Waikato River at risk from freshwater clam invasion

Friday, 26 May 2023

At least six sites on the Waikato River have been found to harbour freshwater gold clams, an invasive species that can destroy habitats, clog water supplies, and damage hydroelectric dams.

The discovery of an invasive clam species in the Waikato awa has “mortified” kaitiaki, who fear it could further disrupt the river’s already fragile ecosystems.

On Thursday morning, the Ministry for Primary Industries (MPI) announced the discovery of freshwater gold clams, (also known as the Asian clam) in the Waikato River near Lake Karāpiro.

The invasive freshwater clam has the potential to destroy native habitats, clog water supplies and hydroelectric dams, and could infest Lake Taupō if not properly contained.

Freshwater gold clams have been found at six locations along the Waikato River.

The clams have also been detected at Horahora Domain, Moana Roa Reserve, Keeley Reserve, Cambridge Boat Ramp, and at Wellington Beach in Hamilton.

Their discovery was a “huge disappointment and will likely draw a strong reaction from marae along the length and breadth of our tupuna awa”, said Waikato-Tainui chairperson Tukoroirangi Morgan.

“To say I am mortified is an understatement, more needs to be done to protect our fragile ecosystem against all introduced pests that find themselves in our waterways,” he said.

Waikato-Tainui chairperson Tukoroirangi Morgan said the iwi was at its wits’ end with the clam discovery following toxic algae at Whangamarino wetlands.

According to a Biosecurity New Zealand (BNZ) report, both live and dead clams were found by investigators on May 5, “indicating an established breeding population”.

MPI officials have no idea where the clams came from, but if they take hold they are almost impossible to eradicate, BNZ deputy director general Stuart Anderson said.

“It is not known how the freshwater gold clam will behave in New Zealand conditions, but overseas it has proved difficult to control and there has been no documented successful eradication,” he said.

The clams are a dirty white to yellow or tan colour, grow up to two to three centimetres across, and can be found in water, sitting on top of sandy or muddy surfaces, or buried shallowly within them.

Anderson said it was not safe to eat clams from the Waikato River, which was known to have high concentrations of toxins.

Freshwater gold clams have been found in the Waikato River and could cause serious problems if left unchecked.

Morgan said Waikato-Tainui would be pushing for help from central Government to eradicate, or at least control, the spread of the highly invasive species.

“We have recently worked with mana whenua to place a rahui on the Whangamarino wetlands because rising toxicity associated with algae growth and now combined with this latest issue, we are simply at our wits’ end,” Morgan said.

“When Lady Raiha and I negotiated the river settlement, the health and well-being and ongoing maintenance of our tupuna awa was one of our main priorities hence the establishment of the Waikato River Authority.”

The Waikato River Authority did not respond to requests for comment, but Waikato Regional Council chief executive Chris McLay said the discovery was “hugely disappointing”.

“It’s been found over an especially popular stretch of the river,” he said.

“Lake Karāpiro alone has 50 days of events every year that attract thousands of competitors, and through summer our maritime officers can find hundreds of boats, jet skis and kayaks using the lake on any given day.

“It’s possibly one of the most busy and congested stretches of inland water in New Zealand.

“To protect our precious waterways – not just here in the Waikato region, but right around New Zealand – we strongly urge water users to make sure they’re following the ‘Check Clean Dry’ approach.

“It will be vital to stopping the spread of this species elsewhere,” McLay said.

A Ngāti Tūwharetoa communications spokesperson said the iwi, who are the guardians of Lake Taupō, would be discussing an appropriate response to the situation over the coming weeks.

Suspected sightings should be reported to Biosecurity New Zealand on 0800 80 99 66 or online at report.mpi.govt.nz.

People are being asked to note the precise location and provide a close-up photo of the clam as well as its surroundings.

River users are being encouraged to:

Check: Remove any visible matter, including any clams you can see, along with plant material or mud. Drain all river water.

Clean: Wash their gear and watercraft with tap-water onto grass, beside the waterway or at home and not into a storm water drain system. This will flush off clam larvae, which can be too small to be seen.

Dry: Allow gear to dry, inside and out, then leave it to dry for at least five days. Dry areas inside the watercraft where water has pooled, and then leave the craft to dry for at least five days.