Media release

Don’t spread unwanted freshwater pests this summer holiday season

Tuesday 18 December 2018

With the summer holiday season now underway, Otago Regional Council and the Ministry for Primary Industries are reminding everyone living in or visiting Otago and the Southern Lakes of the importance of cleaning their equipment between waterways to avoid the spread of unwanted freshwater pests including the invasive algae Didymo.

Unwanted freshwater pests such as Didymo, Lake Snow, and Hornwort pose a serious threat to our rivers, streams and lakes.

“Once in a waterway they can disperse rapidly and destroy the environmental, recreational and aesthetic values of our waterways,” says Otago Regional Council (Acting) Director Environmental Monitoring & Operations, Peter Winder.

“We ask people going between waterways to Check, Clean, Dry any equipment that has come into contact with river or lake water. Some freshwater pests, like didymo, are microscopic and can be spread by a single drop of water. Even if you can’t see the danger you could be spreading it.”

Mr Winder says before leaving a waterway, everyone should check their items for any weed or debris and leave it at the waterway they found it in.

All items including togs, fishing lines, jandals, boats and anything else that has made contact with water should then be cleaned for at least one minute with a five percent solution of biodegradable dishwashing solution. That’s about one tablespoon of detergent per 250ml.

Water absorbent materials such as lifejackets, wetsuits and boots require longer soaking times to allow thorough saturation.

Drying will kill didymo, but even slightly moist items can harbour didymo and other microscopic pests for months.

To ensure didymo cells are dead by drying, the item must be completely dry to the touch, inside and out, then left dry for at least another 48 hours before use.

Mr Winder said, “Following these simple procedures will help slow freshwater pests like didymo from spreading throughout New Zealand waterways. It’s everyone’s responsibility to try to preserve the environmental integrity of our waterways for future generations.”

For more information about didymo and freshwater pests go to or visit



Martin King

ORC Manager Environmental Services

027 487 9991


Emma Schranz

ORC Senior Media Advisor