Battle against hornwort paying off on Lake Ōkataina

Two weed cordons were originally erected on Lake Ōkataina to help contain hornwort. Photo / File

The removal of a weed cordon on Lake Ōkataina represents a significant step in eradicating one of New Zealand's worst freshwater weeds from the lake.

Bay of Plenty Regional Council is celebrating the removal of the weed cordon, that kept boats out of the Motuwhetero arm of the lake, last week.

Two weed cordons were originally erected to help contain hornwort which can grow taller than a three-storey building (10m).

Senior Projects Officer Hamish Lass said hornwort was first discovered in the lake in 2010.

Example of a weed cordon in operation. Photo / Supplied

"Since then we have invested a great deal of time and resources to contain the hornwort using a combination of herbicide and hand removal.

"The use of the weed cordon at the southern end of the lake, which excluded boats from the area while it was being treated, has been instrumental in containing the spread.

"The fact that we are now in a position to remove it represents a significant step in eradicating hortwort completely from the lake," he said.

Hornwort bloom at Lake Rotoehu. Photo / Supplied

Once hornwort enters a waterway it can very quickly form dense weed beds that smother all other freshwater plants. It can block waterways and impact on boating, fishing and other lake uses.

New hornwort plants can form from even tiny pieces of the easily broken stems and cause new infestations when those fragments are carried to other waterways by outflows, birds, fishing equipment or boat movements.

Hornwort weed bed. Photo / Supplied

To stop the spread of freshwater pests, Lass reminded all lake users to check, clean and (when practical) dry their boat, trailer, prop, fishing and sporting equipment when moving from one waterway to another.

The second weed cordon at the Lake Ōkataina boat ramp will remain in place to further protect the lake from potential new weed infestations.