Scientists have uncovered 66 fish of a species once thought to have died out in Victoria.
They will now start a captive breeding program for the purple spotted gudgeon, a small colourful native fish declared extinct in the state in 1998.
Group chair Adrian Martins said members could not believe it when they started finding so many.
"Most of our team have worked their whole lives dealing with the decline of threatened or endangered species, so to have an opportunity to be witnessing the opposite is something special," she said.
The team was brought together after the 2019 discovery of a handful of purple spotted gudgeon in Third Reedy Lake.
It has also found the fish at nearby Kangaroo Lake and Racecourse Lake and is creating a long term protection plan for the species.
The group is planning to run more eDNA sampling to see if there are any more purple spotted gudgeon populations further afield in Victoria.
"The aim is to help establish populations in other parts of the state and the Murray Darling Basin," Mr Martins said.
"We have a great chance now to not only bring the southern purple spotted gudgeon back from the brink, but to help build its numbers and distribution back up to what they were before European occupation, river regulation, and the introduction of pest species."
The discovery of the large population at Middle Lake will also allow water authorities to carry out a series of water savings works put on hold at Third Reedy Lake when the fish was rediscovered.