A search is underway in southern New South Wales waterways to find a potentially extinct species of fish last recorded in the wild 20 years ago.

Key points: The Kangaroo River perch has not been recorded in the wild in 20 years

The Kangaroo River perch has not been recorded in the wild in 20 years Scientists will use advanced technology to DNA test waters in their search for the fish

Scientists will use advanced technology to DNA test waters in their search for the fish If it is not found, it will be Australia's first freshwater fish to become extinct

Lurking beneath the waters of the Shoalhaven River is a small, silvery grey perch that has been part of the area for thousands of years.

At least, people hope it is still there.

Scientists and anglers are on a mission to see if the Kangaroo River perch still exists and if it is not found, it will become Australia's first extinct freshwater fish.

"I value it because it's part of the rivers I grew up around," NSW Department of Primary Industries (DPI) Fisheries manager Erin Lake said.

"It's a species that's part of the culture; it was a significant species for thousands of years to Aboriginal people and people as recently as 1998 when it was last recorded.

"People got a kick out of seeing it and were amazed this little perch species was here."

The Kangaroo River perch is identified by its silvery grey colour with a mottled pattern and white eye. ( Supplied: OzFish )

The hunt is now on to either catch a Kangaroo River perch for documentation and then release it, or find the DNA of it in the water.

Human intervention to enable survival of species

New technology now allows scientists to use the genetics of the fish, which they have on file, to test against the DNA they sample in the Shoalhaven River systems.

"The fish has been caught and we've captured the genetics of it, so we have what's called a 'primer'," Ms Lake said.

Ms Lake is passionate about fish ecology in the Shoalhaven, having lived there for 20 years. ( ABC Illawarra: Justin Huntsdale )

"You put that in a machine and if that DNA pops up, it's a match.

"Any species in the water leaves a trace and this technology allows us to take multiple samples in the field and take them back to the lab [so] you can sample a lot of a large area."

The end goal for finding the Kangaroo River perch is not only to rediscover a lost species but improve its habitat.

It would also be listed under state and national law as a threatened species.

Ms Lake said this type of work was essential for preserving Australia's native creatures.

"A lot of species now in our environment need active management," she said.

"The landscape has changed and a lot of people don't know [that] species won't survive without human intervention.

"Our interventions can have a positive impact on its conservation and potentially bring it back to these areas so people can see it again."

Anglers turn citizen scientists in search for perch

Not-for-profit organisation OzFish is calling for anglers to come forward with any stories or photos they have of the Kangaroo River perch.

They are also looking at crowdfunding their efforts to send scientists into the field.

The Kangaroo River perch is unique to the Shoalhaven area of New South Wales. ( ABC Illawarra: Justin Huntsdale )

The fish is silvery to dark grey in appearance, and sometimes with a mottled pattern, a prominent lateral mid-line, and a white eye.

"Most anglers are aware of the Macquarie River perch and nearly all are always fishing for catch-and-release," OzFish founder Craig Copeland said.

"They'll generally throw it back, but we want them to take a photo of it and report it.

"We've had anglers over the last six months reporting back to us and that's helping direct the department, which is good information."

The DPI is also looking to speak to landholders with properties backing onto the Kangaroo River who are happy to have scientists test for perch on their properties.

"The fish could be extinct but it's worth another look," Ms Lake said.

"People should love their Australian wildlife more than they do because there are so many amazing species of fish and mammals and birds and learning about them and loving them is something we need to do."