A rare shark has been discovered in the Northern Territory but a controversial water allocation plan has sparked fears it may be "lost forever".
The speartooth shark is considered critically endangered; however, dozens have been found in the muddy waters of the Roper River.
Rangers have helped researchers study about 40 speartooth sharks which usually live in limited numbers in tropical rivers across northern Australia and Papua New Guinea.
A survey indicated the shark lived in a limited area of the Roper River, sparking fears it might be affected by the largest water allocation plan in the NT's history.
The NT government released the Georgina Wiso Water Allocation Plan in November, allocating 210 billion litres - about the same as 100,000 Olympic pools - for extraction per year.
It has been the subject of criticism from environmental groups and traditional owners, who hold fears it could cause the Roper River to stop water flowing.
Charles Darwin University's Dr Peter Kyne said the speartooth shark population could be threatened by changes to their environment, making it important to understand the water plan's impact on the Roper River.
"If we don't then this unique and isolated population that call the Roper River home could be lost forever," said Dr Kyne, the CDU's Institute for Environment and Livelihoods senior research fellow.
CDU PhD candidate Julia Constance has been researching speartooth shark movements in the Roper River.
She said the females returned to the same rivers they were born in to have their own pups.
"The speartooth shark is quite elusive and occurs in very particular habitats," she said.
"This can make them very susceptible to changes in their environment."
Ms Constance has worked with Yugul Mangi rangers from Ngukurr in her study of the speartooth shark in the NT river.
Rangers helped scientists with their survey, helping catch about 40 sharks, with genetic samples taken from each one before they were released back into the river.
Ms Constance said the rangers would have an ongoing role in protecting the shark in the river.
