Fish & Game New Zealand is closely monitoring the situation at Lake Okataina near Rotorua amid iwi concerns about the spread of the invasive species gold clam.

"We’re working with mana whenua, Te Arawa Lakes Trust and the Ministry for Primary Industries to understand the risks of gold clams spreading from the Waikato River to the Rotorua lakes and looking at the science to better understand what this means for the health of freshwater and native and valued introduced species," says Fish & Game chief executive Corina Jordan.

"Gold clams have been confirmed in the Waikato River since May 2023 and, fortunately, have not been discovered elsewhere. This invasive species is mainly spread by boats with a ballast system, such as wake boats, and there is little risk of freshwater clams being spread by anglers.

"Fish & Game is deeply concerned about discussions to close Lake Okataina, particularly given the Waikato River system and Lake Karapiro are under next to no restrictions by MPI. We believe MPI and Waikato Regional Council should be taking stronger measures to prevent the spread of gold clams to other regions to address not only our concerns but also those of mana whenua.

"We’re disappointed MPI and the council have not invested more resources into isolating the gold clam at ‘ground-zero’ in the Waikato River.

"We believe other steps, such as a wash station at boat ramps, should have been installed as soon as the gold clams were discovered. We are now in a race against time to stop the spread.

"For more than a decade, Fish & Game has led the way in adopting good biosecurity practices at rivers and lakes across the country. This has included banning felt-soled waders and spearheading the implementation of the ‘check, clean, dry’ steps for angling gear, which is also recommended to prevent the spread of gold clams."

The Rotorua lakes attract 120,000-150,000 angler days per season. Lake Okataina is one of the renowned ‘trophy’ rainbow trout lakes within the Rotorua lakes fishery.

It provides a wilderness fishing location with high-quality trout fishing.

Fish & Game’s National Angler Survey highlights 6000- 7000 angler days recorded at the lake each season.

"We know anglers and other lake users are worried about the situation, especially on the eve of the opening of the angling season on October 1," says Jordan.

"As the country’s leading freshwater advocate, Fish & Game is committed to ensuring the wellbeing of all our lakes and streams. Lake Okataina is regarded as the food basket of the Rotorua region and is important to iwi, anglers and a range of other users.

"Fish & Game is urging anglers to continue following good biosecurity practices, including checking, cleaning and drying all gear and alert MPI if they see the clams. We will be keeping our licence holders updated about the situation."

The freshwater gold clam was discovered along a stretch of the Waikato River in May 2023. The clam is native to eastern Asia and is widely established in North and South America and Europe.

The clams reproduce rapidly and form large populations that can clog water-based infrastructure such as electricity generation plants, irrigation systems, and water treatment plants.

They are filter feeders that can potentially compete with native species for food.