Source: Radio New Zealand
Eradicating the gold clams could cost up to $1.3 million, with no guarantee of success. File photo. NIWA
Boating restrictions at Lake Rotomanu in New Plymouth are to remain while Taranaki Regional Council seeks partners to help fund an attempt to eradicate the invasive gold clam.
Tuesday’s full council meeting weighed up a report by environment services manager Steve Ellis that outlined five options for the management of freshwater gold clams (Corbicula fluminea) in Lake Rotomanu.
Councillors heard attempting to eradicate the clams could cost up to $1.3 million, with no guarantee of success and an ongoing risk of reinfestation.
That would require a rates increase, which councillors were not prepared to do.
Instead they left the door open for a future elimination attempt by asking staff to explore funding partnerships with external agencies.
Councillors were concerned about the potential environmental and economic impacts if the clam spread to other waterways, particularly Lakes Mangamahoe, Ratapiko and Rotorangi where they could affect hydroelectrical generation and irrigation systems.
They approved, in principle, an additional $250,000 for the biosecurity and Check, Clean, Dry programmes to identify and mitigate pathways, raise public awareness and reduce the risk of the gold clam spreading.
The money would also allow the council to increase its monitoring of Taranaki waterways for Corbicula and other freshwater pests.
Councillors made it clear Lake Rotomanu must remain closed to motorised boats, which pose the greatest risk of spreading the clam.
Council chair Craig Williamson said in an ideal world the council would love to eradicate the clams, especially as there was no evidence it spread to other Taranaki lakes. However the reality was the it could not afford to do it alone.
“There is a real opportunity for public and private partners to step up and work with us – we all have a lot to lose if the gold clam spreads unchecked in Taranaki. We’ll continue having those conversations and keep looking for practical solutions.
“In the meantime we must boost efforts to reduce the risk of spread, as well as increasing surveillance and preparedness. The onus is on boaties and other water users to take responsibility for their own backyards and Check, Clean, Dry every time they move between waterways, particularly if coming from the Waikato River.”
New Plymouth District Council, which owns Lake Rotomanu, had kept the lake closed to motorised boats and jet skis since the clams were discovered.
Conversations were now underway to determine if NPDC would extend that closure or if Biosecurity New Zealand would impose formal restrictions.
Recreational users such as kayakers, swimmers, remote-controlled boat enthusiasts and fishers could continue using the lake but were required to thoroughly check their gear.
The three treatment options identified in the report were killing the clams with copper ($600,000), draining the lake then applying salt ($900,000) and emptying the lake and pumping in seawater ($1.3 million).
They would all be complex operations, with only the copper option attempted before in New Zealand.
Gold clams were discovered in the New Plymouth lake in November 2025, the first confirmed infestation outside of Waikato.
Prolific breeders, they could clog water-based infrastructure, such as electricity generation plants, irrigation systems, and water treatment plants and competed with native species for food and space.
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– Published by EveningReport.nz and AsiaPacificReport.nz, see: MIL OSI in partnership with Radio New Zealand
