Recent tests for didymo in 19 Fiordland National Park rivers have come back negative, a pleasing result for Fish and Game and Department of Conservation (Doc) staff.
Didymo, a clogging algae also known as rock snot, is well established at several sites in Southland and the eastern boundary of Fiordland National Park, including Lakes Te Anau and Manapouri and the Eglinton and Waiau Rivers.
Each year, Fish and Game and Doc collect water samples from previously uncontaminated rivers and send them to Niwa for analysis.
This monitoring work enables Doc and Fish and Game to assess the effectiveness of approaches for controlling the spread of didymo and to make changes, such as installing additional cleaning stations, as required.
Doc biodiversity ranger Sanjay Thakur said the fact this was the second year running with no record of didymo spread was good news and showed the "check, clean, dry" campaign had been effective at stopping the spread of didymo in Fiordland.
"Unfortunately, once didymo is established in a waterway there is no known way to get rid of it, so the best we can do is try to keep didymo out of unaffected rivers and lakes.
"These results confirm that this is an achievable goal, and as long as anglers, trampers, hunters and other users continue to check, clean and dry their gear, Fiordland's waterways should remain pristine for many years to come," Mr Thakur said.
"Most of the rivers selected for monitoring are either popular with anglers or associated with tramping tracks, such as the Clinton and Arthur Rivers along the Milford Track, and receive large numbers of recreational users over the summer season."
Mr Thakur said the didymo-free waterways were "entirely thanks to people's willingness to take a moment to check, clean and dry their gear.
"Concessionaires, such as Real Journeys and Ultimate Hikes, which bring large numbers of visitors into contact with Fiordland's precious waterways, also deserve much of the credit for ensuring that their clients all clean their boots before setting out," he said.
More information about didymo is available at the Fiordland National Park Visitor Centre.
Simple, lightweight didymo cleaning kits are available to buy, and a cleaning station is available for public use free of charge upon request.
