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'Full didymo mode' needed for gold clam invasion says Stu Muir, chair and farmer on Waikato River

Updated: Aug 14, 2023

Invasive gold clams could be a "massive problem" for the Waikato awa, and other lakes and rivers are also at risk says Endangered Species Foundation chair, Stu Muir.

Muir, who farms along the Waikato River, said on of the issues with the clam was its "phenomenal" reproductive rate. He said, one clam alone can produce 400 offspring in a single day, and as many as 70,000 per year.

"At this stage, based on what we've seen overseas, it could be a massive problem," Muir said.

Gold clam different sizes - Photo: NIWA

What’s happening?

The invasive Gold clam (also known as Asian clam) has been discovered in the Waikato River, for the first time. The clams were found near Lake Karāpiro and along approximately 50km of the Waikato River. At Bob's Landing small shellfish and larvae were found attached to rocks. Controlling the Gold clam has been challenging in other countries, and successful eradication has not been documented. DOC, Waikato-Tainui, the Waikato River Authority, the Waikato Regional Council, Te Papa Atawhai Department of Conservation and Toitū Te Whenua Land Information New Zealand are collaborating on how best to respond[1].

Gold clam - Photo: NIWA

Key facts

  • The gold clam is an invasive species that can clog water-based infrastructure.

  • It can consume large amounts of plankton, posing a threat to native species.

  • A single gold clam can produce 400 offspring per day and up to 70,000 per year, making them prolific breeders.

  • It has a ribbed shell, which is typically dirty white, yellow, or tan. It can be found in freshwater and brackish water, on sandy or muddy surfaces, and among debris on the riverbed. Adult clams are between 2 and 3cm long

  • They are hermaphrodites, with male and female reproductive organs and can self-fertilise

  • Asian clams can contribute to a variety of problems in waterways including the excretion of significant amounts of inorganic nutrients, particularly nitrogen, which promotes the growth of algae and contributes to pollution. The spread of these clams can have serious consequences for our waterways[2].

  • In the US, a higher abundance of Asian clams has been associated with lower growth of native mussels[3]

  • There are fears for the survival of our native freshwater muscles Kākahi (also as kāeo and torewai) in the Waikato awa

  • The clam may also negatively impact other taonga species like the tuna, longfin eel which is classified as an endangered species

What can you do?

Help stop the spread

Boat owners - follow the "check, clean, dry" rules to prevent the spread of the clam or any other species on their boats or equipment.


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


Do a washdown of your gear and watercraft with tap-water onto grass, beside the waterway or at home and not into a stormwater drain system. This will flush off clam larvae, which can be too small to be seen. For gear made of absorbent materials, which will stay wet longer, apply a cleaning treatment.


Allow gear to dry to touch, inside and out, then leave it to dry for at least 5 days. 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.

Report sightings

You may see their shells partly exposed, or their syphons (breathing tubes) sticking out from the sediment. Report sightings with location and photos to MPI 24 hour emergency hotline 0800 80 99 66.

About Stu Muir

With a genuine passion and enthusiasm for saving NZ's most vulnerable indigenous species and habitats, Stu Muir has a well-respected background in ecological restoration, focused towards wetland and coastal conservation. With a Bachelor of Arts in Education and History from Otago University, Stuart is conversant in Te Reo.

​Stuart has a proven background collaborating closely with key national and regional stakeholders, including Iwi, NIWA, DOC, Fish & Game, Forest & Bird, Predator Free NZ, Dairy NZ and district councils. Focused on developing sustainable conservation-based projects and initiatives, Stuart acts as an educator and adviser to school and university groups, seeking to improve their environmental and conservation impact and participation.

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