshwater variety, however, is far more timid and attacks on people are almost unheard of.
These smaller creatures are usually about 1.5m (5ft) long, while their diet includes fish, insects and the occasional mammal.
They will also eat poisonous cane toads, which some researchers believe is also threatening their long-term future.
Conservationist Sandy Boulter says many crocodiles have been no match for the toads' deadly toxins.
"We found a lot of freshwater crocodile carcasses and if the carcass was fresh enough we would cut it open.
"We found between one and three cane toads in the crocodiles' stomachs and the crocodile had died quite quickly and so we know that, well, one or two sizeable cane toads can kill quite a sizeable freshwater crocodile."
Others experts have suggested that the effects of warming temperatures may also be threatening the freshwater crocodile.
They are concerned that a shifting climate has the potential to disrupt the species' breeding cycle.
Under a new government management plan, the number of these reptiles in the Northern Territory that can be taken from the wild for their skins has been sharply cut.