Hornwort Confirmed In Lake Okataina

Environment Bay of Plenty has confirmed that infestations of the aquatic pest plant Hornwort have been found in two bays at the south-western end of Lake Okataina. Delimitation work to assess the full extent of the incursion will be carried out from next week.

Hornwort (Ceratophyllum demersum) is one of the most invasive aquatic weeds as it is not as depth-limited as other invasive species. It can spread easily and rapidly displaces native vegetation in shallow and deep water.

Environment Bay of Plenty Group Manager Land Management Warwick Murray said this recent find was very disappointing.

“This really emphasises the need for boaties and anglers to check, clean and dry their equipment when moving between lakes to prevent incursions like this from happening.

“Okataina has long been a top spot for trout fishing and recreational boating,” Mr Murray said. “The establishment of Hornwort would make accessing areas of shoreline by boat and shore-based fishing difficult.”

Weed fragments were found by NIWA staff in March last year and said they were likely to have arrived on a vessel used in nearby hornwort-infested lakes.

Lake Okataina is one of only a handful of remaining Rotorua lakes with a low level of weed infestation.

Mr Murray said that advice had been received from and consultation had taken place with Te Arawa Lakes Trust, LINZ, NIWA, Eastern Region Fish and Game, and DOC on the incursion.

“The next steps depend on the results of survey work in the infested areas,“ Mr Murray said. “Once we know the extent of the infestation we will be better placed to assess the situation before making any decisions on control.”