The invasive algae didymo has been found in the Cobb River in Kahurangi National Park.
The Department of Conservation says it is concerned it could be spread to more rivers in the park and might impact on endangered native whio/blue ducks.
The didymo cells have been found in samples taken from the Cobb River near Trilobite Hut in Golden Bay in a DOC didymo survey. DOC intends to carry out further sampling to determine the extent of the spread of didymo in the Cobb River catchment.
The department and MAF Biosecurity New Zealand are reminding people to 'Check, Clean, and Dry' their gear between waterways to prevent the spread of didymo to other rivers in the national park and elsewhere.
DOC Acting Golden Bay Area Manager, Hans Stoffregen, said the find of didymo in the Cobb River within Kahurangi National Park was very disappointing and concerning.
"Kahurangi National Park has beautiful, pristine rivers that we would not want to see blighted by didymo. These rivers provide habitat for our unique native aquatic flora and fauna. Whio live on a number of rivers in the park and we are particularly concerned about the potential impact of didymo on whio if didymo gets into those rivers.
"While the long term effect on invertebrates and whio is unknown, didymo can form dense mats which may affect invertebrate populations. Invertebrates are a food source for whio.
"Kahurangi has a number of popular fishing rivers, including the Cobb. We are appealing to people fishing or carrying out other activities in the park's rivers, particularly the Cobb River, to make sure they 'Check, Clean and Dry' their gear between waterways.
"Trampers are asked to avoid contact with the Cobb River water and as the track runs alongside it they won't need to cross it. If any boots, socks or other gear are put in the river then these should be cleaned afterwards using 'Check, Clean and Dry' procedures before being put in any other waterway. Wherever possible, trampers should use bridges to cross waterways.
"People recreating in Kahurangi National Park have an essential role to play in preventing the spread of didymo within the park and helping to protect the park's pristine rivers, freshwater biodiversity and native blue ducks."
MAF Biosecurity New Zealand didymo response manager Chris Bicknell said the find highlighted the need for every fresh waterway user, no matter where they are, to 'Check, Clean and Dry' their gear between waterways.
"Individual water way users have a crucial role in slowing the spread of didymo and other aquatic pests. 'Check, Clean, and Dry' is our best defence.
"Before leaving a waterway, people should check items and leave any debris they find at the waterway. All items should then be cleaned for at least one minute with a five percent solution of dishwashing liquid or nappy cleaner.
"Water absorbent materials such as felt-soled waders and boots require longer soaking times to allow thorough saturation."
The DOC didymo survey in Nelson, Marlborough and Kaikoura, taking place in conjunction with a MAF Biosecurity New Zealand didymo delimiting survey, is testing for didymo in around 70 rivers. Rivers being surveyed include those considered to be at high risk of didymo infestation or which have high biodiversity values. Only a few rivers are still to be tested and to date the only new find of didymo from the survey has been in the Cobb River.