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Didymo (Didymosphenia geminata) is an invasive freshwater valgae which is present in some South Island rivers in New Zealand.

Didymo is most likely to be spread by humans moving items between waterways.
To ensure you don’t spread didymo, wherever possible restrict equipment, boats, clothing and other items for exclusive use in one waterway.

If you are moving items between waterways you should always Check, Clean, Dry.

Check: Before leaving a waterway, check items for clumps of algae. Leave any debris that is found at the waterway.

Clean: Clean all items for at least one minute with one of the following:

• Hot (60°C) water
• 2% solution of bleach
  • A 2% solution is 200ml of product with water added to make ten litre
• 5% solution of salt
• 5% solution of dishwashing liquid
• 5% solution of antiseptic handcleaner
• 5% solution of nappy cleaner
  • A 5% solution is 500ml or 2 cups, with water added to make ten litres.

All these items can be found at your local supermarket. We recommend that you use products that are biodegradable.

Dry: If cleaning is not practical, dry the item to the touch and then leave drying for an additional 48 hours.

Specific cleaning methods have been developed for some freshwater activities.

About Didymo

Biosecurity NZ Didymo page