Whanganui River. Photo: LDR / Moana Ellis
The Department of Conservation (DOC) is calling on the public to help solve a mystery that's led to mass fish deaths in Whanganui.
DOC has received reports of dead fish, including tuna, in the Whanganui River catchment.
In a statement, it said the mass deaths of tuna, eels and other fish have been reported in the upper Whanganui River in previous years, typically in summer.
The public were asked to report any sightings of sick, dead, or dying fish to the Ministry for Primary Industries' pest and disease hotline (0800 80 99 66).
River restoration ranger Jane Taylor said they needed teamwork to solve the mystery. She said it was especially important as the long-fin eels found in the catchment were at risk of extinction.
Biosecurity New Zealand aquatic health team manager Mike Taylor said they wanted people to take photos as well as report the location, number, date and species.
Members of the public should also report the freshness of the fish, he said.
"This will help us consider whether there are suitable specimens to test for diseases."
Te Mana o Ngā Tuna chairperson Ben Potaka said mana whenua had been concerned about the annual mass deaths of tuna in the Whanganui for years, but nothing had been done about it until now.
"Tuna are significant taonga," he said. "It's time for everybody to all pull together to try and understand the cause of these mass fish deaths."
DOC urged the public to exercise common sense, and not take dead or dying fish to eat while the cause of their deaths is undetermined.