An new invasive shellfish, the Gold clam or Asian clam (Corbicula fluminea), has prompted pleas from the country's regional councils for boaties and water users to be vigilant, after its discovery in the Waikato River in May 2023.

The eastern Asian pest which lives in fresh water, consumes large amounts of plankton and has the ability to produce up to 70,000 offspring annually per clam.

This makes it a threat to not only New Zealand's native water species, but also a potential clog to water-based infrastructure like irrigation systems, treatment plants and hydro systems.

Since its discovery, Biosecurity New Zealand has been conducting surveillance in the wider Waikato region and a targeted selection of lakes and rivers around the country.

To date, clams have only been found along a 45-kilometre stretch of Waikato River, from the Lake Karāpiro area to Hamilton.

Testing for environmental DNA (eDNA) returned positive results on some water samples from Waikato River outside this area, but they are early results that need validating.

Gold or Asian Clam. Photo: USGS

It is not yet known how this pest arrived in the country.

Environment Southland (ES) biosecurity and biodiversity manager Ali Meade currently doesn't have enough information to understand the implications of the gold clam on Southland’s habitats, species, structures and hydro power stations.

"[But] given how easily freshwater pests can move, we are concerned about it reaching Southland waters," Meade said.

"We encourage all water users to follow the Clean, Check and Dry process, particularly if moving things such as fishing gear, kayaks, boats etc between islands."

Where to look out for this pest

Freshwater gold clams are found in freshwater or brackish water (near river mouths), sitting on top of sandy or muddy surfaces, or buried shallowly within them.

They can also be found among debris, such as leaves, that may have settled on the riverbed.

If you think you've seen the freshwater gold clam:

Freephone Biosecurity New Zealand on 0800 80 99 66, complete the online reporting form at Biosecurity NZ, or contact ORC’s Biosecurity team: [email protected]

Help stop the spread – Check, Clean, Dry

If you fish, swim, boat or row, follow the Check, Clean, Dry guidelines to help stop the spread of this clam to other rivers and lakes through New Zealand.

Before moving to another location at the river, or to another river or lake:

Check

Remove anything visible including clams, weed, or mud. Drain all water.

Clean

Wash down your gear and craft with tap-water onto grass beside the river or lake, or at home – not into a stormwater drain system. This will flush off clams that can be too small to be seen.

For gear made of absorbent materials (for example clothing, wetsuit), which will stay wet longer, you should do a hot wash (above 45 degrees) or pop it in a freezer until solid.

Dry

Allow gear to dry to touch, inside and out, and then leave it to dry for at least 5 days before going back in a river or lake.

Dry areas inside the watercraft where water has pooled, for example with an old towel, and then leave the craft to dry for at least five days.

The hull of a watercraft will dry when towed.