An algae species that can create troublesome, mucus-like strings known as lake snot has likely now spread to Lake Taupō.
The discovery - made from historic samples taken from the Central North Island's Moawhango River - has prompted a new plea for anglers and hunters to check, clean and dry their equipment.
The microscopic Lindavia intermedia is an extremely small freshwater algae species that floats in the water column of lakes and has the potential to create lake snot, which poses no known health threat but can clog fishing and boating equipment.
Its detection, revealed by Niwa researchers who were testing historic water samples to determine when lake snot first arrived in New Zealand, came a decade after it was found in the North Island for the first time, at Lake Waikaremoana.
The problem has been much more pronounced in the South Island, where it has spread from lake to lake.
After Horizons Regional Council staff were told of the latest case last month, further investigations indicated it was also present in Lake Rotoaira and Lake Taupō.
Testing was also underway on water samples collected from lakes downstream from Lake Taupō.
Horizons Regional Council's samples from Lake Otamangakau have come back clear, however the council would undertake additional testing at popular fishing and recreational waterways such as lakes Wiritoa, Dudding and Namunamu.
Where Lindavia intermedia had been found, it was likely this algae species has been in these lakes for more than a decade, as historic samples recently retested came from as far back as 2005.
"Over that time, the Lindavia intermedia has not produced lake snow effects as far as we are aware and we have no evidence of it causing issues to lake users," Horizons freshwater scientist Michael Patterson said.
"There is currently no known way of removing Lindavia intermedia once it is present in a lake or waterway.
"The conditions necessary to produce the lake snow effect are not clear, more research is needed."
Waikato Regional Council biosecurity officer Paul Quinn said as lake snot produced mucus-like strands of slime which hung and drifted under the water, it could stick to fishing gear, boat hulls, swimmers, and clog boat, industrial and domestic water supply filters.
While other waterways may also have Lindavia intermedia, rivers and streams with fast moving flows were believed to be less than ideal environments for the algae to thrive.
Both councils were looking at options for adding Lindavia intermedia testing to their regular monitoring programmes and are working with stakeholders and researchers to find out more about what conditions influence the growth of the algae.
"In particular, we are keen to understand what causes it to produce lake snow like it has in some South Island lakes."
Fish and Game spokesperson Don Rood said Lake Taupō and neighbouring waterways were extremely popular trout fisheries, and provided a "huge" recreational and economic benefit.
"Trout angling is not only highly valued by Kiwis, but these fisheries also earn many millions of dollars in tourist revenue," Rood said.
"We need to do all we can to protect this valuable recreational asset."
Hunters using boats on Central North island lakes were urged to check, clean and dry their equipment, particular boats, motors and trailers.
"Spraying them with a five per cent solution of dishwashing detergent or nappy cleaner will do the trick, or a two per cent bleach solution," Rood said.
"And be especially cautious if travelling to another lake or river."