Otago Fish & Game has been surveying Southern Lakes tributaries for spawning land-locked Chinook salmon for the past five years.
Surveys found salmon spawning sites in the Hāwea and Wakatipu catchments, but the location of Wānaka sites remained a mystery until now.
"We’re relieved to finally locate one of the spawning locations for Lake Wānaka salmon," Cromwell-based Otago Fish & Game officer Mason Court said.
"While Lakes Hāwea and Wakatipu have productive salmon fisheries, the Wānaka salmon population has been struggling."
The spawning salmon were spotted this winter in an unnamed tributary of the Makarora River during an on-foot survey of possible historic spawning locations.
"We can now work with landowners and other agencies to assess how we can improve this stream’s conditions to support salmon spawning in the Wānaka catchment."
Fish & Game officers would continue the search for other Wānaka salmon spawning streams.
Previously, the organisation had taken eDNA water samples from Makarora River to work out the upper limit of the salmon population. Although the samples had tested positive for the past two years, spawning salmon had not been seen.
"Land-locked salmon are smaller than sea-run salmon, and therefore are harder to spot using a helicopter.
"Another challenge is that, like all Pacific salmon, Chinook salmon die after spawning, and their remains are quickly consumed by birds, mammals, trout and eels".
Chinook salmon were introduced to some South Island rivers from California in 1901 and began spawning, creating a valued sports fishery.
The salmon in the Southern Lakes have been landlocked since Roxburgh Dam was built in 1953 and are among of the purest strains of the species in the world.
The bright-silver fish range in size from only 500g to 1kg and are highly regarded for their eating qualities.
"The Wānaka salmon population declined in the early 2010s due to unknown reasons."
Under a 10-year management sports fish plan, Otago Fish & Game committed significant resources to the Upper Clutha salmon fishery.
In the 2020-21 season, surveys recorded only 17 salmon caught by anglers in Lake Wānaka, Mr Court said.
