The national didymo survey is almost complete, with no further finds of the invasive alga known as rock snot.
Biosecurity New Zealand said the last find was reported a week ago from the Von River near Queenstown, bringing the total known affected rivers to eight.
However, river users should not
assume any river to be free of didymo and should continue to clean items that have been in contact with water before using in any other waterway, Biosecurity spokeswoman Amelia Pascoe said
Didymo was confirmed in the Mararoa, upper and lower Waiau, Oreti, Buller, Hawea and upper Clutha rivers before the national survey began on October 2.
It has since been confirmed in the Von River, which flows into Lake Wakatipu.
Amelia Pascoe said the results were good news, but did not guarantee that other rivers were free of didymo.
"As we've said from the beginning of this response, river users throughout New Zealand need to clean their equipment between waterways or didymo will spread," she said.
"This is a personal-responsibility issue. New Zealanders need to treat rivers with more care and ensure that they practise good river hygiene at all times."
A significant public awareness campaign has been expanded to form part of the established National Aquatic Weeds Awareness Campaign.
Didymo is an invasive Northern Hemisphere alga.
It was first reported in New Zealand in Southland's Mararoa and lower Waiau Rivers in October 2004. It is not known how it arrived in the country.
In bloom, didymo forms large, unsightly brown mats, sometimes with streamers, that smother the riverbed, affecting food sources for fish and making water recreations unpleasant.
- NZPA
