The confirmation of didymo in the lower Cass and Macaulay rivers at the top of Lake Tekapo has the Department of Conservation worried about the potential for the invasive algae to spread further into the upper Tekapo catchment.
It was very important to keep didymo out of the upper Cass, upper Macaulay and Godley Rivers, said Twizel-based biodiversity assets programme manager Dean Nelson.
"These waterways are examples of prime braided river habitats and it would be devastating to see didymo become established in them," he said.
The thick smothering mats seen in other didymo-affected rivers could impact significantly on the habitat and food sources of native birds and fish.
Riverbed birds such as the nationally critical black stilt/kaki and the threatened wrybill/ngutu pare and black-fronted tern/tarapirohe feed around the shallow river braids of the upper Tekapo catchment waterways.
The catchment is a popular area for recreational activities including mountain-biking, hunting, fishing, four-wheel-driving, boating and tramping.
To ensure didymo was not further spread up the catchment, Mr Nelson encouraged all waterway users to decontaminate.
• In April, Kurow-based Central South Island Fish and Game officer Graeme Hughes reported didymo was disappearing in some parts of the Waitaki River.
When contacted yesterday, Mr Hughes said it had been a common observation by river users that it was not appearing to be thriving.
However, it had "sprung away" in late winter-early spring, with as much vigour as it had when it was first discovered in the river, which was disappointing.
