Now hear this - Sound waves could cure algae invasion

Saturday, 21 February 2026

Auckland-based company Hydro Synergy says it could clear Mangakino’s Lake Maraetai from toxic algal blooms in a matter of months.

It sounds almost too good to be true. An Auckland-based company says it could clear algae-infested Lake Maraetai in a matter of months by using high-frequency sound waves.

Hydro Synergy chief executive Ric Church said he’d been reading about toxic cyanobacterial blooms in the Waikato River’s hydro lakes after the Waikato Times highlighted the problems it has been causing in Mangakino’s Lake Maraetai.

Locals say visitors were leaving Mangakino in droves this summer, businesses were suffering, residents were selling up, and calls for action to remove the toxic algae were falling on deaf ears.

Hydro Synergy chief executive Ric Church said he’s confident two of his units could kill all the toxic algae in Lake Maraetai within 60 days.

All of the river’s eight hydro lakes have had toxic algae warnings placed on them this summer, with no one coming forward with a possible solution, until now.

Church said two of Hydro Synergy’s $70,000 to $80,000 units placed into the slow moving waters of Lake Maraetai would do the trick, and was so confident he guaranteed they would remove 90% of its algae within 60 days.

“The economic and public health consequences of poor water quality in these areas are evident, and as residents noted, the situation is becoming critical,” he said.

Before and after photos of Lake Tewa, a man-made lake in the South Island where Hydro Synergy was tasked with the removal of toxic algae last year.

Church said Hydro Synergy makes devices that sit in lakes, ponds, reservoirs, or industrial water systems, and use very high-frequency sound waves (ultrasound) to control algae and other unwanted growth.

Instead of using chemicals, the sound waves interfere with the algae at a microscopic level so they can’t grow properly.

The units are solar-powered, and easy to maintain, and have been tested in private lakes and commercial operations in the South Island with flying colours.

Waikato River Authority chief executive Antoine Coffin says the overall health of the river was declining, and was open to discussing how new technology could be put to use.

“To date, most remediations have relied on chemical solutions, but we’ve been testing and proving a more sustainable path,” Church said.

“In recent projects we’ve achieved a 99 to 100% reduction in cyanobacteria within just a few weeks.”

“We currently have a major trial underway at Lake Hood … being monitored by Lincoln University, Cawthron Institute, Earth Sciences NZ, and the Ashburton District Council.

Hydro Synergy units helped remove, and prevent the return, of algae on nets used by Mount Cook Alpine Salmon.

“Many other councils are holding their breath for the final data before they commit.

“But in our experience, fiscal constraints often dictate water quality decisions until it becomes an emergency.”

He said their technology has the potential to remove toxic algae from slow moving water ways all over the country, and the world.

A toxic algal bloom in Lake Ōhākurī pictured earlier this month.

“We started working with Mount Cook Alpine Salmon, they had an issue with cyanobacteria coming into their farms … and with algae that was forming on their nets.

“They needed a solution because they were cleaning weekly or biweekly throughout the year, and when we put our equipment into the water for a trial, which lasted for nine months, they didn't need to clean their nets at all.”

Lake Tewa is a small man-made lake inland from Lake Whakatipu where Church said the water was so infected with cyanobacteria that “it actually looked like a paint-like scum”.

A Hydro Synergy unit in use at a man-made lake in the South Island.

“Now we have zero cyanobacteria in that lake, and we would now class it as a trophy lake.”

A report states Lake Tewa has moved from “severe biological instability to stable ecological recovery” after the system was introduced.

“Monitoring confirms a 100% reduction in toxic cyanobacterial populations,” the report states.

“Right now, we’re called in as the ambulance at the bottom of the cliff. We go and remediate the water because there’s historical cyanobacteria in there,” Church said.

“There’s a large amount of funding being put to monitoring … which haven’t been put to solutions because there haven’t been any solutions other than chemical solutions, and we don’t want to do that to our water bodies.

“We would be happy to work with the community to get equipment out there to protect them.

“I come from Whanganui, and the Whanganui River is deemed to have its own rights, what's stopping the Waikato River going and getting the same rights?

“Once lakes die, it’s very hard to return that lake back to health so we need to be catching these lakes before they completely die.”

Waikato River Authority chief executive Antoine Coffin said the authority was not happy with the state of the river, and would take a look at Hydro Synergy’s technology.

Coffin said the situation highlighted by the Waikato Times at Mangakino’s Lake Maraetai was “not very good at all”.

“It's part of the New Zealand tradition that you go out into the natural environment, lakes and rivers and beaches, and there may have been a family tradition in going to those places.

“You'll hear people in those communities remember what it was like, and you'd hope that those environments are there for future generations to enjoy like previous generations have enjoyed them, so I completely understand people are very concerned, and we're concerned as well.”

The authority was set up in 2010, and its vision “is for a future where a healthy Waikato River sustains abundant life and prosperous communities who, in turn, are all responsible for restoring and protecting the health and wellbeing of the Waikato River, and all it embraces, for generations to come”.

He said the river’s health had been degrading “for quite some time, since at least the 1980s”.

“That's obviously caused by human activity.

“We're tasked with the long-term restoration of the health and well-being of the river, and we need other agencies and communities to work with us to achieve that.

“We have good participation … and we’re doing good work on their land so it's not all bad news.

“There are some places where the water quality has really improved.

“But you look at the whole of the river, and overall it’s still declining.

“Technologies that farmers are using like Halter are potentially a game changer, you're able to know where your stock are at any moment of the day,” Coffin said.

“Some of the stuff they're doing is fantastic.”

Coffin said “the status quo is quite powerful” and that changing the way people have always done things, “especially where it's beneficial to them, is quite hard to do”.

He said the authority would look into Hydro Synergy’s technology.

“I have to be convinced that it's going be different, and be better, but that takes a bit of time.

“It is a very significant claim.

“We just need to be professional about it … if there's something that could be fit for purpose then we’re absolutely open to having a look at it.”