Didymo found in upper Clarence River

The invasive alga didymo has been detected in the upper Clarence River, MAF Biosecurity New Zealand announced today.

The find was the result of anglers fishing in an area downstream of Jack’s Pass turn off, reporting suspicious algal growths.

A sample taken from the site was confirmed positive by macroscopic and microscopic identification.

MAF Biosecurity New Zealand didymo response manager Chris Bicknell said the find was disappointing and highlighted to the need for freshwater users to ‘Check, Clean, Dry’ all items between waterways to prevent the spread of didymo and other aquatic pests.

Marlborough District Council senior biosecurity officer Dave Grueber said the Clarence River find increased the potential for river users to spread didymo into other rivers in Marlborough, a region which until now was not known to be infected with didymo.

"The ‘Check, Clean, Dry’ process must be employed by all river users” he said.

The Department of Conservation is urging people driving on the Rainbow Road through Molesworth and St James’s stations to use bridges and not fords to cross creeks on the route that are part of the Clarence catchment.

“This will reduce the risk of didymo being spread into the Wairau River catchment by vehicles as past Island Saddle there are creeks feeding into the Wairau that can only be crossed through fords,” said DOC South Marlborough area manager Dave Hayes.
Nelson Marlborough Fish and Game manager Neil Deans described the latest find as “disappointing but not unexpected”.
“The potential for spread into the nearby upper Wairau and Acheron catchments is now very high and those using the area and even traveling through and using vehicle fords need to take utmost care,” he said.

Felt-soled waders have been identified as a high risk of spreading didymo and Chris Bicknell suggests anglers use rubber-soled footwear instead, which are easier to clean and dry.

More information on didymo and approved cleaning methods can be found on the MAF Biosecurity New Zealand website www.biosecurity.govt.nz.