Work to manage invasive lake weed hornwort begins at Lake Karāpiro

Work to manage the invasive lake weed hornwort will begin at Lake Karāpiro next week.

The control work is part of Toitū Te Whenua Land Information New Zealand’s (LINZ) annual biosecurity programme.

LINZ Leader Biosecurity Tracey Burton says Boffa Miskell will be using both a boat and a helicopter to spray weed near boat ramps, ski lanes, and popular swimming spots over the coming weeks, weather permitting. This follows control work undertaken earlier in the summer.

“This summer we’ve seen ideal conditions for hornwort growth, and we’ve heard from the community about the impact it’s having on their enjoyment of the lake,” says Burton.

Hornwort is one of New Zealand’s most problematic invasive lake weeds. First recorded in Napier in 1961, it has since spread across much of the North Island through human activity. It forms dense floating mats that can take over lakes, choke waterways, smother native aquatic plants, and impact swimming, fishing, rowing, and boating.

Burton says lake users can help prevent the spread of aquatic weeds and pests by checking, cleaning, and drying all water gear and craft.

“This is especially important to prevent not just the spread of hornwort but also the highly invasive freshwater clam from Lake Karāpiro to other nearby water bodies, including the Rotorua Te Arawa lakes,” she says.

“Baby clams are invisible to the naked eye and can easily hitch a ride on items like wetsuits, jet skis, fishing gear, and boats. Once established, they reproduce rapidly, forming dense beds in the sediment outcompeting our native kākahi (freshwater mussels).

The control work at Lake Karāpiro is jointly funded by LINZ, Mercury Energy, Waikato Regional Council and Waipā District Council.

For exact dates of control work, including any recommended stand‑down periods, view Current and upcoming control work.