Invasive water weed spreads to Buller River 

An invasive water weed, commonly known as rock snot, has been found in the Buller River, it was confirmed today.

Biosecurity New Zealand (BNZ) said in a statement today it was investigating a confirmed find of didymosphenia geminata (didymo), in the West Coast river.

BNZ asked all river users to avoid the Buller if they also intended using other rivers.

"It is likely that a controlled area will be declared on the Buller in the next few days, prohibiting use of the Buller River if users are intending to use other rivers," BNZ didymo response manager Kerry Bodmin said.

Didymo has been declared an unwanted organism under the Biosecurity Act 1993.

Among other things, it can affect stream habitat and sources of food for fish and make recreational activities unpleasant.

It is not a human health risk, though swimmers might notice itchy eyes or irritated skin from the silica in the algal cells.

Ms Bodmin said BNZ was working with local councils, the Conservation Department and Fish and Game to identify and contact river users and was aware that the fishing season began Saturday and that the whitebaiting season had already started.

She said didymo was first identified in Southland's Mararoa and lower Waiau Rivers in October last year -- the first time it had been found in the Southern Hemisphere -- and extensive public awareness was carried out to try and contain the spread.

A controlled area was declared on the Southland rivers on August 19.

The discovery of the weed in the Buller River was the first find outside Southland.

But the possibility didymo might be in other South Island rivers was acknowledged and BNZ would be working to gather further information, Ms Bodmin said.

Didymo is microscopic and can be spread in a single drop of water.

In bloom, it attaches itself to the streambed by stalks to form streamers that can turn white at the ends.

Larger blooms form a thick white or brown layer that smothers rocks, submerged plants or other materials.

The algae looks slimy, but feels like wet cotton wool. When washed up on stream banks it looks similar to clumps of wet tissue paper.

- NZPA