Department of Conservation contractor Paul Van Klink and his conservation dog Hoki conducted a survey of whio on the Routeburn a week ago.
Mr Van Klink and his dog were flown in by helicopter to the survey area and over a 24-hour period they found four pairs of adult whio and six juvenile birds.
There could have been more birds in other parts of the river, he said.
"It is a fantastic recovery, when you consider that when I started doing this whio survey work in 2012, I found only six birds in five catchments."
Whio are found only in New Zealand and live on fast flowing rivers.
They are more easily seen on the $10 note than in the wild.
Habitat destruction, forest clearance and chick predation by stoats are the biggest threats to the continued survival of the whio.
Mr Van Klink said intensive predator trapping, 1080 aerial bait drops and the introduction of additional juvenile whio birds bred through the Whione nest egg programme have all contributed to the increased numbers of breeding pairs and ducklings found on the Routeburn and Rockburn.