This microscopic pest can be spread by a single drop of water. Even if you can't see it, you could be spreading it.

The algae is native to northern Europe and North America, and was first reported in New Zealand in 2004. Since then, Didymo has been confirmed in various lakes and rivers across Otago, however, are many waterways in New Zealand that still require safeguarding. The Ministry for Primary Industries has declared the South Island a Controlled Area for Didymo. This makes it a legal requirement to clean all gear used in the water before going from one waterway to another.

Didymo is not yet present in the North Island of New Zealand.

• It forms a thick pinkish-brown layer that smothers rocks and submerged plants in freshwater.
• Didymo can establish in streams, rivers and lake beds and rocks by stalks.
• It can form flowing ‘rat tails’ which are woolly, white-cream at the end. These can resemble soggy toilet paper in the water.
• While Didymo appears slimy, the texture feels like wet cotton wool.

To prevent the spread of freshwater pests, including didymo, whenever you move between waterways you must check, clean and dry any equipment that comes into contact with water. 

Before you leave any river or lake:

Check - remove any plant matter from your gear and clothing and leave it at the site. Don’t wash plant material down the drain. 

Clean - soak or scrub all items using one of the below treatments:

Note: 60° C is hotter than most tap water; 45°C is uncomfortable to touch. Allow longer times for absorbent items. 

Dry - ensure your gear is completely dry to touch, inside and out, then leave to dry for at least another 48 hours before you use it. Didymo can survive for months on moist gear.  

If it’s wet, it’s a threat. 

Remember to check, clean and dry all equipment, before you leave any lake, stream or river.