The invasive freshwater clam is quite distinctive and easily identifiable as there are no similar looking New Zealand species. 

An adult clam measures 2-3cm long, is typically dirty white, yellow, or tan in colour, and has an obvious ribbed texture on the outside of the shell. 

It is found in freshwater and estuaries or brackish waters, often buried in large clumps. You may see its shells partly exposed, or syphons (breathing tubes) sticking out from the sediment. 

The invasive freshwater clam can also be found amongst debris, such as leaves, that may have settled on the riverbed. It can survive a wide range of water conditions, including temperature and saltiness. 

The invasive freshwater clam is native to Eastern Asia and is widely established in North and South America and Europe where it has become a pest. 

It is a highly invasive pest that reproduces rapidly – up to 400 juveniles a day and up to 70,000 a year.  

This pest is a filter feeder that can potentially compete with native species for food and negatively impact the health of our precious lakes. 

It can clog water-based infrastructure, such as electric generation plants, irrigation systems, and water treatment plants. 

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

You can help stop the spread of this pest by following the Check, Clean, Dry method below. 

When you move from one part of the river to another, or from one river or lake to another: 

Check 

• Remove any plant matter, mud or visible weed or clams from your gear and leave it at the river or lake bank, or put it in the rubbish. Drain all river or lake water from your boat, ballast tanks and gear. 

Clean 

• Blast your gear and craft with tap water onto grass, not into a stormwater system or drain.
• For absorbent materials, use one of the following treatments:
  • Soak in hot tap water (50°C to 55°C) for at least 5 minutes, or
  • Soak in 5% bleach solution (5 litre mix = 250ml bleach in 4.75 litres water) for an hour, or
  • Freeze till solid (overnight), or
  • Soak in salt solution at 100ppt (parts per thousand) (5 litre mix = 500g salt in 5 litres warm water) for 4 hours.

Get a full list of approved treatments, including options for situations where none of the above is suitable, from mpi.govt.nz - Treatment options

Dry 

Dry areas inside watercraft where water has pooled, then leave the craft to dry for at least 48 hours (2 days).

Allow gear to dry to touch, inside and out, then leave it to dry for at least 48 hours (2 days) before using again. 

More information can be found on the MPI website at: mpi.govt.nz