Neil Deans of Fish & Game reports that, the organism has been found near [the Buller’s] source at Lake Rotoiti and also at a distance of some 30km downstream. Biosecurity New Zealand is in the process of declaring the mainstem Buller River a controlled area under the Biosecurity Act. Anyone entering or using the waters in this controlled area is restricted to those waters alone. In other words anglers or kayakers, for example, cannot fish or paddle the mainstem Buller River and then go to any other waters. Only a single drop of water is required to transfer didymo between catchments.
If you have recently kayaked on the Buller, please immediately clean and dry your equipment using the recommended cleaning and drying methods. Didymo has been previously found in Southland’s Mararoa and lower Waiau Rivers.