Councillors have argued South Island regional councils should lobby Biosecurity Minister Andrew Hoggard for funding to be set aside to keep the pests out of the mainland.
Council environmental implementation manager Libby Caldwell said work was already under way regionally and nationally to raise awareness of the two exotic freshwater gold clam species, Corbicula fluminea and Corbicula australis, and the potential threat the bivalves posed.
"Importantly to date, surveillance work has been undertaken and there is no detection of Corbicula outside of the Waikato River and Lake Taupo Aqua Park," Mrs Caldwell said.
"But there are concerns that the species could spread — and it has been determined that eradication is not feasible in the Waikato River with the current tools available, and the focus is on suppression and preventing the spread," Mrs Caldwell said.
Council staff were working with Biosecurity New Zealand and others on the issue at present, she said.
In a report to the council’s environmental implementation committee, staff said the pest species could spread quickly in rivers using water flows and were easily transported to new waterways through human activity.
"They can outcompete and displace native and taoka species, compromise water quality, clog and damage water infrastructure, such as hydro-electricity and municipal water, and impact tourism and recreational values.
"The potential environmental and economic impacts to Otago’s lakes and rivers could be significant."
Both species could produce 400 juveniles per day and up to 70,000 juveniles per year and the clams were known as "one of the most prolific freshwater invaders worldwide", the report said.
Locally, freshwater mussels could be at risk, and the clams could exacerbate water quality issues.
About $100,000 had been spent to date in the Waikato to prevent issues at the Waikato Water Treatment Plant since the pest was first detected in the river last year.
However, council staff and staff from other councils and agencies viewed Cook Strait as "a defensible boundary", the report said.
Cr Kate Wilson said an incursion in the South could be a "horror story".
Cr Gary Kelliher called on his colleagues to recommend chairwoman Cr Gretchen Robertson work with other South Island regional councils to write to the minister "emphasising the high level of concern" at the risk of gold clams spreading to the South Island and urging him "to ensure adequate funding is in place for containment measures and introducing appropriate requirements for all waterborne items to be suitably cleaned prior to departing the North Island".
"As a council we’re battling wallabies that have arrived here and huge sums of money are having to go into dealing to that in relatively small numbers.
"Here’s an opportunity where it’s very challenging to have it in the North Island.
"We have a barrier, and it’s just about working together with other regional councils across the South Island to best avoid this arriving here," Cr Kelliher said.
"It will have grave implications for a whole heap of activities in the South Island.
"It’s obviously creating issues already in the North Island and New Zealand is a small place.
"Any emphasis we can make now, any assistance we can request, and in a collective manner with the South Island, to me, is super urgent and needs to be under way asap."
The committee unanimously supported Cr Kelliher’s motion.
Mr Hoggard has been approached for comment.
