10/12/2025
𝗧𝗮𝗿𝗮𝗻𝗮𝗸𝗶 𝗹𝗮𝗸𝗲 𝘁𝗼 𝗯𝗲 𝗱𝗿𝗮𝗶𝗻𝗲𝗱 𝗶𝗻 𝗰𝗹𝗮𝗺 𝗳𝗶𝗴𝗵𝘁
An infestation of invasive clams has forced the draining of a popular lake in Ngāmotu for summer.
Lake Rotomanu will be emptied this week so scientists can understand the extent of the freshwater gold clam incursion.
The clam 𝘊𝘰𝘳𝘣𝘪𝘤𝘶𝘭𝘢 𝘧𝘭𝘶𝘮𝘪𝘯𝘦𝘢 was found in the recreational lake five weeks ago in the first discovery outside the Waikato River and the lake was closed to motorised boats.
New Plymouth District Council will open the lake outlet on Thursday and it’ll take four days to drain.
Fish will be harvested in partnership with local hapū and as many as possible used.
The lake would be empty for the summer, said Taranaki Regional Council (TRC) environment services manager Steve Ellis.
“It’s a popular summer spot and locals and visitors will be disappointed, but we hope they understand the reasons.”
“The invasive clam 𝘊𝘰𝘳𝘣𝘪𝘤𝘶𝘭𝘢 is a massive threat to our infrastructure, economy, ecosystems and recreational use of all the region’s waterways.
“We need to act now to give ourselves the best chance of preventing long-term damage or recreational restrictions.”
Ellis said test results and advice on river salinity and flow had been needed to make sure draining the lake wouldn’t spread the clams to the Waiwhakaiho River.
“We’re confident any clams or larvae will be quickly washed the short distance out to sea.”
The Department of Conservation website says young clams produce an invisible sticky thread of mucus which attaches to surfaces, like boats and recreational gear.
It says gold clams breed rapidly to form dense populations but it’s not known how the species will respond to New Zealand conditions
Gold clams could compete with native species for food and it’s unclear how they might impact whitebait.
The DOC site says gold clams had been difficult to control overseas and eradication had never been achieved.
TRC leads the new Regional Corbicula Coordination Group (RCCG) working with New Plymouth District Council, Ngāti Te Whiti hapū, Biosecurity NZ, Fish & Game, Earth Sciences NZ and others.
Ellis said elimination would likely be expensive and it’s unclear who would pay.
“There is no guarantee we will attempt to treat or eliminate the clams, even if it is technically feasible.
“We’re all aware of the massive economic damage these clams can do, so we’re having those conversations as a matter of urgency.”
An Earth Sciences team would survey the lakebed next week to find out how widespread the clams are, how deep they’ve burrowed and how old they are.
That would inform the next steps: whether elimination is feasible, what treatment options are and how much they’d cost.
Testing at Lakes Rotokare, Ratapiko, Rotorangi and the Waiwhakaiho River have not found any clams, and eDNA testing of the water has also been clear.
Ellis said that’s encouraging but doesn’t guarantee the clams aren’t present.
The councils are asking boaties, jet skiers, kayakers and other lake users to be extra vigilant over summer to avoid spreading the clam or other freshwater pests.
Official advice is to always follow the Check, Clean, Dry procedure when moving between waterways – and wake boats should ideally stick to one lake.
Biosecurity NZ would bring a washdown trailer to popular Taranaki lakes over the summer with staff and signs to spread the message and education via clubs, organisations and social media.
𝙇𝘿𝙍 𝙞𝙨 𝙡𝙤𝙘𝙖𝙡 𝙗𝙤𝙙𝙮 𝙟𝙤𝙪𝙧𝙣𝙖𝙡𝙞𝙨𝙢 𝙝𝙤𝙨𝙩𝙚𝙙 𝙗𝙮 𝙏𝙚 𝙆𝙤𝙧𝙞𝙢𝙖𝙠𝙤 𝙤 𝙏𝙖𝙧𝙖𝙣𝙖𝙠𝙞 𝙖𝙣𝙙 𝙛𝙪𝙣𝙙𝙚𝙙 𝙗𝙮 𝙏𝙚 𝙍𝙚𝙤 𝙄𝙧𝙞𝙧𝙖𝙣𝙜𝙞 𝙤 𝘼𝙤𝙩𝙚𝙖𝙧𝙤𝙖 𝙖𝙣𝙙 𝙄𝙧𝙞𝙧𝙖𝙣𝙜𝙞 𝙩𝙚 𝙈𝙤𝙩𝙪
