Biosecurity New Zealand and mana whenua for the Waikato River are urging people who work and play in and around the river to keep a lookout for a new-to-New Zealand clam species that has been found at Bob's Landing near Lake Karāpiro.

The freshwater gold clam (also known as the Asian clam, or by its scientific name Corbicula fluminea) is native to eastern Asia but is also widely established in North America, South America and Europe.

Overseas, these shellfish are a pest species because they reproduce rapidly and can clog up water infrastructure such as hydro-electricity plants, municipal water supply and irrigation systems.

They are also potentially a threat to native species, as in large populations they consume a lot of plankton.

Biosecurity New Zealand Deputy Director General Stuart Anderson says 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.

"We are partnering with Waikato-Tainui, the Waikato River Authority, the Waikato Regional Council, Te Papa Atawhai Department of Conservation and Toitū Te Whenua Land Information New Zealand to understand this incursion and how best to respond to it.

"This includes setting up a panel of technical and mātauranga experts to provide us with management advice.”

Initial checks have found the freshwater gold clam present over a 45-kilometre stretch of the Waikato River, from 1.5km upstream of Bob's Landing, just upstream of Lake Karāpiro, and downriver to Hamilton.

Stuart says the plan now is to search further, both within the Waikato River and in other rivers and lakes that are linked through human activity.

"This wider surveillance will include using targeted eDNA testing.

"To support this science, we're asking people who work around the river, or boat, fish or swim there, to keep a lookout and report any sightings of this new-to-New Zealand freshwater clam.

"They are a dirty white to yellow or tan and adult ones are 2-3 cm across. They can be found within the water, sitting on top of sandy or muddy surfaces, or buried shallowly within them. They're quite distinctive – there are no New Zealand species that look like this in the river."

Freshwater gold clams are not safe to eat from the Waikato River which is known to have high concentrations of toxins in the river. They filter-feed from the water and accumulate toxins in their gut.

Full information, which includes clear images of the clam, is on the Biosecurity New Zealand website at:

Suspected sightings can be reported to Biosecurity New Zealand on 0800 80 99 66 or by completing the online reporting form at report.mpi.govt.nz.

It is helpful to note the precise location and provide a close-up photo of the clam as well as one that shows the surroundings. Please do not disturb the organism.

Stuart says this situation is a reminder of the need to prevent the spread of invasive species like this clam between rivers and lakes and following Check Clean Dry guidance is the best approach.

Before moving boats or any watercraft, trailers and gear to another river or lake, or another part of a river or lake: remove any visible matter, including any clams or weed you can see and washdown gear and craft with tap water onto grass.

Full information is here