Record funding boost for Lake Karāpiro weed control

A record level of partner funding will support aquatic weed control at Lake Karāpiro this summer, helping keep key areas of the lake accessible and enjoyable for the thousands of people who use it for recreation and sport.

A total of $290,000 is available for the 2026/27 lakeweed control programme, compared with $159,000 last year.

The increased investment has been made possible through greater contributions from Waikato Regional Council, Mercury, Waipā District Council and Toitū Te Whenua Land Information New Zealand (LINZ), alongside funding from Karāpiro Rowing Incorporated.

More funding, more weed control

The additional funding means substantially more of the lake can be targeted through the spraying programme this season.

During last year’s pre-Christmas programme, around eight hectares were treated using boat-based spraying. This season, subject to suitable weather and lake conditions, approximately 150 hectares are planned for treatment before Christmas, including around 130 hectares using helicopter-based spraying and a further 20 hectares by boat.

That is nearly 19 times the area treated during the same period last year.

Boffa Miskell leads the operational delivery of the weed control programme. 

Ahead of spraying, Boffa Miskell will undertake a survey in November to map the current distribution and density of weed across the lake. This will help determine where treatment will be most effective.

Treatment areas will include Mighty River Domain, Waipuke Park, Keeley's Reserve, Moana Roa Reserve, Hora Hora Domain and Little Waipā Reserve.

Why it matters

LINZ Leader Biosecurity Tracey Burton:

“Lake Karāpiro is a really important place for the community and for the many people who swim, paddle, row, boat and spend time on the lake.

“Our investment is about looking after that experience, but also about the wider biosecurity picture. Managing aquatic weeds and other freshwater pests here helps reduce their impact on lake users and, importantly, helps prevent them being spread from Lake Karāpiro into other lakes and waterways.

“That’s why it’s great to see the organisations and communities connected to the lake working together and investing in its ongoing management.”

Waikato Regional Council Chairperson Warren Maher:

“Our council is pleased to support efforts to expand hornwort control at Lake Karāpiro. This investment will help protect a nationally significant waterbody that delivers substantial environmental, recreational and economic benefits to the Waikato region, including hosting major events that contribute millions of dollars to the local economy each year.”

Mercury Head of Operations, Generation, Emily Collis:

“Controlling invasive aquatic weeds helps protect lake ecosystems, supports recreational use of the water and safeguards hydrogeneration on the Waikato River.

“Effective lake weed management relies on strong partnerships, and we’re pleased to be working with community groups and government agencies to expand control efforts at Lake Karāpiro.

“Alongside this work, we’ll continue our summer lake weed control programme at four other hydro lakes where we operate hydro stations on the river.”

Waipā District Mayor Mike Pettit:

"We are greatly appreciative for the support to date to tackle the very real problem of Hornwort and its negative impact on Lake Karapiro. We will continue to seek further funding over the coming months before moving into the next important phase, working with others to develop a robust strategic plan to deal with the issue moving forward."

Karāpiro Rowing Incorporated Chairperson Lachie Spence:

“This funding will be crucial to ensuring our volunteers can deliver another great season of rowing events without the threat of weed for rowing, and for other lake users.”

Rowing New Zealand Chief Executive Simon Wickham:

“We are delighted to see stakeholders recognising the valuable social, environmental and economic value a lake with less weed can provide for us all and we're grateful to all that have funded the spray program. In doing so they demonstrate support for the value this awa, Lake Karāpiro, provides for all and their kaitiakitanga is deeply valued by our rowing community alongside all other lake users.”

Managing an ongoing challenge

Hornwort is one of the key aquatic weeds managed at Lake Karāpiro. It can grow into large, dense beds that interfere with swimming, boating, rowing and access to the water.

It is particularly challenging to manage because it is mobile. Large mats can break away and move around the lake with water currents, meaning areas that have previously been treated can be affected again by hornwort moving in from elsewhere.

This means weed control at Lake Karāpiro is not a one-off job and needs to respond to changing conditions across the lake.

Success at Lake Karāpiro is about managing the impact of the weed rather than expecting to eliminate it entirely.

Having more funding available gives the programme greater ability to respond to conditions on the lake and focus control where it can make the biggest difference.

Lake Karāpiro aquatic weed control programme

The lakeweed control programme has been in place since 2007 and is coordinated by LINZ, working with Waipā District Council, Waikato Regional Council, Mercury Energy, mana whenua, Auckland Waikato Fish & Game, and Boffa Miskell.

Read more about upcoming control work: Biosecurity control work | Toitū Te Whenua - Land Information New Zealand