The invasive weed didymo has been found in the lower reaches of North Otago's Kakanui River and threatens one of the country's most threatened fish.
The Department of Conservation is concerned about the impact on the lowland, longjaw galaxias which finds its last refuge in a tributary of
the Kakanui, the Kauru River.
DOC freshwater ranger Pete Ravenscroft said at this stage didymo was an unknown threat to the longjaw, but it had the potential to be very significant.
"If didymo behaves the way that it has in some rivers and smothers the river bottom and substrate, where the tiny fish feed, breed and find refuge, then it could lead to the extinction of the species."
That meant every effort needed to be made to prevent the algae getting into the Kauru.
DOC and the National Institute of Water and Atmospheric Research (Niwa) on behalf of Biosecurity New Zealand would start a feasibility study of the Kakanui River tomorrow.
"This is to gauge where didymo is in the Kakanui and whether or not the invasive water weed can be controlled in that river," Mr Ravenscroft said.
If control was possible, this could reduce the risk to the threatened fish.
A report on the feasibility of control should be available by the end of next week.
In the meantime DOC urged people to keep out of the various parts of the Kakanui River system.
- NZPA
