Didymo

Legal status: Unwanted Organism (under the Biosecurity Act 1993). It is an offence to knowingly spread an unwanted organism with penalties of up to 5 years imprisonment, and/or a fine of up to $100,000.

Status: This organism is being investigated in New Zealand. Possible sightings should be reported to 0800 80 99 66.

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Didymosphenia geminata (didymo), also known as "rock snot" is a freshwater diatom (a type of alga) and was first reported in New Zealand in the Lower Waiau River in 2004. Didymo is currently found in a number of South Island Rivers. Biosecurity New Zealand has since declared the entire South Island a Controlled Area for Didymo. This means waterways remain open to angling and other recreational activities, but people are legally obliged to prevent the spreading of didymo.

Didymo is a microscopic pest that can be spread by a single drop of water. Even if you can't see it you could be spreading it. Therefore to prevent the spread of didymo you must Check Clean, Dry your gear when going from one waterway to another, everywhere in New Zealand. It is in New Zealand's best interests for you to treat every waterway like it is infected with didymo.

Didymo sometimes forms massive blooms on the bottom of the streams, rivers and lakes. It attaches itself to the stream bed by stalks, and can form a thick brown layer that smothers rocks, submerged plants and other materials. It forms flowing 'rats tails' that can turn white at their ends and look similar to tissue paper. As the 'tails' of the alga get longer they become white in colour.