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.
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 over 150 South Island Rivers, but is not in the North Island. Under the Biosecurity Act 1993, the entire South Island is a Controlled Area. This means 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 moving between waterways, and treat every waterway like it is infected with didymo.
Didymo can attach itself to stream, river and lake beds 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.
Page last updated: 27 July 2012