This freshwater mollusc (also known as Asian gold clam) was discovered along a stretch of the Waikato River in May 2023. Biosecurity New Zealand is working with iwi and other partners to decide future actions. Keep reading to find out more about the clam and how you can help to prevent it from infesting Otago’s waterways.

These clams reproduce rapidly and form large populations that can clog water-based infrastructure such as electric generation plants, irrigation systems, and water treatment plants. They are filter feeders that can potentially compete with native species for food. 

We do not yet know how this species will respond in New Zealand conditions. 

Overseas, this clam has proved difficult to control and eradication has never been achieved.

This freshwater mollusc (also known as Asian gold clam) was discovered along a stretch of the Waikato River in May 2023 and should not be eaten.

Why not? Freshwater gold clam (Corbicula fluminea) are small filter-feeding shellfish that eat deposits from the river or lake bed. Because of this, they accumulate toxins in their gut.

Biosecurity New Zealand is working with iwi and other partners to decide future actions. Keep reading to find out more about the clam and how you can help to prevent it from infesting Otago’s waterways.

The freshwater gold clam is native to eastern Asia and is widely established in North and South America and Europe.

Freshwater gold clams can be found within the water, sitting on top of sandy or muddy surfaces, or buried shallowly within them. You may see their shells partly exposed, or their syphons (their breathing tubes) sticking out from the sediment. They can also be found amongst debris, such as leaves, that may have settled on the riverbed. The adult clams are 2cm to 3cm in length and are typically dirty white, yellow, or tan. They have an obvious ribbed texture on the shell.

Freshwater gold clams are quite distinctive and easily identified, as there are no similar looking New Zealand species.

You must notify the Otago Regional Council or the Ministry for Primary Industries if you suspect the presence of this organism

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

• note the location
• take a photo (if possible)

You can then either:

• freephone the Otago Regional Council on 0800 474 082,
• freephone Biosecurity New Zealand on 0800 80 99 66, or
• complete the online reporting form at Biosecurity NZ

If you are using the online reporting form, you'll need to start by saying you are a member of the public, that you want to make a report about 'a marine or freshwater issue' and then select 'freshwater fish or crustacean' from the dropdown box that will appear. Then you will be taken through some further questions including contact information and asked to load your images.

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.

Note: The 'check, clean, dry' advice may be adjusted as further technical information becomes available. Refer to the manufacturer’s instructions for gear and any commercial treatments.