Otago Regional Council (ORC) is asking for help to keep an overseas interloper from local waters after the discovery of a new aquatic pest species in the North Island.

Discovered along a stretch of the Waikato River in May this year, the freshwater gold clam (Corbicula fluminea) poses a new threat to New Zealand waterways, native freshwater species and infrastructure. 

ORC’s biosecurity team has concerns the fast-spreading pest could hitch a ride from northern lakes and rivers to Otago’s lakes and waterways, ORC environmental implementation manager Libby Caldwell said.

“Our worry is that people transporting recreational equipment such as boats and trailers, fishing gear, paddleboards, kayaks, or jet skis between the North and South Islands may inadvertently bring this new pest to Otago. 

“That’s why we’re getting the word out now in the hope we can prevent a new aquatic pest from invading our lakes and rivers.” 

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

The freshwater gold clam can clog water-based infrastructure such as electric generation plants, irrigation systems, and water treatment plants. PHOTO: Supplied

Freshwater gold clams can spread when they attach to boats or are carried in ballast water, used as bait, through the aquarium trade or carried further afield by water currents.

“It’s best practice to get in the habit of thoroughly washing down any recreational freshwater equipment, away from lakes and rivers,” Libby said. “This method also takes care of a variety of other pests, like lagarosiphon and didymo.” 

If people think they have found freshwater gold clams, Libby asked that they take a photo and report the location to the ORC or Biosecurity New Zealand.

The freshwater gold clam is native to eastern Asia and is widely established in North and South America and Europe. They can reproduce rapidly and form large populations which can clog water-based infrastructure such as electric generation plants, irrigation systems, and water treatment plants.

They are filter feeders and can potentially compete with native species for food.

Juveniles will spread passively in the water column. In rivers, colonisation downstream is easily achieved as juveniles are transported by currents, or through being attached to floating vegetation.

It is not yet known how this species will respond to New Zealand conditions, but research indicates that the freshwater gold clam has a thermal tolerance of down to two degrees Celsius, which means that most of Otago is potentially occupiable for this species.

If there is an incursion of this pest species into the Otago freshwater system, there are likely to be significant environmental and economic impacts.

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, such as clothing or wetsuits, you should do a hot wash (above 45 degrees) or pop items in a freezer until solid; and dry: Allow gear to dry to touch, inside and out, and then leave it to dry for at least five 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.