Freshwater gold clam invasion: Northland’s Kai Iwi Lakes boaties will undergo compulsory checks

Freshwater gold clam biosecurity checking at Lake Taharoa's Marina Bay boat ramp last week. Photo / NRC

Visitors taking their boats and gear to Northland’s busiest tourist lake will have to go through compulsory biosecurity checks from Friday.

The new measure comes as concerns grow over the threat of pest freshwater gold clam invasion.

Staff from councils and tangata whenua kaitiaki will be carrying out biosecurity checks of boats and gear at Kaipara’s Kai Iwi Lakes over the summer tourist peak, between December 22 and February 6.

The invasive gold clam was discovered in the Waikato River in May, but has so far not been found in Northland’s lakes.

Under the Kaipara District Council‘s (KDC) Taharoa Domain Bylaw 2018, the owner or master of a vessel can be denied access to the lakes if they refuse a biosecurity check.

As many as 2000 people descend on Lake Taharoa and surrounds each day as 75,000 people visit Kai Iwi Lakes over the summer season.

Lake Taharoa is popular with thousands of visitors who flock there from around the country. Photo / Susan Botting

Thousands of power boats, jet skis, kayaks and yachts use Lake Taharoa, which is under increasing pressure from overuse.

However, there are no easy-to-see freshwater gold clam warning signs around the lake’s Marina Bay boat ramp or the KDC’s main Pine Beach campground.

Messages around clam-specific “check, clean, dry” processes for boats will also be pushed during biosecurity checking.

The Kai Iwi Lakes are home to at-risk dune lakes galaxias (small native fish) and critically endangered lake plants which are at high risk of extinction.

Strict new government controls aim to stop the pest’s spread from the 225km of freshwater gold clam-infested Waikato River.

No wake boat that has been on this stretch is allowed to be used on any other lake, river or estuary in New Zealand.

Biosecurity New Zealand deputy director-general Stuart Anderson said it was illegal to knowingly transport the freshwater gold clam.

The Waikato River is four hours’ drive from Kai Iwi Lakes.

The Northland Regional Council (NRC), with biosecurity responsibilities, and the KDC are working with Te Roroa iwi and Te Kuihi hapū to keep freshwater gold clams out of the lakes.

KDC general manager customer experience Hayley Worthington said Kai Iwi Lakes’ visitors must follow the new, clam-specific “check, clean, dry” procedures for their boats and gear. They needed to do so before leaving home.

Normal “check, clean, dry” methods do not work for the gold clam, which can survive for up to 10 days out of water.

Kayaks and boats - especially wake boats with their internal ballast tanks - are the highest clam-spreading risks.

Freshwater gold clams from the 225km of Waikato River now infested with the pest. Photo / MPI

Taharoa domain governance committee member and Te Roroa general manager Snow Tane said the Kai Iwi Lakes were a taonga for Aotearoa because of the species they were home to.

Te Kuihi spokesman and governance committee member Ric Pārore said preventing the spread of invasive species like gold clams upheld the mauri (life force) of the lakes and ensured they remained unspoiled for future generations.

Kaipara Mayor Craig Jepson said education was needed to prevent the clam reaching Kai Iwi Lakes.

“The invasive freshwater clam could have significant ecological and economic impacts if it becomes established in the lakes.”

Each clam can produce 400 offspring a day, without a partner. Their shell debris builds metres-deep on lake floors.

NRC and KDC’s co-governed domain governance committee pushed to close Lake Taharoa’s Marina Bay boat ramp over summer to slash the risk of freshwater gold clam arrival. But KDC councillors on November 29 voted five to four against doing so.

NRC’s Crawford said it was hard, if not impossible, to fully empty and dry boat ballast tanks, which meant the clam could survive between boating sites.

“Best practice is to use a high-pressure steam cleaner or a power wash on to grass or gravel where there is no likelihood of runoff entering back into a waterway or stormwater system.”

“For absorbent materials, such as lifejackets or waders, they must be frozen overnight, or washed with a 10 percent bleach solution, or washed in hot water (45C degrees plus) for 20 minutes.”

Further information about gold clams is available from biosecurity.govt.nz.

■ Local Democracy Reporting is Public Interest Journalism funded through NZ On Air