How the war on gold clams was lost

Saturday, 22 March 2025

Gold clams are very easy to find on the banks of Lake Karāpiro.

The war to eradicate invasive gold clams, first discovered in the Waikato River in May 2023, has been lost with officials turning to a long-term management plan to contain their spread.

Freshwater gold clams now join koi carp, gambusia (mosquito fish), catfish, rudd, and alligator weed as unwanted residents of the country’s largest waterway.

However, the move has left the Waikato River Authority and the Tūwharetoa Māori Trust Board disappointed nothing more could be done.

A biosecurity notice for the invasive freshwater gold clam at Lake Karāpiro where they were first found at Bob’s Landing in May 2023.

In his “final update on the response, news on activity to prevent the spread, and the progression to long-term management of freshwater clams”, Biosecurity New Zealand (BNZ) pest management director John Walsh said a long-term plan for freshwater clams had been put in place.

Walsh said around $2m has been spent on the response since mid-2023, and their presence has been confirmed along a stretch of approximately 200km of the Waikato River, extending from Lake Maraetai at Mangakino to Port Waikato.

He said the plan would focus on containing clams to their current known locations in the Waikato catchment area, reduce their impact where feasible, and develop tools to achieve this.

Gold clams were first found in the Waikato River in May 2023. Officials believe they were in the river for at least two years before being discovered.

A national surveillance strategy, and a rapid assessment plan for new incursions will be developed, with regional councils and the Department of Conservation (DOC) leading the operational delivery of the plan, in partnership with iwi.

“The involvement of iwi, regional councils, river and lake users, and other agencies has been critical throughout the response phase, and will continue to be key in helping stop the spread in the long-term,” Walsh said.

Deep Dive Division managing director Tua Karalus said there were ‘heaps’ of gold clams in cars they dragged from the Waikato River this week.

BNZ’s Freshwater Biosecurity Partnership Programme will now work to “understand and manage regional and national pathways through which significant freshwater pests are spread”.

“Its focus is to increase knowledge, share expertise, develop best practice for management, and support the Check Clean Dry campaign and other freshwater biosecurity operations around the country,” Walsh said.

“Key recommendations in the plan include a substantial increase in the number of eDNA samples collected … and the use of visual sampling techniques, such as dredge tows.

“Early detection allows for timely management and intervention processes, significantly increasing the chances of successful containment.”

Tūwharetoa Māori Trust Board chief executive Rakeipoho Taiaroa said containment would only lead to a loss of biodiversity.

Walsh said treatment to eliminate gold clams from from the Taupō Aqua Park lagoon began earlier this month.

“There has been a positive response with many dead clams surfacing following application of the treatment.”

Tūwharetoa Māori Trust Board chief executive Rakeipoho Taiaroa said containment strategies only risked future incursions, and would continue to harm the river’s biodiversity.

“Biosecurity NZ will be aware there is statutory direction in our Upper Waikato River Settlement Act to restore and protect the health and wellbeing of the Waikato River for present and future generations.”

He said if the eradication of clams in the aqua park was achievable, then it should be done.

‘Didymo’ Dave Cade said he did not think eradication would be possible, and education and awareness was critical to stop the spread of gold clams.

“We are still very concerned about the high potential for clams to spread to other waterways, and see a collaborative effort by relevant agencies and entities is needed to support containment efforts.”

Taiaroa said containment was basically the bare minimum.

Walsh said the importance of public awareness was highlighted by a recent survey of river users at boat ramps along the river.

Lake Taupo Aqua Park was closed after gold clams were found in its lagoon.

Of the 361 people surveyed, 42% were not aware gold clams had been found in the Waikato River, and 62% had not heard about Check Clean Dry.

Walsh said a number of projects were underway to help prevent its spread.

At Lake Karāpiro, ballast-tank treatment trials, held with the New Zealand Water Ski Racing Association, have been successful, and BNZ is looking for a suitable Waikato-based service provider to continue that work.

A team of ambassadors had been active at events such as the Waka Ama Nationals and the Maadi Regatta, making sure everyone was aware of Check Clean Dry requirements

Taupō-based biosecurity campaigner “Didymo” Dave Cade was pragmatic about the new management plan saying, as always, “the biggest threat is people”.

“I never saw eradication as an option, because how would you do it if it was a microscopic organism?

“These things are so small when they are born they are hard to detect with the naked eye … I don’t think elimination was ever a serious option.

“But, as they are saying, awareness and containment is the key.”

Waikato River Authority co-chairperson Danny Loughlin said the decision not to eradicate was “disappointing”.

“We shouldn’t give up on places where eradication could be successful,” he said.

Deep Dive Divison managing director Tua Karalus said there were “heaps” of gold clams in car wrecks his team pulled out of the Waikato River recently.

“It’s the perfect spot for them.

“We’ve known about this threat for some time … I just hate the lack of urgency when we have these incursions.

“Why are we not upping the ante in terms of our biosecurity and doing more to protect our rivers and waterways?”