Duck shooters, eel fishers asked to help stop weed spread

2 May 2022, 9:27 AM

Duck shooters and eel fishers are being asked to do their bit to stop the spread of an aquatic weed, hornwort, in Poutō’s precious lakes.

The Northland Regional Council says hornwort (Ceratophyllum demersum) was thought to have been eradicated from Poutō lakes but was discovered in the last two years in three lakes and associated ponds and wetlands there.

Councillor Jack Craw, who chairs the council’s Biosecurity and Biodiversity Working Party says the lakes where the weed is found are on public and private land and are used by duck shooters and possibly eel fishers.

Hornwort in a hand.A file shot of hornwort at Poutō’s Lake Egg.

With that in mind, the council is appealing to both groups to avoid moving from lake to lake without cleaning their gear, boats and nets first as hornwort is spread easily by tiny fragments transported by these. Even dogs can spread hornwort caught up in their fur or collars.

“Hornwort and other aquatic pest weeds are invariably spread by people and their activities,” Cr Craw says.

Hornwort is a problem because it can quickly grow to fill shallow lakes eventually causing the lake to ‘flip’ from a clear water to an algal dominated state.

“This poor water quality can cause ecological collapse where a lake no longer supports submerged plants affecting birds, fish and other life.”

Councillor Craw says Poutō has some of NZ’s best dune lakes, including lakes ranked ecologically outstanding with good water quality and limited impacts of pests so the spread of hornwort into these lakes could be devastating.

The regional council is working with DOC, landowners and mana whenua on a programme to eradicate hornwort from Poutō’s three affected lakes - Lake Tutaki (on conservation land) and Lake Karaka and Lake Egg (both on private land) - before it spreads to the other lakes.

“However, this will take time, so we are asking anyone visiting any waterbodies in the area to be extremely vigilant and also to report any hornwort or other weeds such as oxygen weed.”

Aquatic pests including pest weeds and fish, are found in other parts of the region including farm ponds and dams and to prevent the spread duck shooters are strongly encouraged to ‘Check, Clean and Dry’ their gear before moving between waterbodies.

More information about aquatic and other weeds is available online at