Toxic algae could devastate riverside towns

Saturday, 7 February 2026

A boatie plows though a massive algal bloom on Lake Maraetai at Mangakino earlier this year. Locals say the poor state of the hydro lake on the Waikato River is turning people away.

Once touted as an anglers paradise, and a top water-sport playground on the Waikato River, Mangakino is in danger of becoming a ghost town as toxic algal blooms slowly suck the life out of its main attraction - Lake Maraetai.

Locals say cyanobacterial algal blooms in the river’s hydro lakes have become more frequent over the past five years, and when they arrive no-one can swim or fish in them.

Pets that come in contact with the blooms often die, and their human companions can suffer stomach complaints, respiratory issues, and skin irritations.

Mangakino home owner Karl Hitchcock says water quality in the Waikato River’s hydro lakes is getting worse and is a public health risk. He is applying for funding to have live web cameras installed at the lakes.

This summer, cyanobacterial health warnings are in place for all of the river’s hydro lakes.

The blooms appear as a green pea-soup-like scum on top of the water.

Mangakino business owners say the traditional summer surge has turned into a trickle over the past few years, but summer 2025/26 has been the worst.

No-one spoken to by the Waikato Times wanted to play the blame game - they just want authorities to work together to clean the lake, and restore their livelihoods.

Lake Ōhākurī, near the boat ramp, pictured here on Thursday, February 5 awash with algae.

Karl Hitchcock has been bringing his family to Mangakino for 18 years, and recently built a new home on the lake’s edge.

“Every year it gets worse … and I measure the water clarity of the lake all the time.

“Last year, when there was no rain for a long period of time, the lake was cleaner, and we were getting 4.7m visibility.

“At the moment it's about 1m, so when you're in the water, you can't see your feet.”

Mangakino’s YoYo Bakery owner Daniel Palangenu is throwing out food each day due to low demand. He said customers were asking why the lake was so bad this summer.

He said there was legislation in place that said the river’s water quality was supposed to get better, “not worse - that’s the law”.

“I know we can get it sorted out … but it’s trying to get regional council, district council, the Waikato River Authority, Mercury, and everyone else on board, which is a challenge.

“So we're just left with putting the information out there ourselves and raising awareness.”

Hitchcock said his main concern was around public health risks and a lack of real time monitoring, “so that people can have the latest information all the time”.

Recent algal blooms have turned parts of Lake Maraetai at Mangakino into a toxic pea-soup.

He said he dosen’t go swimming in the lake, but his family still wake board and ski on it.

“But we’re very careful not to drink any of it.”

He’s applying for funding to set up live web cameras at all of the hydro lakes, “so you can see if it’s gone green”.

Ata's Bar and Eatery in Mangakino is struggling to find customers this summer. Owner Ata Te Maari says the poor lake condition is turning people off. From left to right are locals Marlene Johnson, Ata Te Maari, Sheree Sutton, Sharyn Ahipene, and Danielle Kiss.

“Nobody fishes here anymore … they’re no good to eat anyway, and not in good condition.”

YoYo Bakery owner Daniel Palangenu said business had got progressively worse since the Covid pandemic, and this summer he was lucky to be making a few hundred dollars a day.

He said customers had complained about the poor state of the lake.

Lake Arapuni’s Arohena Campground had health warnings in place for toxic algae this summer. The camp was all but deserted when the Waikato Times recently visited the site.

“It’s like a ghost town this summer … out of town visitors are not staying for long, we all want the problem fixed.”

He said he was giving away, and throwing out food every day, due to a lack of customers.

Waikato Regional Council environmental science manager Mike Scarsbrook said a range of factors, including climate change, nutrient run off, hot settled weather, and river flow were exacerbating the problem at all of the river’s hydro lakes, “which during summertime and holiday periods is obviously really impactful on the community”.

Algal blooms in Lake Maraetai on the Waikato River are being driven by warmer water, low flow and nutrient discharges.

“The algae will build up faster with warmer temperatures.

“The long-term aim to reduce these blooms is to control the nutrients coming into the river … and the final thing is the flow through the system … which is controlled by Mercury (Energy).

“Closures associated with the blooms might last for longer than the community might think is reasonable, but it’s basically managing that health risk,” Scarsbrook said.

“The reality is that we'll likely see more blooms happen in future as the climate warms up and things continue to change.

Usually a bustling campground on the shores of Lake Maraetai at Mangakino, just a handful of visitors were on site on Waitangi Day week.

“It’s not what people want to do for their Christmas holiday - sit and look at a lake and not be allowed to go into it.”

He said controlling nutrients from entering hydro lakes was “very much intergenerational”.

“I'm really concerned about the signals the river is sending in terms of the things that are going on in it.

“There's quite a bit of research that we are doing to understand the river and hydro lakes better.

“Having a community with a high level of engagement and interest helps agencies such as ourselves because we're always having to prioritise where we put resources.

Lake Maraetai at Mangakino is also a site for the invasive gold clam pest species, and is plagued by toxic algal blooms over summer.

“Making their concerns known is actually a real positive because that helps us identify where we should be focusing our efforts.

“Local folk can actually be a part of the surveillance and monitoring of the system.”

Cafe worker Danielle Kiss said the usual summer visitor influx had just not happened this season.

“We've got to get this water quality up. If it wasn’t for that lake, we’d have nothing.

“If you don't have a healthy lake, you don't have people coming here.

“We had a couple of weeks that were busy, like over New Year's and stuff, but normally that lasts all through January, but no, not now.

“It’s definitely something that's on a lot of our minds.

“The river is meant to flow, and needs to be flushed out.

“I dived in there last year, rolled onto my back, floated for a bit, and after I got out I had bright red eyes for two days.”

Sheree Sutton said she usually worked every day over summer as a Bookabach cleaner.

“It used to be flat out from the beginning of December right through to after Waitangi weekend.

“It should be crazy, but they're not even getting busy … and if the lake's crap, what's the point of coming?”

Mangakino Central Charitable Trust general manager Marlene Johnson said the last time she swam in the lake was around four years ago.

“I won't even bother now … the water is disgusting.

“Everyone should be able to swim in our lake, we know it can be better but it’s just getting worse.”

Ata’s Bar and Eatery owner Ata Te Maari said visitor numbers had dropped so much she was in the process of selling both her home and business.

“It’s all about the lake … and it’s sad no-one is doing anything about it.

“It’s becoming the same story every year - once it turns green no-one can swim in it, and everyone leaves.”

Of the town’s approximately 600 residential properties, more than 55 are currently up for sale, but local Remax real estate salesperson Kath Shaw said that number has been consistent over the past few years.

She said the lake’s water quality was definitely a concern but had not seriously affected sales.

“The Mangakino and Whakamaru areas attract buyers who are seeking the relaxed, uncomplicated lifestyle there … with the golf course, and the cycle trails, and the water sports.

“So it's not always about the water sport community, and to be honest, from what I see, it hasn't really stopped them from using the lake.

“But it's certainly an issue that everyone's taking notice of and trying to do something about … but it’s not just Lake Maraetai, it's happening everywhere.”

She said house prices were “holding firm”, especially if a property was well maintained and offered views of the lake or river.

“Prices can range from $300,000 for a little bach that needs a lot of TLC to a $1.5 million dollar property.”