Adam Hartland | Golden Clam Invasion: A Growing Threat to New Zealand’s Water Security

Dale Husband Adam Hartland | Senior Scientist at Lincoln Agritech

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New Zealand’s freshwater ecosystems are facing a new and urgent biosecurity threat: the golden clam (Corbicula fluminea), an aggressive freshwater mollusc capable of overwhelming rivers, lakes, irrigation systems, and municipal water infrastructure. With its rapid reproductive cycle and ability to dominate waterways, the species poses a direct risk to the country’s water security, hydroelectric operations, biodiversity, and primary industries.

The golden clam is a small bivalve, native to Asia, now infamous worldwide as one of the most damaging freshwater invasive species. It has established widespread populations in South America, the United States, and Europe, often causing millions of dollars in damage to water treatment plants and irrigation networks.

Its arrival in New Zealand – first detected in the Waikato River system – has raised alarm bells across government agencies, iwi, local authorities, and environmental scientists.

• A single clam can produce tens of thousands of offspring each year.

• Entire riverbeds can become blanketed in dense layers of clams within months.

Golden clams clog:

• Hydroelectric intake pipes

• Irrigation channels

• Municipal drinking water systems

• Cooling systems for industrial plants

In countries where infestations are established, mechanical clearing can cost millions annually.

The clams filter-feed aggressively, stripping nutrients and plankton from water systems. This:

• Outcompetes native fish and invertebrates

• Alters food webs

• Reduces biodiversity in affected rivers and lakes

New Zealand’s native freshwater species;  already under pressure;  could face substantial declines.

Clogged pipes and reduced flow levels increase the cost and complexity of providing safe drinking water. Some overseas cities have had to redesign entire water systems after golden clam invasions.

Biosecurity officials believe the most likely pathway was human-mediated transport, either through:

• Contaminated freshwater equipment (kayaks, boats, fishing gear)

• Illegal aquarium releases

• Ballast water or sediment movements

Once established, clams spread rapidly downstream and between catchments via water flow, birds, and human movement.

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