Invasive gold clams found in Lake Rotomanu by eagle-eyed youngster

Wednesday, 12 November 2025

The invasive gold clam pest has been discovered at New Plymouth’s Lake Rotomanu by an eagle-eyed youngster fishing for trout.

The lake was now closed to motorised watercraft, following the discovery of the freshwater clam Corbicula fluminea, also called the gold clam.

Each clam could spawn 70,000 clams, which was why they were so invasive, Taranaki Regional Council biosecurity programme lead Lisa Hardegger said.

The tiny clams can blanket river and lake beds, compete with native species for food, clog critical water infrastructure and degrade water quality.

Overseas, it had been difficult to control, and eradication had never been achieved.

The gold clam was first discovered in the Waikato River in 2023. It was not known how it came into New Zealand.

It was disappointing to find it in Taranaki, Hardegger said.

“We are the first incursion outside of the Waikato zone.”

The clam was found during the Taranaki Fish & Game 'Take a Kid Fishing' event last Saturday. A biosecurity staff member had a stand at the event showing pictures of the clams.

A young boy came up and said he’d seen one. He was asked if he had seen it in Waikato, she said.

“And he went, ‘no, just over here’.”

They're the size of half a fingernail, Hardegger said.

“So, a really eagle-eyed little man, who was just incredible.”

Two Taranaki biosecurity staff and two from the Ministry of Primary Industries in Wellington, were at Lake Rotomanu on Wednesday donning waders to go into the lake to see how far the clams had spread.

“We’re still investigating and doing surveillance,” Hardegger said.

It was a “big call” to close the lake to boats, “but the right call to make sure it hasn’t spread to every other lake around the region if it’s not already there”.

There had been a programme running for 15 years raising awareness around cleaning boats and other water craft, she said.

“It's about basically if you have a kayak, if you have a boat, a wakeboard, a surf ski, anything else in the water, you should, when you take it out of the water, you check it, you clean it, you dry it. That's our basic message.”

Taranaki Regional Council Environment Services Manager Steve Ellis said how the clams got into the lake was still unknown, but they had possibly been spread by someone who had been in the Waikato River and did not clean their boat or water gear properly.

As an interim measure, New Plymouth District Council had closed the lake to motorised boats, which were at the highest risk of spreading clams. Other recreational users will be required to thoroughly check, clean and dry all gear before leaving the lake shore, Ellis said.

“We appreciate it is coming into summer, and the lake is a favourite spot for many boaties. But they will understand how important it is we act quickly – Corbicula can take over a waterway and have long-term effects on not just recreation, but also the environment.”

Surveys were being carried out this week to see if the clams were in the Waiwhakaiho River as well as other lakes across Taranaki.

Once those results were available, decisions would be made around managing the incursion and what, if any, restrictions would remain in place, Ellis said.

“We are asking for the public’s support. Whether it’s Lake Rotomanu or any other waterway, it's more important than ever you check, clean and dry everything that has been in contact with the water before moving between waterways.”

Additional signage would be erected by the weekend, with staff on site to ensure the rules were followed and to advise people how to correctly clean their gear. Road access and car parks would remain open.