The Southern Hemisphere's only population of the mysterious sockeye salmon is back from the verge of extinction.
More than 1000 sockeye have been counted in the Twizel River, just north of the South Island township, as they make their great migration upstream to spawn.
Once thought to be extinct in New Zealand waters, they have returned in big numbers.
"Within this stretch of the Twizel River we have seen 300 to 400 fish," says Fish and Game officer Jayde Couper.
The salmon are the only fish of their type in the Southern Hemisphere and the annual migrating has attracted plenty of tourists, including keen Christchurch angler Rob Clark.
"Pretty much anywhere you put your head through the bushes, there was a whole load of little salmon doing their business," he says.
They are four years old, average at 1.5kg and are at the end of their life cycle.
Released into waters in 1901, there were plans to create a sea-run salmon canning industry.
But they never made it to the ocean and were instead landlocked by the dams in the Waitaki Lakes District, before disappearing in the 1980s.
"It's a mystery to where the sockeye were in that period but we assume there were small populations remaining in the lakes," says Mr Couper.
They've now been found in Lake Pukaki beneath Aoraki Mt Cook and are hard to catch.
"I think it is absolutely fantastic, it's a testament to water quality," Mr Clark says.
"Why would you want to catch them? I have no idea - as a table fish they are of no value."
More than 1000 fish have been counted in the area, where they will lay more than 2000 eggs each.