In October last year, Rak Mak Mak Marranunggu woman and traditional owner Linda Ford and her family made a concerning discovery while out hunting magpie geese.

"While the fellas were off goose shooting, we were out looking for long neck turtles and we found a small area that had lots of [Northern long-neck] turtle shells and I thought that was really unusual," she said.

Ms Ford found the shells at her family's property Twin Hill Station, about two hours south-west of Darwin.

It was not the first time people had been worried about the turtles, she said.

About 10 empty long-neck turtle shells were found over one day at Twin Hills station. ( Supplied: Isabel Ely )

"Some of the turtles' traditional owners have found over the years have had green fat, so we don't know what causes that and some of them have been a bit skinny, but that also depends on the season as well," Ms Ford said.

Ms Ford said the discovery was particularly concerning because turtles hold a special place, culturally, for her family.

"There's a dreaming site of significance for turtles here and a lot of our children have them as their conception totems so they're part of who we are," she said.

"The turtle is quite significant to us in the way that we understand our world so want to be able to look after it."

After finding the shells, Ms Ford reached out to Territory Natural Resource Management Group who put her in touch with researchers from Charles Darwin University to help investigate the cause.

"This is the second time we've come here, we did find some dead turtles and it's kind of a mystery," turtle researcher Dr Carla Eisemberg said.

Families of locals from Twin Hill station helped researchers find live turtles to test to try and find out what is killing them. ( ABC News: Georgia Hitch )

"We don't know why they're dying or even if it's natural causes but it will be very interesting to know what's happening, so we are very early stages of our research right now."

Toxins leaching into water among theories

While the exact cause is a mystery, there are concerns it could be the result of toxins slowly leaching into the water.

"There's a lot of aquatic weeds in this floodplain," water quality expert Dr Erica Garcia said.

"Herbicides get used to try and control those weeds so whether it's the herbicides from weed control or heavy metals from leftover from rum jungle mine we will be looking at that.

"This is a first. I've not looked at a sort of CSI situation where we're trying to figure out this mystery of what's happening with the turtles - it's a fun exciting new area of research for me."

Turtles 'avocado of bush meat world'

Dr Eisemberg said figuring out what was leading to the turtles' ill-health was important, and could have wider implications.

"They are an important source of bush tucker so people like eating them and there are many reasons for that," she said.

Researchers became involved after Traditional Owner Linda Ford (right) raised the alarm. ( ABC News: Georgia Hitch )

"I like saying that turtles are the avocado of the bush meat world because they are green and they are full of good fats," she said.

"So we are trying to not just make sure that the turtle population's healthy but also healthy for people to be able to harvest them and eat them."

To collect samples the scientists were invited on a 'turtle hunt' with traditional owners, but unfortunately after a day and a half could not find a live turtle.

They are now organising a second trip where hopefully, once a turtle is caught, they will collect samples of its flesh and liver to test for toxins, as well as water and bug life from the areas near where they have been living.