An invasive clam has been discovered in the Waikato River, the first time it has been found in New Zealand.
The Gold clam, also known as the Asian clam (Corbicula fluminea) can clog water-based infrastructure like electric generation plants, irrigation systems, and water treatment plants, the Ministry for Primary Industries (MPI) said.
It also poses a potential threat to native species because the clams can consume large amounts of plankton
They are prolific breeders, and one clam can produce 400 offspring a day and up to 70,000 a year, the ministry said.
Boaties in the Waikato were reminded to be strict about 'check, clean, dry' rules, to avoid spreading the clam or any other species, on surfaces of their boat or any other gear.
The clams were found by ecologists at Bob's Landing near Lake Karāpiro and after more investigation were found along about 50km of the Waikato River, from 1.5km upstream of Bob's Landing, and downriver to Hamilton.
Gold clam had been difficult to control overseas and there was no documented successful eradication.
Biosecurity New Zealand Deputy Director General Stuart Anderson said it was yet to be seen how the species would behave in New Zealand conditions.
Also not yet known was how they arrived in New Zealand, and a search was planned to see how far they had spread, including checking other rivers and using targeted eDNA testing.
"We are partnering with Waikato-Tainui, the Waikato River Authority, the Waikato Regional Council, Te Papa Atawhai Department of Conservation and Toitū Te Whenua Land Information New Zealand to understand this incursion and how best to respond to it," Anderson said.
"This includes setting up a panel of technical and mātauranga experts to provide us with management advice".
Anyone who spotted the clam was asked to report it to to Biosecurity on 0800 80 99 66, with details of location, and if possible a photo.
The adult clams are usually between 2 and 3cm long, have a ribbed shell and are dirty white, yellow, or tan.
MPI said the species was known to live in both freshwater and brackish water water and in a range of different temperatures and levels of saltiness. It could live in or on sandy or muddy areas as well as underwater.
"You may see their shells partly exposed, or their syphons (their breathing tubes) sticking out from the sediment," the agency said.
"They can be found within the water, sitting on top of sandy or muddy surfaces, or buried shallowly within them, and they can also be found amongst debris, such as leaves, that may have settled on the riverbed."
At Bob's Landing small shellfish and larvae were found attached to rocks.