The invasive algae didymo is continuing to spread in the South Island. It has been found in six more waterways in Nelson.
The algae has been discovered in the Waimea River at Appleby Bridge and in five tributaries of rivers which are already infected in Buller, Motueka and Golden Bay.
The annual survey also found didymo further up Marlborough's Wairau River at the Rainbow Bridge.
A didymo management group for the top of the South Island says river users should always check, clean, and dry gear when moving between waterways.