Biosecurity New Zealand has confirmed the presence of invasive freshwater gold clam in the Ruakohua stream tributary near the New Zealand Steel Glenbrook site in south Auckland.
The detection is considered linked to the existing Waikato River incursion, as two consented water takes connect the Glenbrook steel mill with the lower Waikato River. As the Glenbrook site is connected to the Waikato River system, Biosecurity New Zealand does not consider this a separate incursion.
The Glenbrook detection is, however, the first confirmed presence of the invasive freshwater clam in the Auckland region.
Auckland Council, mana whenua and New Zealand Steel are working together to determine the extent of the clam's presence at the site and assess any risk of further spread, with support from Biosecurity New Zealand and Waikato Regional Council.
Auckland Council General Manager Environmental Services Samantha Hill says the detection reinforces the importance of preventing the movement of freshwater pests between waterways, and the council’s ongoing surveillance programme.
"While this detection is connected to the existing Waikato River incursion, it's still disappointing to see invasive freshwater gold clam confirmed in the Auckland region. Once freshwater pests become established, they are extremely difficult to remove, which is why preventing their spread remains our best defence,” says Ms Hill.
About the invasive freshwater clam
Invasive freshwater clam (Corbicula) was discovered in the Waikato River in 2023. These clams can spread quickly, with each clam able to have up to 70,000 juveniles each year.
Their microscopic young are tough invaders which can easily attach to and travel on wetsuits, kayaks and other gear unless the gear is completely dried out and treated.
We know from overseas examples that the invasive freshwater gold clam is a significant threat to our native ecosystems, and that they can clog up infrastructure like power generation systems, water treatment plants and irrigation systems.
How you can help stop the spread of freshwater clams
To prevent the spread of freshwater clam, water users need to follow the evidence-based biosecurity protocol 'Check Clean Dry' for all watercraft and gear when moving between waterways. Follow this 'Check Clean Dry' guide for all North Island lake and river users.
When visiting the Waikato and the Bay of Plenty, it is important to be familiar with the Controlled Area Notices (CANs) that are in place for the Waikato River and Te Arawa Lakes, including Lake Ōkataina. The CANs have specific requirements for each area.
To find out more visit: www.mpi.govt.nz/clamrules
These rules are in place because any movement of craft, equipment, and gear between waterways poses a risk of spreading the freshwater clam to areas that are not infested.
If you think you have found invasive freshwater clams
Keep an eye out for Corbicula and report suspected sightings to Biosecurity New Zealand. Please do not move it, but instead take a photo, if possible, and note the location. Then either:
• freephone 0800 809 966
• or complete the online form at report.mpi.govt.nz
Biosecurity New Zealand’s national surveillance programme
The detection at Glenbrook came after extensive surveillance undertaken earlier this year as part of Biosecurity New Zealand's national Corbicula surveillance programme. Key Auckland freshwater sites were surveyed with no evidence of freshwater gold clam found in samples from elsewhere in the Auckland region.
Across the country, approximately 65 water bodies were surveyed to detect signs of the invasive clam and three other invasive mussels (Zebra, Quagga and Golden) not yet present in New Zealand.
The sampling was undertaken by mana whenua, the Department of Conservation, regional councils and Watercare using the plankton net surveillance method. It did not uncover any new detections of the clam.
Surveillance will continue in Auckland and other high-priority locations throughout Aotearoa New Zealand to help detect any further spread and inform ongoing management activities.
Taking precautions while moving between waterways is key to limiting the spread of Corbicula – all users should Check Clean Dry their gear when moving between waterways.